EFFECTS OF TEMPERATURE ON THE EFFECTIVENESS OF THE …

EFFECTS OF TEMPERATURE ON THE EFFECTIVENESS OF THE TRIPLE LAYER

HERMETIC BAG AGAINST THE LARGER GRAIN BORER Prostephanus truncatus

(COLEOPTERA: BOSTRICHIDAE) AND MAIZE WEEVIL Sitophilus zeamais

(COLEOPTERA: CURCULIONIDAE) IN STORED MAIZE

BY

JINATU, LAMI WAMDEO

B.AGRIC (HONS) CROP PROTECTION UNIVERSITY OF MAIDUGURI, BORNO

STATE, NIGERIA

THIS THESIS IS SUBMITTED TO THE UNIVERSITY OF GHANA, LEGON IN

PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE AWARD OF

MASTERS OF PHILOSOPHY DEGREE IN ENTOMOLOGY

INSECT SCIENCE PROGRAMME

UNIVERSITY OF GHANA, LEGON

JULY 2015

JOINT INTERFACULTY PROGRAMME FOR THE TRAINING OF ENTOMOLOGIST

IN WEST AFRICA. COLLABORATING DEPARTMENTS: ANIMAL BIOLOGY AND

CONSERVATION SCIENCE (SCHOOL OF BIOLOGICAL SCIENCES) AND CROP

SCIENCE (SCHOOL OF AGRICULTURE) ALL OF THE COLLEGE OF BASIC AND

APPLIED SCIENCES

University of Ghana http://ugspace.ug.edu.gh

1

DEDICATION

To God Almighty and my parents, Rev. & Mrs. Jinatu L. Wamdeo


2

ACKNOWLEDGEMENTS

I am thankful to God Almighty for the gift of life sustenance throughout the course of my study.

I am greatly indebted to DAAD for sponsoring me through the twenty four (24) months period of

the course. My sincere gratitude goes to my supervisors Prof. Kwame Afreh-Nuamah and Dr.

Fatunbi Oluwole Abiodun. They made time out of their busy schedule to patiently guide, listen

and correct my numerous mistakes. Their patience impacted greatly on this work and made it a

reality.

I appreciate the coordinator of ARPPIS, Dr. Rosina Kyeremanten and all the ARPPIS’ lecturers

and staff for shaping my future as an entomologist. May the Lord bless and reward you for all

the time you have taken to be in the classroom to teach us not only entomology but moral

lessons.

My profound gratitude goes to Bio-Plastics Limited, Accra Ghana for providing me with the

triple layer hermetic bag at no cost. Lots of thanks go to my colleagues for being there

academically and socially. You guys have been my family in diaspora. May God keep the bond

between us even after ARPPIS. To Hettie Boafo, Joseph Chabi, Aikins and the VESTERGADD

laboratory, I appreciate your kindness and friendship for letting me use your equipment and

teaching me a lot of things.

Tonnes of gratitude go to my parents, siblings and friends for their constant prayers and goodwill

messages. God bless you all.


3

TABLE OF CONTENTS

DECLARATION……………………………………………………………………………….. i

DEDICATION………………………………………………………………………………….. ii

ACKNOWLEDGEMENT……………………………………………………………………… iii

TABLE OF CONTENT ………………………………………………………………………… iv

LIST OF FIGURES ……………………………………………………………………………. vii

LIST OF TABLES ……………………………………………………………………………… ix

LIST OF PLATES ……………………………………………………………………………..... x

ABSTRACT …………………………………………………………………………………… xi

CHAPTER ONE ………………………………………………………………………………... 1

1.0 INTRODUCTION…………………………………………………………………………… 1

1.1 Background ………………………………………………………………………………...... 1

1. 2 Justification………………………………………………………………………………...... 3

1.3 Objectives ………………………………………………………………………………….... 5

CHAPTER TWO ………………………………………………………………………………... 6

2.0 LITERATURE REVIEW …………………………………………………………………… 6

2.1 Origin and Distribution of Maize …………………………………………………………… 6

2.1.1 Uses of Maize ……………………………………………………………………………... 7

2.2 Stored Products ……………………………………………………………………………… 7

2.2.1 Temperature ……………………………………………………………………………...... 7

2.2.2 Moisture Content ………………………………………………………………………….. 8

2.2.3 Relative Humidity ………………………………………………………………………... 8

2.2.4 Interactions between Temperature and Relative Humidity …………………………….... 9

2.3 Prostephanus truncatus ………………………………………………………………......... 10

2.3.1 Taxonomic Tree ………………………………………………………………………….. 11

2.4 Sitophilus zeamais ………………………………………………………………………… 13

2.4.1 Taxonomic tree ………………………………………………………………………….. 13


4

2.5 Post harvest Technology …………………………………………………………………… 15

2.5.1 Methods of storage ………………………………………………………………………. 17

2.5.1.1 Cribs …………………………………………………………………………………… 17

2.5.1.2 Banco/Mamrusi/Kusasi/Rumbu Granaries ……………………………………………. 18

2.5.1.3 Metal Silos …………………………………………………………………………….. 20

2.5.1.4 Warehouses ……………………………………………………………………………. 20

2.6 Hermetic storage …………………………………………………………………………… 21

2.6.1 Postcosecha galvanized steel silos ……………………………………………………….. 21

2.6.2 Polyethene bags …………………………………………………………………………. 22

2.6.2 Purdue Improved Cowpea Storage (PICS) System …………………………………....... 23

2.6.3 GrainPro ultra-hermetic bags ……………………………………………………………. 24

2.7 Practical Hermetic Storage ………………………………………………………………… 24

CHAPTER THREE ……………………………………………………………………………. 27

3.0 MATERIAL AND METHODS …………………………………………………………… 27

3.1 Study Site ……………………………………………………………………………….….. 27

3.2 Sources of Experimental Materials ………………………………………………………… 27

3.2.1 The maize ………………………………………………………………………………… 27

3.2.2 The Triple Layer Hermetic Bags ………………………………………………………… 27

3.2.3 Culturing the Insects …………………………………………………………………….. 27

3.2.4 Temperature Regulators …………………………………………………………………. 28

3.3 Laboratory experiments …………………………………………………………………… 28

3.3.1 Experimental design ……………………………………………………………………... 28

3.4 Effect of Temperature on the Efficacy of the Triple Layer Hermetic Bag ………............... 30

3.4.1 Procedure for Determining Weight Loss ………………………………………………… 30

3.5 Determining Rate of Oxygen Depletion ………………………………………………...…. 31

3.6 Determination of Changes in the Tensile Strength of the Hermetic Bags …………………. 32

3.7 Determination number of live insects found ……………………………………………….. 33


5

3.8 Determination of Seed Viability ………………………………………………………….... 34

3.9 Data Analysis …………………………………………………………………………….… 34

CHAPTER FOUR ………………………………………………………………………….….. 35

4.0 RESULTS ……………………………………………………………………………….…. 35

4.1 Moisture Content ………………………………………………………………………..…. 35

4.2 Effect of temperature on the tensile strength of the polyethene bag …………………….... 38

4.3 Result and analysis of Weight loss …………………………………………………..…….. 43

4.4 Number of live insects ………………………………………………………….………….. 49

4.5 Oxygen depletion level ……………………………………………………………….……. 53

4.6 Percentage germination viability ………………………………………………………...… 54

CHAPTER FIVE …………………………………………………………………………..…... 56

5.0 Discussions ………………………………………………………………………………… 56

5.1 Moisture Content …………………………………………………………………………... 56

5.2 Number of Live Insects ……………………………………………………………………. 57

5.3 Weight Loss …………………………………………………………………………........... 59

5.4 Germination Potential ……………………………………………………………...………. 60

5.5 Oxygen Depletion ………………………………………………………………….………. 61

5.6 Tensile Strength …………………………………………………………………..………... 62

Chapter Six …………………………………...………………………………………………… 63

6.0 Conclusion and Recommendation …………………………………………………………. 63

6.1 Conclusion ………………………………………………………………………….……… 63

6.2 Recommendation …………………………………………………………………………... 65

REFRENCES ………………………………………………………………………………....... 66

APPENDICES …………………………………………………………………………………. 82


6

LIST OF FIGURES

Figure 1 Distribution of S. zeamais in Africa ……………………………………………...……16

Figure 2 Distribution of P. truncatus in Africa ………………………………………………….16

Figure 3: Moisture content of maize in triple layer hermetic and polypropylene bags in three (3)

different temperature conditions. ………………………………………………………………. 41

Figure 4 Tensile strength of polythene at the start of storage ………………………………….. 42

Figure 5: Tensile strength of polythene after 60, 120 and 180 days under storage temperature

38˚C ...............................................................................................................………………….. 43

Figure 6: Tensile strength of polythene after 60, 120 and 180 days 18oC under storage

temperature …………………………………………………………………………………….. 44

Figure 7 Tensile strength of polythene after 60, 120 and 180 days under room temperature … 45

Figure 8 Mean weight loss of maize for six months of storage ………………………………. 48

Figure 9 Percentage weight losses by insect species and storage bag under 38˚C storage

condition over 6 months ……………………………………………………………………… 49

Figure 10 Percentage weight losses by insect species and storage bag under 18˚C storage

condition over 6 months ………………………………………………………………………. 50

Figure 11 Percentage weight losses by insect species and storage bag under room temperature

(27˚C-32˚C) storage condition over 6 months ………………………………………………… 51


7

Figure 12 Mean Percentage Weight Loss of maize stored under different temperature conditions

in triple layer hermetic and polypropylene storage bags over period of six (6) months ……… 52

Figure 13 Mean number of live insects in different storage bags under different temperature

conditions after six (6) months of storage……………………………………………………... 54

Figure 14 Oxygen depletion rate in hermetic bags under the three storage condition ……… 57

Figure 15 Germination potential of maize stored under different conditions in two storage bags

………………………………………………………………………………………………… 59


8

LIST OF TABLES

Table 1 Acronyms for the different treatment combinations …………………………………... 32

Table 2 Mean moisture content for six (6) months in different treatment combinations ……… 40

Table 3 Yield point of tensile strength of polythene material as represented on the graph ……. 46

Table 4 Means and standard errors of differences for weight losses and number of live insects 55

Table 5 Linear correlation and regression analysis between the storage time (X) and weight loss

or number of live insects (Y) as influenced by various treatment combinations ………………. 56


9

LIST OF PLATES

Plate 1: A Bamboo Crib ……………………………………………………………………….. 20

Plate 2: Traditional maize storage systems ……………………………………………………. 21

Plate 3. SCY-2A Oxygen Analyser …………………………………………………………… 35

Plate 4: Hounsfield Texture Analyser …………………………………………………………. 36


10

LIST OF APPENDICES

Appendix 1 Maize stored hermetically after six months under 38˚C …………………….. 82

Appendix 2 Maize stored hermetically after six months under room temperature ………. 82

Appendix 3 Maize stored hermetically after 6 months under 18˚C ……………………….. 83

Appendix 4 Student sieving maize for counting live insects at entomology laboratory …… 83

Appendix 5 Pieces of hermetic polythene materials cut to be tested ………………………. 84

Appendix 7 ANOVA table from GenStat ……………………………………………………… 84


11

ABSTRACT

The study examined the effect of temperature on the effectiveness of the triple layer hermetic

bag in controlling P. truncatus and S. zeamais damaging maize in the store and how the

temperature affects the tensile strength of the polyethene material used. The specific objectives

include determination of the moisture content, oxygen depletion rate and seed viability of the

maize. Five (5) kilogrammes of local maize variety (Abrodenkye) with initial moisture content of

