Proceedings of the 7th Iniernatumol Workmg Conference on Stored-product Protection - Volume 2

Surveys for fungal pathogens of storage pests infesting maizein Kenya; first records of Beauveria spp

George Oduor", Sue Srmth", Ephraim Chandi", Lucy Karanja", John Agano' and Dave Moor~

Abstract

Sitophuus zeanuus , Proetephanus trumcatus , Sitotrcqacerealella and Triboltum spp. are among the major pests ofstored maize m Kenya, the control of which currently reliesmamlyon the use of morgamc pesticides In an attempt toseek an alternative control strategy, a survey for fungalpathogens mfectmg these pests was conducted m the LowerMIdland, Upper MIdland and Lower HIghland agroecologicalzones m Kenya. Samples of infested maize collected from125 farms showed that S. zeanuus constituted more than75% of the msects found The entomopathogemc fungusBeauierui spp was recovered from 12 of the 125 farms,and mamly from S zeanuns .

Introduction

Maize constitutes an Important source of carbohydrates to alarge part of the Kenyan population Most of the maize mKenya ISgrown m the provmces of RIft Valley, Western andNyanza, especially in the Lower HIghland (LH), UpperMIdland (UM), Lower MIdland (LM) and Lowland (L)agroecological zones. After being harvested maize ISusuallystored m different forms Ccobzhusked, coh/dehusked,shelled etc. ) and structures (loft, outside or mside stores,etc) as It awaits consumption Although mfestation ofmaize by dIfferent arthropod pests ISImtiated m the fIeld, Itis m the store where economIC damage becomes moreapparent. BeSIdesthe recently mtroduced larger gram borer(Prostephanus truncatus), other pests whIch mfest storedmaize mclude the maIze weeVIl (SLtophilus zeamaLS),angoumOlsgram moth (Sitotroga cerealella) and the flourbeetle (Triboll um spp) MaIze gram losses due to thesepests have been estimated to be over 30% (DeLIma, 1978;Nyambo, 1993). Attempts to mmImise these losses havemcluded tradItional methods by use of wood ash and herbsamong some small-scale farmers, and conventional methods

1 CAB International, Afnca Regional Centre, POBox 633 VillageMarket, Nairobi, Kenya

CAB International BIOSCienceUK Centre, Silwood Park, BuckhurstRd , Ascot, Berks SL5 7TA, UK

by use of inorganic pesticidesThe efficacies of wood ash and herbs at controlling pests

of stored maize have not been quantified and therr use ISrestncted to small stores Inorganic pesticides may be tooexpensive for most farmers and their use may lead todevelopment of resistance and may also have detnmentaleffects on non-target organisms (mcludmg man). Smcesmall-scale farmers produce most of the maize m Kenya, itISImperative to develop pest control strategies that are bothenvironmentally safe and economically feasible. The use ofthoroughly studied and selected entomopathogernc fungi maybe such a strategy. Unlike other pathogens used m biologicalcontrol, fungi are unique m bemg able to penetrate throughthe arthropod cuticle, and therefore do not have to beconsumed to cause infection Many studies evaluatmg thepotential of fungi as biologtcal control agents have beenconducted, and some fungi are registered microbial controlagents Rodrigues and Pratissoh (1990) demonstrated thatmaize treated With the entomopathogen Beauoeria bassuinawas protected from mfestation by the weevil S. zeamuusfor a penod of 6 months Fungi may also be used IIIcombination WIth other btopesticides to synergise the effectof each pathogen against stored pests Sandner et al. (1972)showed that mortality of S oranarius treated with allmixture of B bassuuui and Bacilius thuringiensis(Thuncide ) was 83% as compared to 65%, the maximumattamed when either pathogen was used mdrvidually.A natlOn-WIdesurvey for mdlgenous pathogens mfectmg

various pests of stored maIze was therefore undertaken mKenya. The long-term aim was to search for a blOlogicalcontrol strategy that could supplement the current controlpractices

Materials and Methods

In the survey, an attempt was made to cover the entiremaize growmg zones m Kenya. However, areas wherefarmers had little or no stored maIze, due to a preVIOUSsevere dry spell, were not VISIted Farms were selectedWIth the aSSIstance of staff from dIfferent local DlstnctAgnculturalOffices.In each dlstnct, samples were taken from dIfferent

agroecologlcal zones (AEZ's ) m WhIChstored maize wasfound For unshelled maIze, 5 to 6 heaVIly mfested cobs