14.6% was used for the experiment to fill each experimental storage bag. Two insect species, S.

zeamais and P. truncatus were introduced in the bag. Three (3) temperature conditions (38oC,

18oC and room temperature (27o-32oC)) were used to store the maize in triple layer hermetic

storage bag with polypropylene bag as control. Destructive samplings without replacement were

conducted every month for the period of six (6) months. Thousand grain mass (TGM) method of

weight loss assessment was used to determine the weight loss of the grain monthly. Results

showed significant difference (p<0.001) in weight loss among the different temperatures. Weight

loss was least in the triple layer hermetic bag at 18oC (0.41% and 1.21% for S. zeamais and P.

truncatus respectively while 38oC and room temperature (27o-32oC) recorded the highest weight

loss 20.12% and 28.15% respectively. P. truncatus caused the highest weight loss of 28.15% and

was more destructive based on the powder produced due to feeding while S. zeamais caused

20.12% weight loss at the end of six (6) months. Numbers of live insects were significantly

different between storage bags in different temperatures and among temperatures for both insect

species. Results of the tensile strength showed that high temperature increased the ductility of

the polyethene material with time. The tensile strength increased to 42.2 from its initial 33.4 at

the end of six months of storage. Relatively, low temperature maintained the tensile strength

throughout the experiment. On the other hand, fluctuations of temperature at the room


12

temperature decreased the tensile strength making it brittle, fragmented and unsafe for long term

usage in such geo-climatic zones. Moisture content and seed viability were significantly different

(P<0.001) among various temperatures and between storage bags. The hermetic bag infested

with S. zeamais at 18oC recorded highest seed viability and P. truncatus infested maize in

polypropylene bag at room temperature (27o-32oC) recording the least seed viability. The study

further revealed that although high density polyethene depletes oxygen completely and is 100%

efficient in controlling insects, it cannot be used for long term storage in high temperature zones

because it increases the moisture content of the maize and promotes the build-up of mould. It is

recommended that farmers should be made aware of the choice of hermetic bag to be used

according to their climatic zones.


13

CHAPTER ONE

1.0 INTRODUCTION

1.1 Background

Maize (Zea mais L.) is the third most important cereal grain worldwide after wheat and rice

(Golob et al., 2004). It is referred to as the cereal of the future for its nutritional value and

utilization of its products and by-products (Lee, 1999). Worldwide production of maize is 820

million tons, with the United States, the largest producer, producing about 332 million tons and

Africa producing 59.9 million tons (FAOStat, 2009). The demand for maize was estimated to

increase by 50%, from 558 million metric tons in 1995 to over 800 million metric tons in 2020

(Martinez et al., 2011). This enormous increase has been attributed to diverse uses of corn, from

food and animal feed to ethanol production (FAO, 2006). It is a basic staple food grain for large

parts of the world including Africa, Latin America, and Asia (Yaouba et al., 2012).

Maize (Zea mais L.) has become an important staple food crop in all parts of Ghana. Currently,

maize has replaced sorghum and millet as the traditional food security crop in the drier northern

savannah areas. It is the most cultivated cereal in Ghana, occupying up to 1,023,000 ha on arable

land compared to rice (197,000 ha), millet (179,000 ha), sorghum (243,000 ha), cassava (889,013

ha), yam (204,000 ha) and plantain (336,000) (SRID, Ghana, 2013). However, the country is a

net-importer of maize even though it has great potential to be self-sufficient and net exporter. Per

capita consumption of maize is estimated at 44 kg/person/year (FAO, 2013). After harvest, maize

is stored on cobs in traditional grain silos or shelled into jute or polypropylene sacs with or

without protection from storage pests and/or environmental hazards. However, stored maize can

be damaged by insect pests if they are not properly conditioned and protected. Stored-product


14

arthropods can cause serious postharvest losses, estimated at 5-15% in developed countries and

20-50% or more in developing countries (De Lima, 1981).

It is estimated that each year, between 25 and 40% of stored agricultural produce is lost in the

tropics because of inadequate farm- and village-level storage (Hayma, 2003). In the field and

during storage the products are threatened by insects, rodents, birds and other pests. Moreover,

the product may be spoiled by infection from fungi or bacteria. When dried to moisture content

below the safe moisture level, cereals and pulses can be stored for period of a year or more under

a wide range of temperatures, provided that during storage the moisture level does not rise, and

precautions against insects are taken; insects may still develop at a relative humidity of

approximately 35% and temperatures of around 15°C. Conservative estimates are that close to

one-third of the world’s food crops is damaged by insects during growth and storage. World-

wide, more than 200 species of insects are recorded as damaging to maize both on the field and

in store. Storage pests of maize include the larger grain borer (Prostephanus truncatus), the

maize weevil (Sitophilus zeamais), the flour beetles (Tribolium casteneum and T. confusum),

lesser grain borer (Rhyzopertha dominica), maize weevil, granary weevil (S. granarius) and

(Sitotroga cerealella) (Obeng-Ofori & Boateng, 2008).

Under many circumstances, the most rapid and economic method of controlling insects is the use

of synthetic insecticides such as Actellic (Pirimiphos methyl), bioresmethrin (pyrethroid),

phostoxin (Aluminum phosphate) (Obeng-Ofori, 2008). It has been established that plant

powders and oils such as neem (Azadirachta indica), black pepper (Piper nigrum), chili pepper

(Capsicum annuum), cinnamon (Cinnamomum aromaticum), turmeric (Curcuma longa),

Zanthoxylum xanthoxyloides and Securidaca longependuncata has repellency or toxicity effect

against stored-product insects (Abudulai, et al., (2002); Shayesteh & Ashouri (2010); Eziah, et


15

al., (2013)). A relatively new development is the hermetically sealed bag or cocoon of various

sizes (1 – 300 metric ton), which appear to offer good possibilities to store grain in a variety of

quantities. The hermetic bags work on the principal that grains release carbon dioxide which

rapidly replaces the oxygen in the sealed container. Once oxygen is exhausted, the pests die and

fungi cannot spread. For these sealed units to work effectively, they need to be completely filled

quickly and only open when the entire contents have to be used. ( Forbes, 2007)

1.2 Justification

Efforts to improve maize production through plant breeding and improved management options

have made remarkable progress in increasing yields during the past century (Cairns et al., 2012).

However, with limited attention on storage of the grains, Ghana like other developing countries,

experiences serious problems with availability of quality maize, which often arise from poor

storage (Armah and Asante, 2006). This situation is most common among small holder farmers

who produce the bulk of maize in Africa. Over the past half century, the most rapid and

economic method of controlling insects was the use of synthetic chemical pesticide for field and

post-harvest protection of crops (Kamel, 2010). However, most of the contact insecticides used

in stored product insect pest management are lipophilic and accumulate in areas of high fat

content especially the germ and bran of cereals (Mensah et al., 1979, Eziah, et al., 2013). These

toxic residues tend to persist in the treated products which may have a harmful effect on the

consumer, affect non-target organisms which could be beneficial in nature as well as lead to

insecticide resistance by the target insects. Indiscriminate use of common grain protectants such

as Actellic (Pirimiphos methyl), bioresmethrin (pyrethroid), and phostoxin (Aluminum

phosphate) is common among small-holder farmers (Ogbonna, 2013). Most farmers acquire

agro-chemicals from unaccredited input dealers without proper knowledge or training on


16

appropriate usage of the chemicals. Also, phosphine fumigation is widely undertaken in unsealed

silos and poor sanitation conditions resulting in control failures with phosphine. In as much as

the repellency or toxicity of neem (Azadirachta indica), black pepper (Piper nigrum), chili

pepper (Capsicum annuum), cinnamon (Cinnamomum aromaticum), turmeric (Curcuma longa),

Zanthoxylum xanthoxyloides and Securidaca longependuncata among others against stored-

product insects have been well established (Abdullai et al., (2002); Shayesteh & Ashouri (2010);

Eziah et al., (2013)) and although these products have obviously little environmental hazards and

low mammalian toxicity, few farmers tend to resort to the option of using them because they lack

rapid knockdown effect, particularly where infestation already exist. More so, these botanicals

have several limitations which include, technical problems related to collection, processing and

storage (Obeng-Ofori, 2008), in addition to the need of toxicological and safety data for

registration and use (Navarro, 2006). Therefore, a need arises for storage technologies that are

environmentally sustainable and suitable for small holder farmers’ use in order to maintain

quality of grains in store hence, the hermetic storage. The hermetic storage, now becoming

widespread, uses modern low permeability plastic materials which are light-weight and can be

used outdoors and indoors, have long lifespan and can be transported when full (Anankware et

al., 2013). Hermetic storage in plastics, have proven to be successful in recent years (Villers et

al., 2008; Jonfia-Essien et al., 2010; Anon, 2011; Navarro et al., 2012). But pollution from

plastics poses threats to marine biodiversity already at risk from overfishing, climate change and

other forms of anthropogenic disturbance (Derraik, 2002). For that reason, the Forum for

Agricultural Research in Africa (FARA) came up with the use of biodegradable hermetic

storage bags in 2012 an this was tested for widespread use within the research programme of the

African Postgraduate Programme in Insect Science (ARPPIS). It was observed that the


17

biodegradable polyethylene liners began to fragment after 6 months of storage when

temperatures were extreme 30-40 oC in store (Ansah et al., 2015). This could be due to oxidative

degradation of the d2w pro-oxidant additive of the biodegradable bag, as its exposure to the sun’s

radiation results in degradation as reported by Arnaud et al., (1994); Satoto et al., (1997);

Koutny et al., (2006); and Ojeda et al., (2009)).

The research focused on assessing the effectiveness of biodegradable plastic bags in hermetic

storage for the storage maize under different temperature conditions to simulate the maximum,

minimum and mean temperatures in parts of sub-Saharan Africa. This will further elucidate how

temperature affects the hermetic bags under extended period of use.

1.3 Objectives

The main objective of this work was to determine the effect of temperature on the effectiveness

of the triple layer hermetic bag against the larger grain borer (LGB), Prostephanus truncatus,

and Sitophilus zeamais in stored maize.

The specific objectives include Determining:

1. Oxygen level in the hermetic bags at different temperature regimes over time in storage.

2. Changes in the tensile strength of the hermetic storage bag under different temperatures

over time in storage.

3. Percentage mortality of the insect pests in the hermetic bag over time at different

temperature regimes

4. Seed viability of the grain after storage under different temperature conditions


18

CHAPTER TWO

LITERATURE REVIEW

2.1 Origin and Distribution of Maize

The primary centre of origin of maize is considered by most authorities to be Central America

and Mexico. The discovery of fossil maize pollen with other archaeological evidence in Mexico

indicates Mexico to be the native of maize. At first, maize was only a garden curiosity in Europe,

but it soon began to be recognized as a valuable food crop. Within a few years, it spread

throughout France, Italy, and all of south-eastern Europe and northern Africa. By 1575, it was

making its way into western China, and had become important in the Philippines and the East

Indies. (Gibson and Benson, 2002).

Maize is cultivated throughout the world from 58°N latitude to 40°S latitude. The United States

produces 40% of the world's harvest; other top producing countries include China, Brazil,

Mexico, Indonesia, India, France and Argentina. Worldwide production was 872,006,770 Mt

tonnes, in 2012, more than rice (719,738,273 Mt) or wheat (670,875,110 Mt) (FAOStat, 2015).

In 2009, over 159 million hectares (390 million acres) of maize were planted worldwide, with a

yield of over 5 tonnes per hectare (80 bu/acre). Production can be significantly higher in certain

regions of the world; 2009 forecasts for production in Iowa were 11614 kg/ha (185 bu/acre).

(Cedar Rapids Gazette, 2009). There is conflicting evidence to support the hypothesis that maize

yield potential has increased over the past few decades ( Duvick, & Cassman, 2009).


19

2.1.1 Uses of Maize

After harvest the crop is usually dried and stored for sale, food or to be used as seeds. In some

African countries like Nigeria and Ghana, maize is processed in various forms for food. It is

either roosted or boiled with its cob and eaten or can be milled to prepare a food locally known

as Moimoi-Oka or Agidi in eastern Nigeria, tuwo or tuozaafi, banku and kenkey in northern

Nigeria and Ghana which are all eaten with soup. Sometimes the grains can be removed from the

cob, dried and later fried or roasted which is mixed with fried groundnut and eaten (Ogbonna,

2014). Some industrial uses of corn include filler for plastics, packing materials, insulating

materials, adhesives, chemicals, explosives, paint, paste, abrasives, dyes, insecticides,

pharmaceuticals, organic acids, solvents, rayon, antifreeze, soaps, and many more. Corn also is

used as the major study plant for many academic disciplines such as genetics, physiology, soil

fertility and biochemistry (Gibson and Benson, 2002).

2.2 Stored Products

Stored products like cereals that can be kept for long periods of time without spoilage are usually

affected by abiotic and biotic factors in the environment (Dobie et al., 1984). Temperature and

moisture content of the cereal grains are the two key factors affecting the resulting quality of the

grain, biochemical reactions, dry matter losses, allowable storage times and overall storage

management of the grain (Gonzales et al., (2009); Lawrence and Maier, (2010)).

2.2.1 Temperature

This can be defined as the degree of hotness or coldness of an environment or any material.

Temperature is probably the most important factor that affects storage insects and other living

organisms in the store (Dobie et al., 1984). Effect of temperature on the produce may bring about

heat generation, this happens because the produce that is being stored is alive and any change in


20

the temperature within certain limit is likely to increase its metabolic activities. It is generally

believed that stored produce contain some amount of heat and during storage, this heat is

released gradually to the surrounding environment. Unfortunately, maize is a poor conductor of

heat therefore in an environment with high temperature fluctuations where the heat is not likely

to be conducted away; condensation may take place and consequently, deterioration of the

maize. (Pixton and Warburton, 1971).

2.2.2 Moisture Content

Biological and biochemical activities occur only when moisture is present. Hence, for safe

storage of grain, both the moisture content of the grain and that of the surrounding air should be

reduced and monitored (Jayas and White, 2003). Maize grains, like other stored products, are

hygroscopic materials (i.e. they absorb and release water). They consist of a constant amount of

dry matter but water content will vary (Devereau et al., 2002). Moisture content plays a

significant role in the storage of grain; when grain has more moisture, it heats up and can have

mold spoilage (Brewbaker, 2003).

Living organisms, such as moulds and insects, and thermal heat produced by respiration of the

grain itself will enhance water vapour, which in turn will lead to further deterioration of the grain

(Wimberley, (1983); Freer et al., (1990)). As a general expression, the higher the moisture

content, the more susceptible the maize grain is to mould and insect deterioration (ACDI/VOCA,

2003).

2.2.3 Relative Humidity

Relative humidity can be described as the amount of water vapour that is contained in the air as a

proportion of the amount of water vapour required to saturate the air at the same temperature


21

Lawrence (2005). Relative humidity affects both the stored products and the biotic components

in the stored product environment. Stored products vary in their tolerance to relative humidity.

Others can survive 0% relative humidity, while others require about 75% or more relative

humidity for optimum growth and development (Obeng-Ofori & Boateng, 2008).

2.2.4 Interactions between Temperature and Relative Humidity

Several studies have been conducted to examine the relationship between temperature and

relative humidity in grain storage in the tropics, and results have revealed a direct relationship

between them. As temperature increases, grain will lose moisture to the surrounding air, thereby

increasing the relative humidity (Devereau et al., 2002). It has been observed that with most

cereal grains, every 10 °C rise in temperature cause an increase of about 3% in relative humidity

(ACDI/VOCA, 2003). Shah et al., 2002, explained that changing temperature and relative

humidity promotes moulds growth, and also causes considerable nutrient losses of grain. For the

case of nutrients, after six months of maize storage at 45 °C and 12 % RH, result showed

significant decreases in protein and soluble sugars, up to 20.4 % (Rehman et al., 2002).

Moreover, according to Samuel et al., (2011), even after drying, maize grain harvested in

tropical countries retained a certain amount of moisture so that when exposed to air, exchange of

moisture between the maize grains and surrounding occur until the equilibrium is reached.

Beside this, fluctuation of temperature and relative humidity in tropical countries accelerates

rapid multiplication of moulds and insects, which facilitate further spoilage of grain (Yakubu,

2009).


22

2.3 Prostephanus truncatus

2.3.1 Taxonomic Tree

Domain: Eukaryota

Kingdom: Metazoa

Phylum: Arthropoda

Subphylum: Uniramia

Class: Insecta

Order: Coleoptera

Family: Bostrichidae

Genus: Prostephanus

Species: Prostephanus truncatus (CABI, 2015).

Prostephanus truncatus was first described in 1878 by Horn as Dinoderus truncatus, and has

been referred to as Stephanopachys truncatus by Back and Cotton (1938). Lesne (1898) erected

the genus Prostephanus and referred them to three other species but only P. truncatus is known

to associate with stored products. The most common English name used for the species is larger

grain borer (LGB). The adult P. truncatus is typically cylindrical in shape with a body length of

3-4.5mm long. Moving down from its head, it is flattened and steep which are terminated

apically and laterally by a carina. It has many small tubercles over its body surface. The antennae


23

are 10-segmented with a loose three-segmented club where the apical club is as wide as or even

wider than the preceding segment.

The Larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) was

accidentally introduced into Africa and its occurrence was first recorded in the Tambora region

of Tanzania in 1981 and later on in Togo (Harnisch and Krall, 1984). It is originally a wood

borer and in its area of origin, it was occasionally reported as a pest of stored maize without

economic importance (Schultess, 1999) but with its introduction to Africa, its global economic

importance drastically changed. It became a serious pest of stored maize and dried cassava

(Markham et al., 1991). It is now distributed over all the major maize producing regions in sub-

Saharan Africa (Adda et al., 1996).

P. truncatus may be attracted to maize grain and dried cassava over short distance. It has been

shown in laboratory tests that upwind flight is mediated by a male-released aggregation

pheromone and not by host volatiles (Fadamiro et al., 1998) and field studies provide strong

evidence that host selection, in the case of maize and cassava, occurs by chance (Birkinshaw et

al.,2002).

Adults frequently initiate their attack on stored maize cobs with intact sheaths by boring into the

base of the maize cob cores, although they eventually gain access to the grain via the apex of the

cob by crawling between the sheathing leaves Adults bore into the maize grains, making neat

round holes, and as they tunnel from grain to grain they generate large quantities of maize dust.

(Hodges and Meik, 1984). Adult females lay eggs in chambers bored at right angles to the main

tunnels. Egg-laying on stabilized grain, like that on the maize cob, is more productive than on

loose-shelled grain as the oviposition period is longer, equal in length to the life of the female,

and the eggs are laid at a greater rate. Larvae hatch from the eggs after about three days at 37°C


24

and seem to thrive on the dust produced by boring adults. For example, large numbers of larvae

develop and pupate in dust at the base of dense laboratory cultures (Hodges, 1986).

The life cycle of P. truncatus was investigated at a range of temperatures and humidity (Shires,

(1980); Bell and Watters, (1982); Hodges and Meik, (1984)). Development of the larva through

to the adult stage at the optimum conditions of 32°C and 80% RH takes 27 days on a diet of

maize grain. Humidity within the range 50-80% RH does not greatly affect the developmental

period or mortality; at 32°C, a drop in RH from 80 to 50% (giving maize with an equilibrium

moisture content of about 10.5%) extended the mean development period by just 6 days and

increased the mean mortality by only 13.3%. This tolerance of dry conditions was confirmed

during field studies in Nicaragua and Tanzania in which maize at 10.6 and 9% moisture content,

respectively, was heavily infested (Golob and Hanks (1990) and Meikle (1998)). The success of

this pest may be partly due to its ability to develop in grain at low moisture. Many other storage

pests are unable to increase in number under low moisture conditions. For example, Sitophilus

oryzae, a species occurring in the same ecological niche, needs a grain moisture content of at

least 10.5% for development. Thus, in dry conditions, P. truncatus probably benefits from the

absence of any significant competition from other storage pests (Subramanyam & Hagstrum,

1995).


25

2.4 Sitophilus zeamais

2.4.1 Taxonomic tree

Domain: Eukaryota

Kingdom: Metazoa

Phylum: Arthropoda

Subphylum: Uniramia

Class: Insecta

Order: Coleoptera

Family: Dryophthoridae

Genus: Sitophilus

Species: Sitophilus zeamais (CABI, 2012).

These occur throughout warm, humid regions around the world, especially in locations where

maize is grown. They are slender insects with a conspicuous snout projecting forward from the

head. They are dark brown, sometimes with four orange spots on the wing covers. They are less

than 3/16 inch long. The female chews through the surface of the grain, creates a hole, deposits a

small oval white egg, and covers the hole as the ovipositor is removed, with a waxy secretion

that creates a plug. Larvae are white, legless, and looked wrinkled and are only found inside

whole kernels or seeds feeding on the grain rendering it useless and unfit for human

consumption. The maize weevil commonly attacks standing crops, in particular, maize before

and after harvest, and is also commonly associated with rice (Longstaff, (1981); Hidayat et al.,

(1996)).

Infestation usually starts in the field and later continues in the store. Both species are capable of

inhibiting reserved breeding grounds near the threshing floors that are normally full of plant


26

residues, where the population builds up in before moving to granaries. Adult females chew

grains creating a small hole in which they lay eggs and then seal the hole with a secretion. The

optimum temperature for oviposition is around 25°C and at grain moisture contents of over 10

percentage (Brich, 1944). Larvae tunnel in grains and are responsible for most of the damage.

Pupation takes place inside the grain and adults chew their way out through the outer layer of the

grain. Adults live for 5-6 months depending on the temperature and humidity of grains.

(Kuschel, (1961); Giles et al., (1969); Mound, (1989)). S. zeamais tolerates lower temperatures

than S. oryzae and can live for 37 days at 0°C (Stoyanova, (1984); Zewar, (1993)). Figure 1 & 2

shows the distribution of S. zeamais and P. truncatus in Africa.

Figure 1: Distribution of S. zeamais in Africa (CABI, 2012).

Key

Presence of S. zeamais


27

Figure 2: Distribution of P. truncatus in Africa (CABI, 2015).

2.5 Post harvest Technology

After maize is harvested, it undergoes several operations, which if not done properly, may result

in serious losses (Laubscher & Cairns, (1983); Jonsson & Kashweka, (1987); Gwinner et al.,

(1996)). Whole grain is an essential item for successful storing. Damage or cracks to grains may

happen due to improper application of post-harvest practices such as threshing, drying or

transporting (Rowley, (1984); Simone et al., (1994)). These cracks can serve as entry points to

insects or moulds infestation.

Food security can be assured by improving on post-harvest storage methods. Food stored under

improper storage conditions are prone to increased respiration and transpiration processes which

often result in depletion and weight loss of edible material. Storage temperature and relative

humidity are major factors that ultimately determine product quality and quantity (Adeyinka et

al., 2011)

Key

Presence of P. truncatus Widespread of P. truncatus P. truncatus is localized


28

Spoilage of food products is due to activity of insects or microorganisms or due to biochemical

and physical changes in foods (Frazier & Westhoff, 1978). Various food preservation methods

have been developed over the years. Generally, chemicals were used to control the activity of

insects or microorganisms in food. An increased awareness by the environmental and health

agencies and consumers of the harmful chemical residues in food and environment led to the

restricted use of chemical preservatives in food (Calderon, 1980). Grains are usually dry and

cannot support the growth of bacteria (Jay, 1992). Insects and moulds are major spoilage

organisms in stored-grain ecosystems and are aerobic in nature. Therefore, creating an anoxic

atmosphere in the stored-grain ecosystems has a lethal effect on insects and moulds and extends

the storage life considerably. The effectiveness of modified atmosphere in controlling insects is

dependent on various abiotic (gaseous composition, relative humidity, temperature, length of

exposure and gas pressure) and biotic (insect species, life stage and the size and distribution of

infestation) factors. All these factors must be optimized to create an environment which is lethal

to the insect species found in the stored grain (Midwest Plan Service, 1998).

Storage structures and systems can be divided into two, traditional systems and modern systems.

Traditional methods vary from storing on the floor to storing in the crib; modern methods vary

from the small drum and bags to the complex silo. The storage arrangements and methods

currently in use in many societies are the result of age-old experience and tradition and have

become perfectly suited to local conditions (Bani & Josiah, 2008).

When dried to moisture contents below the safe moisture level, cereals and pulses can be stored

for periods of a year or more under a wide range of temperatures, provided that during storage

the moisture level does not rise, and precautions against insects are taken; insects may still


29

develop at a relative humidity of approximately 35% and temperatures of around 15°C. Often the

products are dried in the field as much as possible (Dobie et al., 1984).

During pre-storage drying period, and sometimes even before harvesting, the products may

easily become infested with insects. When the products have reached the safe moisture content,

they can be stored permanently. Often they will be threshed first, as the threshed product takes

up less storage space. Even if the product is still too moist, it can be stored, and during storage, it

can dry further. This will require very good ventilation. If necessary, they may be threshed when

the safe moisture level has been reached and they can then be stored in a less voluminous and

better protected way (Obeng-Ofori & Boateng, (2008); Bani, (2008)).

2.5.1 Methods of storage

The type of foodstuff and the size of the crop to be stored determine the design and capacity of

these facilities. Farmers store their crops either outside, suspended or on platforms, or in

granaries, or even inside their homes.

2.5.1.1 Cribs

A distinct improvement on platforms, a crib has ventilated sides made of bamboo grass stalks or

even wire netting. The length of crib should be perpendicular to the prevailing wind direction. In

humid countries where grain cannot be dried adequately prior to storage and needs to be kept

well aerated during the storage period, traditional granaries (cribs) are usually constructed

entirely out of plant materials. This includes timber, reeds and bamboo which provide good

ventilation. Storage cribs made of wood and chicken-wire have been introduced by NGOs. These

worked well in Rwanda and rural parts of Uganda but were rejected by farmers in Kenya because

the sides made of chicken wire made the contents visible and were easy to steal from (FAO,

1985; Appert, 1987)


30

Plate 1: A Bamboo Crib

(ehp.niehs.nih.gov/121-a270 7/3/15 6:47pm)

2.5.1.2 Banco/Mamrusi/Kusasi/Rumbu Granaries

In some parts of Africa, such as Morocco, Mauritania, Nigeria, Chad, Cameroon and

Somalia, grains are stored underground ( Bartali et al., 1990; Bakhella et al., 1993;

Lemessa & Handreck, 1995). These granaries are made of clay which is sometimes mixed with

fragmented plant materials (grass, twigs). In some cases the clay comes from termite mounds.

They may also be constructed with clay bricks. They are insulated from the ground by means of

wooden poles, clay pedestals or large stones. They may be either circular or rectangular in shape;

in the latter case the inside may be partitioned off into separate compartments.

Some are more or less round with the tip pointing downwards and resting on stones. Such

granaries are common in Chad, Mali, Mauritania and Niger. They are a cheap means of storage


31

and well suited to the dry climate of these countries. While some are quite small, others have a

capacity of up to 5 tons. Because they can be hermetically sealed, insects are unable to penetrate

and find it difficult to develop even if they manage to get inside because of reduced oxygen

(Bartali et al., 1990; Bakhella et al., 1993; Lemessa & Handreck, 1995).

The complete lack of ventilation means moisture content of the grain must not exceed 10% and

the humidity must be less than 70%. These granaries are not resistant to persistent or heavy

rainfall and care must be taken to seal up promptly the cracks which easily form with this type of

material ions. Each type of grain storage arrangement must undergo continued improvements in

order to give commodities the greatest protection against pests and adverse environment (CIGR

1999).

Plate 2: Traditional maize storage systems in the southern region of Togo (Pantenius, 1988) (A: not-heated granary; B: Regularly heated in house storage; C: Irregularly heated

granary)


32

Modern structures should be designed such that they meet certain basic requirements with

regards to location, accessibility and use.

2.5.1.3 Metal Silos

Metal silos (including recycled oil drums) have emerged as efficient and low cost storage

containers for the storage of cereal grains and pulses. Inaccessible by rodents, efficient against

insects, sealed against entry of water, drums make excellent grain containers. However they

should be protected from direct sunshine and other sources of heat. To avoid condensation they

should be located in shaded and well ventilated places (Christensen 1974; Villers et al., 2008).

2.5.1.4 Warehouses

Warehouses are built for storage of physical protection of produce. The deterioration of stored

crops can be reduced by restraining attack by arthropods and rodents through the control of

moisture and temperature. In the design of warehouse, the following points must be seriously

adhered to:

1. Any gap between the roof and the walls should be sealed with a solid material such as cement

or sand to prevent entry of birds and other pests.

2. All pipes, shafts and ducts should be sealed against the entry of rodents

3. Partition walls must be of solid construction and well-sealed to the main walls

4. Stores must be simple in design with smooth internal projections. This will prevent

accumulation of spillage that forms local points for insect infestation.

5. Walls and roofs of store must be of solid unbroken material and easily sealed to ensure easy

fumigation

6. Doors and windows should be kept to a minimum number and must be tight fitting

7. Development of cracks in the store should be prevented (CIGR, 1999).


33

2.6 Hermetic storage

2.6.1 Postcosecha galvanized steel silos

The Postcosecha galvanized steel silo was developed in Central America in about 1980 for on-

farm storage of grain and seed. Postcosecha (postharvest in Spanish) is a development

programme begun in Honduras in the 1980s, which has evolved into a technology production

and dissemination organization operating in Central America and elsewhere in developing

countries. The Swiss Agency for Development and Cooperation supported the original silo

construction programs in El Salvador, Nicaragua, Honduras, and Guatemala where nearly

600,000 silos were built by 2008 (Bravo-Martinez 2008).

Postcosecha silos are built locally using simple tools, 26-gauge (0.7-mm) galvanized steel sheets,

and lead-based solder. Grain capacities range from 180 to 1360 kg (7 to 53 bushels).

Joints and seams use a 5-mm fold, which is crimped and soldered for strength and tightness. A

37-cm-diameter intake throat is built into the top of the silo for filling and inspection. The throat

protrudes about 10 cm above the top and is fitted with a snug-fitting removable cap. A 15cm

diameter outlet port for removal of grain is located with its centre 10.5 cm above the floor. It

protrudes about 15 cm and is also fitted with a snug fitting removable cap. The intake throat and

outlet port caps can be sealed with locally available products such as tallow, grease, soft soap,

beeswax, or a bicycle tire inner tube strip (SDC 2013).

Bulk products such as maize, beans, sorghum, rice, wheat, barley, as well as seeds can be stored

in silos. The product must be clean and dry (below 14% moisture for maize) before being placed

in the silo to prevent fungal spoilage. The silo has no provision for mechanical aeration. At the

farm the silo is placed on a 15-cm-tall wood platform in the shade, under a roof, or inside the

house. The outlet port allows small quantities of maize to be removed as needed for food


34

Postcosecha silos are built locally and sold to farmers by persons called “artisans.” These

artisans complete a short course covering all elements of building and selling silos. A 159-page

publication covering all technical and business aspects of silo construction is available in several

languages (SDC 2013). Local employment and commerce generated by silo construction is an

important benefit of the Postcosecha development program. Storing grain in a silo also allows

farmers to market surplus grain when prices are high, instead of at harvest when prices may be at

yearly lows.

If clean maize at 14% moisture or below is placed in a silo and managed properly, losses during

one year or more of storage will be near zero. If the silo is filled with maize and hermetically

sealed, maize weevils and other insects will be kept under control. Insecticide tablets (Phostoxin,

Detia, Quick Phos, Gastion) are also available for chemical control of insects in the silo. There is

evidence that the caps on these silos often are not sealed well enough to kill insects due to lack of

oxygen and insecticide tablets need to be used to keep the grain insect free (GrainPro Inc. Latino

America 2010).

Silos have an expected life of 25 to 40 years, with proper maintenance (Sieber 1999). Silos

reportedly pay for themselves because of higher market process obtained for stored grains losses,

which are traditionally over 20% of the harvest (Rodriguez-Corea 2011).

2.6.2 Polyethene bags

Polyethylene (PE) is a widely used semi-crystalline polymer with a range of applications in

packaging, house wear, sporting goods, and biomedical uses, among several others.

By varying the catalyst and/or the polymerization process, polyethylene can be obtained having

markedly different chain structures, solid-state structures and physical mechanical properties

(Peacock, 2000). Based on molecular structure, the polyethylene is divided into four different


35

types. The linear or high-density polyethylene (HDPE) contains no short chain branching (SCB)

or a very small fraction of SCB. Copolymerization of ethylene with a 1-alkene type co-monomer

yields polyethylene with a larger fraction of SCB, the so-called linear low density polyethylene

(LLDPE). High-pressure homopolymerization (LDPE) or copolymerization of ethylene in

tubular reactors leads to polyethylene and ethylene copolymers with both types of branching,

SCB and long chain branching (LCB). Apart from the interplay between molecular variables and

the resulting crystalline structure after processing, understanding the basic deformation

mechanisms has also been a subject of intense interest (Lin et al., 1994).

2.6.2 Purdue Improved Cowpea Storage (PICS) System

A team at Purdue University has developed the Purdue Improved Cowpea Storage and is

promoting its use in Western Africa with funds from the Gates Foundation. The programme uses

a triple plastic bagging system developed by entomologist Larry Murdock (Forbes, 2007). The

PICS system was developed for storage of cowpeas in West and Central Africa and the project

goal was aimed at having 50% of the farm-stored cowpea in hermetic storage without

insecticides by 2012 (Baribusta et al., 2010).

PICS technology uses plastic bags to achieve hermetic storage of cowpeas and other grains.

Threshed cowpea grain, dried to an appropriate moisture level and free of crop debris, is placed

into 50- or 100-kg capacity high-density polyethylene bags with 80-μm thickness. A first bag is

filled completely, but with a 20- to 30-cm neck, which is tied securely. Then, this bag is

surrounded by a second bag with the same thickness. The second bag’s neck is also tied securely.

Finally, these two bags are placed in a third woven nylon or polypropylene bag used for its

strength. With the third bag tied securely, the container can be handled without bursting the inner

bags, and is readily accepted by grain handlers who are accustomed to handling cowpea in this


36

type of woven bag. Over the past three years, over one million bags have been produced and sold

through this program (Baributsa et al., 2010). The cost for two 100-kg polyethylene bags and one

outer bag averages $3. Life is about two years (Baributsa 2011).

2.6.3 GrainPro ultra-hermetic bags

GrainPro Inc. of Concord, Massachusetts, USA manufactures and markets an extensive line of

ultrahermetic bags designed to achieve hermetic storage conditions. The bags are used to store a

wide variety of agricultural commodity products and also many types of seeds, and are marketed

Worldwide (Villers et al., 2010).

The SuperGrainbag IIITM is a type suitable for use by the small farmer to store maize on the

farm. It is available with capacities of 30 to 100 kg of maize. Besides maize, it is applicable for

coffee, paddy, milled rice, sorghum, millet, soybeans, wheat, cocoa, beans, peas, lentils, and all

types of seeds. Product is placed in the 78-μm multilayer polyethylene bag with a proprietary

barrier layer that makes its permeability to oxygen far lower than polyethylene alone. It uses a

two-track zipper and is sealed using a zipper slider. The sealed bag is then placed in a protective

woven outer bag. The SGB IIITM membrane has an oxygen transmission rate of 4.28 cm3m-

2day-1 and a water vapor permeability of 2.14 g cm-2day-1. The 70-kg bag costs $2.50 +

shipping in 200-bag lots (GrainPro 2013). Outer protective bags cost about $1US. Maize can be

stored for up to two years in a storage cycle. With careful use, the bag will last for about five

cycles. Punctures can be repaired with tape (Villers 2013).

2.7 Practical Hermetic Storage

Previous research studied the effects of temperature, time, and maize moisture and oxygen levels

on maize weevil mortality (Yakubu et al., 2011). Weevil infested on commercial hybrid maize

grain sampled in 476-mL (1 pint) jars were held under hermetic conditions at maize moisture


37

levels of 6.3% and 16%, and at two levels of temperature, 10°C and 27°C. The hermetic

conditions were effective in killing weevils. There were significant effects due to temperature

and moisture content. Equations were developed to predict the time to 100% adult weevil

mortality as a function of temperature, maize moisture content and initial oxygen volume.

Another work studied the effectiveness of hermetic triple layer biodegradable bags (HTLBB) and

polypropylene interwoven bags (PIB) in reducing losses of stored maize (Ansah et al., 2014).

Experiments were conducted in a small holder farmer storage crib and in the laboratory where

factorial combination of HTLBB, PIB and maize varieties, improved Obatanpa and local Denkye

were used. The samples were stored for six months at an average temperature of 27oC and 58 %

R.H. The moisture content, hidden infestation, weight loss, germination capacity and colour were

assessed. A significant increase in the moisture content of both varieties (12.4% - 15.4%) was

found in HTLBB- stored samples probably due to airtight conditions and the respiratory

activities of grains, while in PIB no significant differences were found (12.4% - 12.9%).

Laboratory and field assessment of percentage germination and emergence was higher in

Obatanpa than in Denkye. However, HTLBB-stored samples, kept 90% of germination capacity

while in PIB-stored, a maximum of 60%. Weight losses were also lower in HTLBB-stored

Obatanpa and Denkye at 7.4% and 3.8% than PIB-stored at 15.1% and 9% respectively,

attributable to varietal type and hidden infestation.

A study was carried under ambient laboratory conditions of 32± 2oC and 72-88% r.h to

determine the effectiveness of the triple-layer hermetic bag in controlling the maize weevil

Sitophilus zeamais (Mot) on three varieties of maize (Obatampa, Abrodenkye and

Kamangkpong) (Anankware et al., 2012).


38

In the experiments, five (5) kilograms of each variety with three replicates were infested with 50

S. zeamais and stored for three months in three different types of bags (hermetic, Polypropylene

and Jute). Sampling was carried out monthly to determine the moisture content, seed viability of

each variety and weight loss after storage. Percentage damage of grain due to S. zeamais was

assessed on the different types of storage bags. The results showed that the high yielding

Obatampa was more susceptible to S. zeamais than the two local varieties; Abrodenkye and

Kamangkpong. Damage, weight loss and germination rates were significantly higher in the

polypropylene and jute bags than the hermetic bags. These were also dependent on the length of

storage. It was established that the triple-layer hermetic bags were effective against S. zeamais

and could be used for storage of maize (Anankware et al., 2012).

Other hermetic storage systems in use include double and triple plastic bags (Murdock et al.,

2012; Baoua et al., 2013; Murdock and Baoua, 2014;), which are being used to store cowpeas in

West Africa. This technology requires substantial operational involvement and associated skill to

achieve air-tightness. Experience may be necessary to achieve good results and hermetic

conditions are not guaranteed. It is difficult to maintain a sealed system for a long period of time,

and moulding of grain could occur where moisture has accumulated in the storage bags

(Caddick, 2007). While bagging may be to some extent effective in killing insects, it doesn’t

provide mechanical protection against rodents and the bag usually has no more than two years of

useful life (Bern et al., 2013). Barrels provide mechanical protection and are of a size useful to

many smallholder farmers.


39

CHAPTER THREE

3.0 MATERIAL AND METHODS

3.1 Study Site

The study was carried out in the laboratory of the African Regional Postgraduate Programme in

Insect Science (ARPPIS) and at the Entomology laboratory of the Crop Science Department of

the University of Ghana, Legon in the Greater Accra Region of Ghana from June 2014 to May

2015.

3.2 Sources of Experimental Materials

3.2.1 The maize

Local Maize variety (Abrodenkye) was used for the experiment. Nine (9) bags (150 kilogram

sized bags) of the maize were purchased at Madina market. The moisture content was

determined using Protimeter (Digital Grainmaster).

3.2.2 The Triple Layer Hermetic Bags

The Triple layer hermetic bags of five (5) kilograms capacity were developed and supplied by

Bio-Plastics Limited, Ghana free of charge. The five (5) Kg capacity was used in order to

minimize space. Each triple layer bag had two plastic bags with high density (300µm) inserted

into a polypropylene interwoven bag to give additional protection and strength.

3.2.3 Culturing the Insects

The insects Sitophilus zeamais and Prostephanus truncatus were obtained from

VESTERGARD/ARPPIS Insectary University of Ghana, Legon, Accra. They were reared at


40

culture conditions of 28 ± 2oC, 65% relative humidity and 12L: 12D photo regime (Weaver et al,

1994; Osafo, 1998). The insects were then introduced to sterilized maize in a plastic container

covered with a muslin cloth and fastened by a rubber band. The grains were sterilized in an oven

at 60 ºC for 6 hours to kill the eggs of insects and microbes that could be present on the grains.

The insects were left in the container for two weeks to oviposit and make a colony. Parent stock

were sieved and removed so that new generation of same age will emerge and be used for the

research work.

3.2.4 Temperature Regulators

Temperature was regulated using RUMED incubator at the entomology laboratory in Crop

Science Department to get 18˚C and room heaters obtained from VESTERGARD laboratory to

get 38˚C used for the experimental work.

3.3 Laboratory experiments

3.3.1 Experimental design

A 3x2x2 factorial experiment was carried out in a completely randomized design. There were

three different temperatures (38oC, 18oC and room temperature which ranges from 27-32oC

throughout the period of the experiment). Two storage bags were used, the triple layer hermetic

bag and polypropylene bag. P. truncatus and S. zeamais were the two insects species used to

infest the maize for the experiment. Table 1 shows the different treatment combinations as would

be discussed in the results.


41

Table 1: Acronyms for the different treatment combinations

Acronym Description

TH38 P. trun

Triple layer hermetic bag at 38 oC infested with P. truncatus

TH38 S. zea

Triple layer hermetic bag at 38 oC infested with S. zeamais

Poly38 P. trun

Polypropylene bag at 38oC infested with P. truncatus

Poly38 S. zea

Polypropylene bag at 38oC infested with S. zeamais

TH18 P. trun

Triple layer hermetic bag at 18 oC infested with P. truncatus

TH18 S. zea

Triple layer hermetic bag at 18 oC infested with S. zeamais

Poly18 P. trun

Polypropylene bag at 18oC infested with P. truncatus

Poly18 S. zea

Polypropylene bag at 18oC infested with S. zeamais

THRT P. trun

Triple layer hermetic bag at room temperature infested with P.

truncatus

THRT S. zea

Triple layer hermetic bag at room temperature infested with S.

zeamais

PolyRT P. trun

Polypropylene bag at room temperature infested with P. truncatus

PolyRT S. zea

Polypropylene bag at room temperature infested with S. zeamais

MCH38

Moisture content in triple layer hermetic bag at 38oC

MCP38

Moisture content in polypropylene bag at 38oC

MCH18

Moisture content in triple layer hermetic bag at 18oC

MCP18

Moisture content in polypropylene bag at 18oC

MCHRT

Moisture content in triple layer hermetic bag at room temperature

MCPRT

Moisture content in polypropylene bag at room temperature


42

3.3.2 Effect of Temperature on the Efficacy of the Triple Layer Hermetic Bag

A factorial experiment was carried out with three (3) different temperatures, two (2) types of

storage bags and two (2) different insects over the period of six (6) months. Five (5) kilogram of

grains were placed into the triple layer hermetic and polypropylene bags and each bag was

replicated three (3) times for each of the three (3) temperature conditions (38oC, 18oC and room

temperature (27-32oC) ). Fifty (50) unsexed P. truncatus were introduced into the bags and were

tied and stored for six months. Another set of five (5) kg of grains were placed in the triple layer

hermetic and polypropylene bags each with 3 replicates, fifty (50) unsexed Sitophilus zeamais

introduced into the bags containing the grains and kept for six (6) months. There were eighteen

(18) bags of each triple layer hermetic bag infested with P. truncatus and 18 infested S. zeamais

for each temperature regime. Likewise, 18 bags of the polypropylene P. truncatus infested grains

and 18 of S. zeamais infested bags of maize which gave a total of 72 small bags as experimental

unit for each of the temperature regime. Each of the triple layer bags had a corresponding

polypropylene bag as its control and this gave rise to 216 experimental units. Sampling without

replacement and destructive sampling were carried out every month to determine the weight loss,

percentage damage and oxygen depletion level. Germination potential (seed viability) was

carried out at the start and at the end of the six months storage period for the different

temperature regimes.

3.3.3 Procedure for Determining Weight Loss

The Thousand Grain Mass (TGM) method (Boxall, 1986) was used to determine the percentage

weight loss. This was done monthly for the period of six (6) months.

Method;


43

1. 1kg of sample was collected and sieved to remove all unwanted material to obtain a working

sample.

2. A sub sample of the working sample was obtained and the moisture content was measured.

3. The grains of the sub sample was weighed and counted and the TGM calculated as follows:

TGM = 10W (100-MC)/N

W = wet weight of sample;

MC = moisture content (wet weight basis)

N = number of grains in the sample.

Percentage weight loss will then be:

Percentage (%) weight loss = (M1-Mx)/M1 x 100

Where;

M1 = TGM of the grain at the start of storage

Mx = TGM of the grain at the time x

3.3.4 Determining Rate of Oxygen Depletion

Oxygen depletion rate was assessed using a SCY-2A oxygen analyser (Plate 3), butterfly needles

and epoxy glue to test for the presence of oxygen in the triple layer hermetic storage bag. The

butterfly needle was used to puncture the triple layer bag after it has been tied and the needle was

fastened to the bag using the epoxy glue. This was done to prevent the air from entering the bag

through the hole created by the needle and also to prevent the needle from falling off. The

oxygen analyser was connected to the needle inserted in the bag through a tube and it was


44

switched on to take the reading of the oxygen in percentage. This procedure continued from the

start of the experiment until the lowest percentage of oxygen was recorded.

Plate 3. SCY-2A Oxygen Analyser

3.3.5 Determination of Changes in the Tensile Strength of the Hermetic Bags

Tensile strength of the polyethene of the triple layer hermetic biodegradable bags was

determined and observed for changes every 60 days under different temperature (38˚C, 18˚C and

room temperature (27-32˚C)) with a Hounsfield texture analyser (Plate 4). Each of the polythene

was cut into a recommended piece (1cm wide and 15 cm long). 25 pieces of the said dimension

were collected from each polyethene and fixed on the machine to determine its tensile strength.


45

Plate 4: Hounsfield Texture Analyser

3.3.6 Determination of number of live insects found

Each set up was monitored periodically (after every one month) to check the number of live

insects in each type of storage bag. This was done continuously to determine when 0 insect will

be recorded in the hermetic bags under different set up and in the polypropylene bags due to

extreme temperature. A sample was picked from each bag as a representative of the whole,

sieved and the number of live insects counted.


46

3.3.7 Determination of Seed Viability

The seed viability test was conducted before and after storage (six months of storage). The

results of these two were then compared to see if storage in the triple layer hermetic bag under

different temperatures has any effect on seed viability. 90 seeds were randomly taken from the

various bags and planted in experimental pots at the crop science botanical garden. They were

observed for seven days to check for emergence.

The seed viability or germination potential was calculated using the formula:

Germination potential, Gp = Ng/Nt × 100

Where

Ng = number of germinated seeds

Nt = total number of seeds in the sample or initial number of seeds in sample

3.3.8 Data Analysis

Data was collected and analysed using Analysis of Variance. The computer software GenStat

12th edition was used to analyse the data.

Where necessary, data involving counts was transformed using log transformation.

log (X+1) where X is the actual value.

Bonferrori test was used to separate means and the level of significance was (p<0.001) from the

GenStat 12th edition.


47

CHAPTER FOUR

4.0 RESULTS

4.1 Moisture Content Variations in the moisture content were significantly different among the types of storage bags

and between treatments in the bag-month interaction (Table 2). The mean moisture content in the

38˚C treatments increased gradually from start of storage to month 2 reduced slightly in month

three (3) & four (4) and remained fairly constant towards the end of the storage period in month

five (5) and six (6) (Figure 3). The same pattern occurred in the maize stored under room

temperature (27-32 ˚C). However, in the 18 ˚C treatment, mean moisture content among the

different storage bags was not significantly different (Table 2). The moisture content in both

storage bags was fairly constant throughout the storage period (Figure 3). The mean moisture

content after six (6) months of storage in the 38˚C treatment were 17.66% and 11.66% in triple

layer hermetic bag and polypropylene bag respectively (Table 2). In the room temperature (27-

32˚C), mean moisture content recorded after six (6) months of storage were found to be 16.5% in

triple layer hermetic bag and 12.7% in polypropylene bag showing significant difference (Table

2). In the 18˚C treatment, 12.30% moisture content was recorded in the maize stored in hermetic

bag after six (6) months while 11.96% was recorded in the polypropylene stored maize which

showed no significant difference (Table 2). The least mean moisture content was recorded in the

polypropylene bags of the following temperature treatments, 38 ˚C (11.96%), 18˚C (12.7%),

room temperature (27-32˚) (11.66%) and in the hermetic bag at 18˚C (12.30%). The highest

mean moisture content was recorded in the triple layer hermetic bags at 38 ˚C (16.75%) and

room temp. (27-32˚C) (17.66%) temperature conditions (Table 2).


48

Table 2: Mean moisture content for six (6) months in different treatment combinations

Treatment Combinations

Mean % moisture content SE of means

MCH38

16.75 c 0.086

MCP38

11.96 ab 0.145

MCH18

12.30 ab 0.107

MCP18

12.70 b 0.173

MCHRT

17.66 c 0.137

MCPRT

11.66 a 0.450

*a-c: In case where superscript in the same column do not share the same letter, they are significantly different (p>0.001). Multiple comparisons with Bonferroni test.

**MCH38= Moisture content of maize stored in hermetic bag at 38oC; MCP38= Moisture content of maize stored in polypropylene bag at 38oC; MCH18= Moisture content of maize stored in hermetic bag at 18oC; MCP18=Moisture content of maize stored in polypropylene bag at 18oC; MCHRT =Moisture content of maize stored in hermetic bag at room temperature; MCPRT= Moisture content of maize stored in polypropylene bag at room temperature


49

Figure 3: Moisture content of maize in triple layer hermetic and polypropylene bags in

three (3) different temperature conditions. *MCH38= Moisture content of maize stored in hermetic bag at 38oC; MCP38= Moisture content of maize stored in polypropylene bag at 38oC; MCH18= Moisture content of maize stored in hermetic bag at 18oC; MCP18=Moisture content of maize stored in polypropylene bag at 18oC; MCHRT =Moisture content of maize stored in hermetic bag at room temperature; MCPRT= Moisture content of maize stored in polypropylene bag at room temperature. Lsd (p>0.05).

0

5

10

15

20

25

1 2 3 4 5 6 7

% m

oist

ure

cont

ent

Duration (months)

MCH38

MCP38

MCH18

MCP18

MCHRT

MCPRT


50

4.2 Effect of temperature on the tensile strength of the polyethene bag

At the start of the experiment, the tensile strength of the polythene bag used for hermetic storage

and the figure below shows the result obtained. The linear portion of the curve is the elastic

region (proportionality limit) and the slope is the modulus of elasticity. After the yield point, the

curve typically decreases slightly because of dislocation. The yield point is the stress or force at

which a material begins to deform, at this point, the material can go back to its original shape if

the stress is removed but when it the yield point is passed, some fractions of the deformation will

be permanent and non-reversible. As deformation continues, the stress increases on account of

strain hardening until it reaches the ultimate tensile strength.

Figure 4: Tensile strength of polythene at the start of storage.

*Ext= extension measured in millimeter; force = force measured in Newton

y = 0.6822x + 11.581R² = 0.9373

0

5

10

15

20

25

30

35

1 5 9 13 17 21 25

Forc

e (N

)

Extension (mm)

ForceExtLinear (Force)


51

Figure 5: Tensile strength of polythene after 60, 120 and 180 days under storage

temperature 38˚C

y = 0.6822x + 11.581R² = 0.9373

y = 0.8001x + 10.263R² = 0.9518

y = 0.8847x + 17.203R² = 0.9804

y = 0.934x + 14.188R² = 0.9308

0

5

10

15

20

25

30

35

40

45

1 5 9 13 17 21 25

Forc

e (N

)

Extension (mm)

0 Days 60 Days 120 Days 180 Days


52

Figure 6: Tensile strength of polythene after 60, 120 and 180 days under 18oC storage temperature

y = 0.6822x + 11.581R² = 0.9373

y = 0.9627x + 16.347R² = 0.9962

y = 0.7159x + 11.536R² = 0.9452

y = 0.7197x + 11.487R² = 0.9552

0

5

10

15

20

25

30

35

40

45

1 5 9 13 17 21 25

Forc

e (N

)

Extension (mm)



53

Figure 7: Tensile strength of polythene after 60, 120 and 180 days under room temperature

y = 0.6822x + 11.581R² = 0.9373

y = 0.5418x + 7.0176R² = 0.9552

y = 0.5994x + 8.7661R² = 0.9769

y = 0.6409x + 9.6323R² = 0.9775

0

5

10

15

20

25

30

35

1 5 9 13 17 21 25

Forc

e (N

)

Extension (mm)



54

Table 3: Yield point of tensile strength of polythene material as represented on the graph

Treatments R-value Slope

Days Temperature (point at which deformation starts)

0 - 0.968 0.6822x + 11.581

60 38 0.983 0.8001x + 10.263

18 0.998 0.9627 + 16.347

Room temperature 0.977 0.5418x + 7.0176

120 38 0.990 0.8847x + 17.203

18 0.972 0.7159x + 11.536


180 38 0.965 0.934x + 14.188

18 0.977 0.7197x + 11.487


*There was a highly positive correlation according to the values

From the slope and the R-value, the polythene material stored at room temperature at 180 days

has the highest correlation between force exerted and yield point of the material which means

that less force was required to break the material as it became brittle. However, more force was

required to break the polyethylene materials stored at 38 oC after six months. Graphical

representation is shown on Figures 5, 6 and 7 for the three temperature (38 oC, 18oC and room

temperatue) conditions respectively.


55

4.3 Result and analysis of Weight loss

Significant difference (p< 0.001) in weight loss of grains stored in both triple layer hermetic bag

and polypropylene interwoven bag was recorded under the different temperature conditions set

up for the experiment. In the case of the 18 ˚C temperature condition, there was a significant

difference in weight loss between grains stored in triple layer hermetic bag and the

polypropylene stored grains infested with both P. truncatus and S. zeamais. In the case of S.

zeamais infested maize, percentage weight loss of 0.41% was recorded in the triple layer

hermetic bags and 0.20% in polypropylene storage bag while 1.21% and 19.42% weight loss of

P. truncatus infested grains was incurred in triple layer hermetic bag and polypropylene bag

respectively as shown in Figure 8.

In another case of 38 ˚C temperature condition, percentage weight loss recorded in S. zeamais

infested maize in triple layer hermetic bag and polypropylene bag were 13.58% and 18.46%

respectively showing no significant difference likewise in the case of P. truncatus infested grains

in both storage bags which recorded 16.62% weight loss in triple layer hermetic bag and 20.12%

in polypropylene bag. (Fig 8)

In the grains stored under room temperature (27-32 ˚C), there was a significant difference in

percentage weight loss of maize between the grains stored in the two storage bags in the case of

P. truncatus infested maize with 16.94% loss in triple layer hermetic bag and 28.15% weight loss

in the polypropylene bag. However, no significant difference was recorded in terms of weight

loss between the two bags in S. zeamais infested maize (Fig 8). The summary of statistics is

shown in Table 4.


56

Figure 8: Mean weight loss of maize for six months of storage.

*least significant difference with significant difference (P>0.001)

0

5

10

15

20

25

30

35%

wei

ght l

oss

Treatment combinations


57

Figures 9, 10 and 11 show the successive percentage weight losses of maize at temperatures

38oC, 18oC and room temperatures respectively while Figure 8 shows mean weight loss for all

treatment combinations over six (6) months

Figure 9: Cumulative increase in % weight loss over the six (6) months storage duration at 38 oC

*TH38 P. trunc= triple layer hermetic bag infested with P. truncatus at 38 oC; Poly38 P. trunc= polypropylene bag infested with P. truncatus at 38 oC; TH38 S. zea=triple layer hermetic bag infested with S. zeamais at 38 oC; Poly38 S. zea= polypropylene bag infested with S. zeamais at 38 oC

0

5

10

15

20

25

30

35

1 2 3 4 5 6

% w

eigh

t los

s

Duration (months)

TH38 P. trun

Poly38 P. trunc

TH38 S. zea

Poly38 S. zea


58

Figure 10: Cumulative increase in % weight loss over the six (6) months storage duration at 18 oC

*TH18 P. trun= P. truncatus infested hermetic bag at 18oC; Poly18 P. trun =P. truncatus infested hermetic bag at 18 oC; TH18 S. zea =S. zeamais infested hermetic bag at 18 oC; Poly18 S. zea= S. zeamais infested hermetic bag at 18 oC. (p>0.001)

0

5

10

15

20

25

30

35

1 2 3 4 5 6

% w

eigh

t los

s

Duration (months)

TH18 P. trun

Poly18 P.trunTH18 S. zea

Poly18 S. zea

loc


59

Figure 11: Cumulative increase in % weight loss over the six (6) months storage duration at (27˚C-32˚C) storage condition

*RTH S. zea=S. zeamais infested hermetic bag at room temperature; RTH P. trun =P. truncatus infested hermetic bag at room temperature; RTP P. trun= P. truncatus infested polypropylene bag at room temperature; RTP S. zea= S. zeamais infested polypropylene bag at room temperature. LSD=(p>0.001)

0

5

10

15

20

25

30

35

40

45

1 2 3 4 5 6

% w

eigh

t los

s

Duration (months)

RTH P. trunRTP P. trunRTH S. zeaRTP S. zea


60

Figure 12: Cumulative increase in % weight loss of maize stored at different temperature conditions in triple layer hermetic and polypropylene storage bags over period of six (6) months

*TH38 = triple layer hermetic bag at 38 oC; Poly38 = polypropylene bag at 38 oC; TH18 = triple layer hermetic bag at 18 oC; Poly18 = polypropylene bag at 18 oC; TH RT = triple layer hermetic bag at room temperature; Poly RT = polypropylene bag at room temperature Lsd bars (p>0.05)

0

5

10

15

20

25

30

35

40

45

1 2 3 4 5 6

% w

eigh

t los

s

Duration (Months)

TH38

Poly38

TH18

Poly18

TH RT

Poly RT


61

4.4 Number of live insects

A highly significant difference (p<0.001) was recorded in the number of live insects of both

species found in both storage bags and under different temperature conditions. In the case of S.

zeamais, the least mean number of live insects was recorded in the triple layer hermetic bag

under room temperature and 38 ˚C temperature condition at an average of 1 insect per kilogram

of maize and the highest mean number of S. zeamais was recorded in polypropylene bag under

room temperature and 18 ˚C temperature conditions which were 2,209 and 610 live insects

respectively. (Figure 13)

There was also a significant difference (p<0.001) in the bag-insect-temperature interaction in the

case of P. truncatus number of live ones after six months of storage. The least mean number of

live P. truncatus found was recorded in the triple layer hermetic bag under room temperature and

38 ˚C temperature condition, both of which were recorded at an average of 1 insect per 1

kilogram of maize. Highest mean numbers were recorded in polypropylene storage bags stored

under the three different temperature conditions. The results obtained were 1,420, 664 and 1105

for 38 ˚C temperature condition, 18 ˚C temperature conditions and room temperature condition

respectively. (Figure 13)


62

Figure 13: Mean number of live insects in different storage bags under different

temperature conditions after six (6) months of storage.

0

500

1000

1500

2000

2500

38HS.

zea

38HP.

trun

38PS.

zea

38PP.

trun

18HS.

zea

18HP.

trun

18PS.

zea

18PP.

trun

RTHS.

zea

RTHP.

trun

RTPS.

zea

RTPP.

trun

Num

ber

of li

ve in

sect

s



63

Table 4: Means and standard errors of differences for weight losses and number of live insects

Treatment Combinations

Mean number Of live insects

S. E of means Of live insects

Mean % weight Loss of maize

SE of means Of % weight

loss

TH38 P. trun

(1.7) 0.463 a 0.167 16.62 b 0.797

TH38 S. zea

(3.9) 0.352 ab 0.124 14.27 b 1.850

Poly38 P. trun

(4.2) 3.090 c 0.056 20.12 b 1.890

Poly38 S. zea

(10.6) 0.999 b 0.348 18.46 b 0.903

TH18 P. trun

(19.4) 1.045 b 0.173 2.27 a 0.780

TH18 S. zea

(25.6) 0.756 ab 0.181 0.46 a 0.047

Poly18 P. trun

(511.7) 2.785 c 0.100 19.42 b 1.746

Poly18 S. zea

(610.8) 2.819 c 0.076 0.72 a 0.423

THRT P. trun

(664.2) 0.23 a 0.091 16.94 b 0.839

THRT S. zea

(1105.0) 0.357 ab 0.127 15.95 b 1.011

PolyRT P. trun

(1420.3) 2.899 c 0.113 20.28 b 1.320

PolyRT S. zea

(2209.7) 3.232 c 0.034 28.15 c 3.167

a-c: In case where superscript in the same column do not share the same letter, they are significantly different (p>0.001). Multiple comparison with Bonferroni test.

TH38 P. trun= P. truncatus infested hermetic bag at 38oC; TH38 S. zea= S. zeamais infested hermetic bag at 38oC; Poly38 P. trun= P. truncatus infested polypropylene bag at 38oC; Poly38 S. zea= S. zeamais infested bag at 38oC; TH18 P. trun= P truncatus infested hermetic bag at 18oC; TH18 S. zea= S. zeamais infested hermetic bag at 18oC; Poly18 P. trun= P. truncatus infested polypropylene bag at 18oC; Poly18 S. zea= S. zeamais infested bag at 18oC; THRT P. trun= P. truncatus infested hermetic bag at room temperature; THRT S. zea= S. zeamais infested hermetic bag at room temperature; PolyRT P. trun= P. truncatus infested polypropylene bag at room temperature; PolyRT S. zea= S. zeamais infested bag at room temperature


64

Table 5: Linear correlation and regression analysis between the storage time (x) and weight loss or number of live insects (y) as influenced by various treatment combinations

Treatment % Weight loss Live insects (number) Combinations Correlation

coefficient (r) Regression equation

Correlation coefficient (r)

Regression equation

38 H Pt

-0.33 Y= 18.26 - 0.47x 0.84 Y= 1.64 - 0.34x

18 H Pt

0.71 Y= 13.27 + 1.05x 0.97 Y= 2.41 - 0.39x

Rt H Pt

0.66 Y= 1.55 + 1.09x 0.84 Y= 0.82 - 0.17x

38 H Sz

0.05 Y= 13.55 + 0.21x 0.85 Y= 1.23 - 0.25x

18 H Sz

0.74 Y= 0.56 + 0.03x 0.97 Y= 2.14 - 0.40x

Rt H Sz

0.12 Y= 15.28 + 0.19x 0.84 Y= 1.25 - 0.26x

38 P Pt

0.48 Y= 14.29 + 1.67x 0.62 Y= 3.37 - 0.08x

18 P Pt

0.84 Y= 8.30 +3.18x 0.94 Y= 2.01 + 0.20x

Rt P Pt

0.94 Y=7.05 +6.03x 0.77 Y= 2.17 + 0.21x

38 P Sz

0.27 Y= 17.43 + 0.29x 0.79 Y= 3.31 - 0.66x

18 P Sz

0.81 Y= -0.79 + 0.43x 0.91 Y= 2.36 + 0.13x

Rt P Sz 0.77 Y= 12.54 + 2.21x 0.96 Y= 3.05 + 0.08x

Regressing grain weight loss or number of live insects (Y) against storage time (X) showed

positive relationships with prediction equations in all the three temperature treatments but strong

correlations are recorded for weight loss mostly in the 18oC and room temperature conditions as

shown in Table 5.

*38H Pt= P. truncatus infested hermetic bag at 38oC; 38H Sz= S. zeamais infested hermetic bag at 38oC; 38P Pt= P. truncatus infested polypropylene bag at 38oC; 38P Sz= S. zeamais infested bag at 38oC; 18H Pt= P. truncatus infested hermetic bag at 18oC; 18H Sz= S. zeamais infested hermetic bag at 18oC; 18P Pt= P. truncatus infested polypropylene bag at 18oC; 18P Sz= S. zeamais infested bag at 18oC; RTH Pt= P. truncatus infested hermetic bag at room temperature; RTH Sz= S. zeamais infested hermetic bag at room temperature; RTP Pt= P. truncatus infested polypropylene bag at room temperature; RTP Sz= S. zeamais infested bag at room temperature


65

4.5 Oxygen depletion level There was an initial oxygen level 21% in each bag under the three different temperature

conditions. The triple layer hermetic under 38˚C recorded very fast oxygen depletion with time.

The oxygen reduced to as low 0.0% within 20 days in both P. truncatus and S. zeamais infested

maize. In the room temperature conditions, 0.0% was recorded in P. truncatus and S. zeamais

infested after 20 days under room temperature condition while it took up to 25 days for the same

to obtain such value under 18˚C temperature condition.

Figure 14: Oxygen depletion rate in hermetic bags under the three storage condition

*38 oC P. trun = P. truncatus infested hermetic bag at 38 oC; 18 oC P. trun = P. truncatus infested hermetic bag at 18 oC; RmT P. trun = P. truncatus infested hermetic bag at room temperature; 38 oC S. zea = S. zeamais infested hermetic bag at 38 oC; 18 oC S. zea = S. zeamais infested hermetic bag at 18 oC

0

5

10

15

20

25

1 5 9 13 17 21

O2

Dep

letio

n ra

te (%

)

Duration of storage (days)

38˚C P. trun18˚C P. trunRmT P. trun38˚C S. zea18˚C S. zeaRmT S. zea


66

4.6 Percentage germination viability

Germination viability test conducted in the field after storage inferred differences in the type of

insect species infesting the grain stored in two different storage bags and the conditions in

storage environment in terms of temperature. P. truncatus infested maize in polypropylene bag

under room temperature (27-32 ˚C) had the lowest germination percentage of 26.7%, the highest

germination percentage was recorded in hermetically stored maize under 18 ˚C temperature

condition and it was 90.0%. S. zeamais infested maize in polypropylene bag under room

temperature and 38 ˚C recorded 50.0% and 36.7% respectively while P. truncatus infested maize

in polypropylene bag under room temperature and 18˚C conditions recorded 30.0% and 33.3%

respectively. There was also high significant difference in the type of storage bags used with

hermetic bag recording the highest germination potential percentage.


67

Figure 15: Germination potential of maize stored under different conditions in two storage

bags

*lsd bar (p>0.05)

0

20

40

60

80

100

120

H38 Poly38S. zea

Ploy38P. trun

H18 Poly18S. zea

Ploy18P. trun

HRT PolyRTS. zea

PloyRTP. trun

% g

erm

inat

ion


% germdata


68

CHAPTER FIVE

5.0 DISCUSSIONS

5.1 Moisture Content

There were fluctuations in moisture content of the grain with duration of storage with regards to

the different temperature and type of storage bags.

It was observed at 38˚C temperature condition that there was a sharp increase in the moisture

content from the start of the storage to a mean of 18.0% in the hermetic bag after one month of

storage. The increment in moisture content continued gradually until after the third month where

it reduced and increased again in the fourth month where it remained relatively constant. This

trend could be attributed to high temperature, respiratory activities of the grain and the lack of

oxygen exchange between the bag and the store environment. The maize stored in the propylene

bag showed a gradual fall in the moisture content throughout the six months of storage probably

attributing to the high temperature and free flow of hot air in and out of the polypropylene bag.

The results obtained in the room temperature condition also showed fluctuations in moisture

contents in the hermetic bag. It increased sharply at two months after storage and remained fairly

constant with prolonged storage. This was possibly due to the rise (during the day) and fall (at

night) of temperature from December to February coupled with the respiratory activities of the

grain. There was little change (decrease) in the moisture content of the grains stored in

polypropylene bag. This agrees with Anankware et al., 2012, who reported a similar trend with

maize storage in low density polyethene hermetic storage.


69

In another case of 18˚C, moisture content in both hermetic and polypropylene reduced from the

initial 14.5% to 12.5% within the first month and remained fairly constant throughout the storage

period. This could be because of the constant low temperature which could not totally exclude

oxygen from the triple layer hermetic bag but hinders movement of moisture between the

environment and the storage medium as every condition remained fairly constant.

5.2 Number of Live Insects

In this study, there were few numbers of life insects in the triple layer hermetic bag than there

were in polypropylene in all the three temperature conditions. For instance, in the 38oC, no life

insect was found in the triple layer hermetic bags after the first month of storage for both S.

zeamais and P. truncatus. This was attributed to the drastic fall in O2 level in the triple layer

hermetic bags and the constant high temperature throughout the period of the study similar to

what was reported by Yakubu et al., (2011). Moreover, the insect and the grain itself respired

and used up the little O2 left in the bags which led to the suffocation of the insect. In

polypropylene bags, the study revealed less survival of S. zeamais in extreme temperature

condition. This is because no life insect was found in the bags at the end of the second month.

However, P. truncatus were found to have survived throughout the storage period with reduced

feeding and reproductive activities. This also confirmed the study carried out by Yakubu et al.,

(2011).

In the room temperature condition, the triple layer hermetic bags proved to be effective in

causing 100% mortality of the two insect species after the first month of storage due to low level

of O2 and respiratory activity of the insect and grain. These respiration activities could have

caused the build-up of CO2 and asphyxiation of the insect. Several hundreds of the insects were


70

found in the polypropylene bags in this setup at the end of the storage period. This could be

attributed to the fact that the polypropylene bag has an undisturbed exchange of air with the

environment which made the availability of O2 possible for the continuous growth and

development of the insect even though there was natural mortality.

In the other case of 18oC, the insects in the triple layer hermetic bags were found alive until the

end of the fifth month; however, the reproductive activities were reduced. In the propylene bags,

the insect numbers was not as high as the room temperature conditions. This confirms the results

of Yakubu et al., (2011) on maize stored in much lower temperature conditions. Generally, high

concentration of O2 (21.0%) in the propylene bag and the free flow of air between the stored

products environment and the surrounding atmosphere promoted the survival and/or continuous

reproduction of the insects. This was not true in the triple layer hermetic bags especially at 38oC

and room temperature conditions which suffered sharp depletion of O2 and made the condition

unfavourable for the insect to survive and reproduce (Navaro et al., 2002; Anankware et al.,

2012; Ansah et al., 2015). This study then made it safe to say that, the triple layer hermetic bags

prevents the growth and development of P. truncatus and S. zeamais while polypropylene does

not. More so, extreme temperature conditions retard the growth of the insect and makes survival

impossible.

In the course of the sampling of grains in the propylene bags at 38oC, 18oC and room

temperatures, other species of insects other than the introduced species were seen infesting the

grains. These include Ephestia cautella, Tribolium spp., Rhyzopertha dominica and other species

of Sitophilus. High moulds infestation was seen in the triple layer hermetic bags stored at 38oC

and room temperature which changed the colour and caused caking of the maize although there

was no statistical analysis carried out to satisfy this criterion.


71

5.3 Weight Loss

Weight loss of grains is brought about by the feeding activities of adult insects which include

eating out of the gem, scarification of the pericarp and consumption of the kernel leaving out

only the seed coat. In the case where the maize was stored at 38oC, there was no significant

difference between the weight loss recorded in the triple layer hermetic bags and the

polypropylene although there was a recorded weight loss in the polypropylene bags infested with

both insects species. This could be attributed to the fact that the temperature was too high and the

insect were not able to multiply in the polypropylene bag to cause a significant weight loss.

In the case of the 18oC treatment, the fact that there was no significant difference between S.

zeamais infested grains stored in the two different bags means that S. zeamais were not actively

feeding on the maize in the polypropylene bags during the storage period and this could be due

to the few numbers of life insects and constant low temperature in the stored product

environment which made the condition unfavourable for normal activities of growth and

development. However, P. truncatus were observed to have managed this condition and caused

significant weight loss of 19.42% in the polypropylene bag as compared to the 2.33% triple layer

hermetic bags.

In another case of room temperature treatment there was a significant difference between both

storage bags infested with P. truncatus (16.94% in triple layer hermetic bags while 28.15% in

polypropylene bags) and this confirms the results of the study carried out by Calderon and

Navaro, 1980; Murdock, 2003; Villers, 2006; Anankware et al., 2012; Ansah et al., 2015 who

reported little or no weight loss in hermetically stored maize. This result could be attributed to

the uncontrolled condition throughout the storage period which enabled the insect to multiply


72

and cause considerable weight loss as the condition was favorable for their normal growth and

development. Even though there were high numbers of S. zeamais recorded, no significant

difference was recorded in the weight loss between the two bags.

Greater weight loss was recorded in the polypropylene bags infested with P. truncatus than with

S. zeamais especially in the room temperature and this was expected as it has already been

established by many researchers that the insect cannot survive in extreme temperatures and

hermetic conditions (Anankware et al., 2012; Yakubu et al., (2011)). It has also been widely

reported that huge losses were recorded in polypropylene bags and other conventional storage

bags due to the fact that there is free and easy exchange of O2 between the bag and the

surrounding atmosphere. However, this was not true in this study in the temperature controlled

storage environment as the insects were not able to cause more damage in the polypropylene bag.

5.4 Germination Potential

From the results obtained, hermetically stored maize retained more viability of the seed than

polypropylene for all the three (3) temperature conditions.

The low germination potential in the polypropylene bags could be due to high level of insect

infestation which brought about damage of the germ plasm causing loss of seed viability. It was

also seen that P. truncatus infested grains performed poorly for all the three (3) treatments as

compared to S. zeamais infested maize and this is due to the fact that feeding activities of P.

truncatus causes more damage to the grains because they chew all the content of the maize

leaving only the seed coat. This confirms the study of De bruin (2006) and Anankware (2012)

who reported high viability of seeds of coffee and maize stored hermetically.


73

Considering the viability based on temperature conditions, the low viability recorded from maize

stored at 38oC could be attributed to the fact that high temperature conditions of more than 30oC

lowers the viability of maize as this could either increase or decrease moisture content of the

grains making it unfavourable to be used as seed.

Conditions of the maize in respect to moisture content was kept fairly constant and damage due

to insect was minimal in both the triple layer hermetic bag and polypropylene bag stored at 18oC

contributing to the high preserved viability.

5.5 Oxygen Depletion

Generally, the triple layer hermetic bags had a sharp decline of oxygen from the initial 21.0%

atmospheric oxygen in the bag at the beginning of the storage whereas this initial level remained

steady in the polypropylene bag for all the three (3) temperature conditions.

The lowest percentage oxygen was recorded in the triple layer hermetic bag stored at 38oC and

room temperature which recorded 0.0% oxygen within 20 days of storage. This was attributed to

type of polyethene (high density polythene) used for the work and this confirmed the findings of

Murdock et al., (2003) and Yakubu et al., (2011). Maize stored at 18oC temperature condition

could not achieve this level of oxygen in the hermetic bag, but was able to reduce the oxygen

concentration to 5.0%, this shows that cold temperatures does not warrant the total exclusion of

air from hermetic bags Yakubu et al., (2011).

The study therefore shows that total exemption of air could be achieved in high density

polythene bags in drier and higher temperature regions than could be in cold environment and/or

storage conditions.


74

5.6 Tensile Strength

High temperatures were seen to have increased the ductility and tensile strength of the polythene

as compared to the original state. This was because the longer the polythene was kept at 38oC,

the higher its tensile strength. Constant lower temperature however tend to decrease the ductility

hence, the tensile strength.

Room temperature condition proved to be making the polythene material brittle the longer it

stayed in that condition. This could be attributed to the fluctuations of the environmental factors

throughout the storage period. Consequently, uncontrolled heating and cooling of the

environment at different time of the day tend to have acted with the properties of the polythene

material affecting its stress and strain hence the tensile strength.


75

CHAPTER SIX

6.0 CONCLUSION AND RECOMMENDATION

6.1 Conclusion

The study entails the effect of temperature on the effectiveness of the triple layer hermetic

storage bag in controlling the S. zeamais and P. truncatus against maize. The tensile strength of

the bag as affected by temperature, oxygen depletion level in the hermetic bag as well as the

viability of the maize after storage at different temperatures was also studied alongside.

In conclusion;

1. The triple layer hermetic bag can be said to have effective control against P. truncatus

and S. zeamais on maize stored at different temperature conditions.

2. Storage of products in the triple layer hermetic bag at constant high temperatures

increases the ductility of the material which could prolong its usage. On the other hand,

where temperature and/ or other environmental factors are not kept constant and the

daytime temperature was way higher than the temperatures at night, the ductility of the

material decreases and hence brittleness of the polythene material which makes its

prolonged use for storage unfavourable.

3. Maize stored hermetically at high temperature conditions tends to gain moisture rapidly

thereby enhancing the development of moulds which bring about caking, colour changes

and spoilage of the maize. It is safe to conclude that use of triple layer hermetic bags at

lower temperature conditions has advantages over the higher temperature zones, as

minimal gain in moisture was experienced in the lower temperatures and no damage

caused by moulds. The maize stored at lower temperatures looked attractive after six


76

months of storage while the change in colour caused by the moulds at high temperatures

made the maize unattractive and this may decrease its market value.

4. Seed viability is preserved in the triple layer hermetic bag although it is negatively

affected by high temperatures.

5. High density polyethylene could totally deplete oxygen but this could not be achieved at

temperatures less than 20oC. The least oxygen concentration obtained at 18oC was 5.0%

after 23 days of storage. However this was able to inhibit the development and

reproduction of the insects.

From these findings, it can be deduced that triple layer hermetic bag is very effective in

controlling P. truncatus and S. zeamais in different temperature conditions although it may not

be suitable for prolonged storage at high temperature especially where high density polyethylene

is to be used.

The use of the triple layer hermetic bags to store maize will hopefully grow widely with proper

agricultural extension programs to create awareness for the farmers and encourage them to

experience the advantages of using it over chemicals. Use of hermetic bags to store maize should

be incorporated with other non-chemical method of controlling insect as integrated method of

insect control so that good quality maize could be available for consumption and planting and

there would be no danger or fear of unacceptable level of chemical residue in grains.


77

6.2 Recommendation

Knowledge gaps need to be closed in further studies to help farmers in different climatic

conditions to make wise decision as to what type of hermetic bag is suitable for them in terms of

density of the polyethene. High density polyethene bags should be preferred in low temperature

(≤ 25 ˚C) zones to keep the development of mould in check.


78

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APPENDICES

APPENDIX I

Maize stored hermetically at 380 C after six (6) months

APPENDIX II

Maize stored hermetically at room temperature after six (6) months


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APPENDIX III

Maize stored hermetically at 180 C after six (6) months

APPENDIX IV

Student sieving maize for sampling at entomology laboratory


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APPENDIX V

Pieces of polyethylene materials used ready for tensile strength analysis

APPENDIX VI

Analysis of variance Variate: NUMBERS Source of variation d.f. s.s. m.s. v.r. F pr. REPS stratum 2 0.0323 0.0161 0.04 REPS.*Units* stratum TREATMENTS 11 313.5639 28.5058 66.21 <.001 Residual 202 86.9649 0.4305 Total 215 400.5611


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Analysis of variance

Variate: Moisture Content Source of variation d.f. s.s. m.s. v.r. F pr. REP stratum 2 1.0156 0.5078 0.58 REP.*Units* stratum TEMP_C 5 629.3322 125.8664 142.79 <.001 Residual 100 88.1489 0.8815 Total 107 718.4967

Analysis of variance

Variate: %WL Source of variation d.f. s.s. m.s. v.r. F pr. REP stratum 2 28.50 14.25 0.37 REP.*Units* stratum TEMP_C 11 15096.78 1372.43 35.29 <.001 Residual 202 7856.79 38.90 Total 215 22982.06


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