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Proceedings of the 7 th Internaiumal Workt'ng Conference on Stored-product Proiectum - Volume 2

were selected from each farm and put in 10cm diameter x20cm high glass jars with tight fitting perforated hdsShelled maize (about 2 kg) was shaken through two 20cmdiameter SIeves, one placed on top of the other. The uppersieve (3 mrrr' mesh size) retained the maize grams butallowed the insects and maize dust to pass through andcollect on the lower sieve (1 mrrr' mesh SIZe). The lowersieve allowed the dust to pass through, and the retamedinsects were then brushed into a glass Jar similar to thatdescnbed above. Some maize grains were added to the jar toserve as food to the msects. A total of 125 farms in 12districts were sampled.The collected insects were thereafter sorted by species in

the laboratory, into dead and hve mdrviduals, To check ifsome of the live individuals were infected, they were rearedon crushed maize grains and mortality was monitored everyother week for a penod of 4 weeks. To determine whetherdeath was due to fungal myCOSIS,all the dead insects, (thosecollected dead and those which died after collection) weresurface stenlised by dipping them in 5.00 % sodiumhypochlorite for 2 mmutes, rinsed m sterile distilled waterand placed on moist filter paper at the bottoms of 9 emdiameter Petn dishes With firmly fitting hds. The disheswere then placed in an incubator (27°C) and observed everyother day (for 10 days) for fungal infection. Fungi wasisolated from infected cadavers by moculation of conidia( aerial spores) onto Sabouraud Dextrose Agar (SDA)medium With 1.1 % antibionc (Penicilhn andStreptomycin) .

Results

S. zeamais was, by far, the most common pest speciesfollowed by Tribouum. spp. Others included P. truncatus,Carpophilus sp., Oryzaephilus sunnamenstS, Rhizaperthadaminica and Oryptolestes fernunneus, Although commonlyseen flying about, Sitotrqp cerealeUa moths were not counteddue to their high mobility. The species composition m the 3agroeoological zones is shown in Table 1. S. zemuusconstituted between 75.5 % (in 1M) and 80.5 % (m Lll) ofthe insects found S. zeamais was also observed in the highestdensity, attainIng an average of 727.8 per farm in Uf. Anaverage of aoout 40% of the individuals were dead by the timethe samples were sorted. Tribolium spp. was the second mostcommon pest, and, like S. zeamais, was most abundant in Ufand least in 1M AEZ's. However, the populatlon of Triboliumsp. was between 7.7 and 12.6 % that of S. zeamatS. P.truncatus was found only in UM and 1M AEZ's and m only onedistrict, Taita 'Thveta.The entomopathogen .Beauveria sp. was Isolated from

insects collected from 12 of the 125 farms sampled (Table2) . A total of 89.7 % of the mfected insects were S.zeamatS, although Tribolium and Carpophilus spp. also

yielded this fungus. The fungus was very WIde spread,occurring m all the AEZ's and in 9 of the 12 districts visited.Although .Beauveria was recorded over a Wide area theproportion of insects from which it was Isolated m each farmwas very small, ranging from 0 .08 to 0.94 %. A total of 23of the 29 insects from which the fungus was Isolated weredead when collected.

Discussions

The status of S. zeamuus as the most common pest ofstored maize m Kenya was shown. The numericalsupenorityof S. zeamais was not uniform even within thesame AEZ. In the Lower MIdland, for example, Itconstituted an average of 75.5 % of the collected msects,yet similar estimates Within the same AEZ were 99.9% mMigori distnct and 14.7% m Taita region of Tarta Tavetadistrict, The overall dommation of S zearna,tS may bebecause It IS a primary pest, which has been in Kenya for avery long time. P. truncatus on the other hand, ISrelatively new m Kenya having entered from Tanzania in1983 (Kega and Warm, 1983). This explains Its dominancein Taveta region, which borders Tanzania. FIeld trials toquantify maize grain losses due to P. truncatus have notbeen conducted in Kenya but are bound to show enormouslosses. Increased movement of maize, especially after cropfailure m some parts of Kenya, is hkely to hasten the rate atwhich P. truncatus will spread inland from Taita Tavetadistrict. Although pheromone traps placed in different partsof Kenya indicate that P. truncatus has reached the mainmaize producing zone in the Rift valley (personalcommunication, G. Farrell), this survey detected the pestin the stores only m Taita Taveta districtThe environment m a maize storage structure has been

considered to be too dry to support the growth of fungi.However, this survey recovered B. bassiana from stores in12 locations in 9 different distncts ThIS IS the first time B.bassuma has been Isolated from insects mfestmg storedmaize m Kenya . .Beauveria sp. was isolated not only fromS. zeamais but also from Triboltum and Carpophilusspp . This shows that proper formulation and apphcation ofthis fungus may Infect a WIde range of maize storage pests.The Beauwria sp. collected from the 12 locatlons will be

characterised to see If they are distlnct isolates. From these onlyone or a few will be selected for further development. Selectlonwill be 00sed on tests mcluding pathogeniCIty (the pathogenicityof some isolates to S. zeamais and P. truncatus has beendetermmed), SpecIfIcity (to assess the host range and possibleeffects on non- target orgamsms) and environmental tolerance(to determine persIstence under conditions m typIcal maizestores) . Stumes on improved formulation and applIcationtechniques for the selected isolates to maximise dose transfer totarget insects are being carried out.

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Proceedings of the 7th International Working Conference on Stored-product Protection - Yolume 2

Table 2. locations where Beancoerui spp, was found mfectmg pests of stored maize and the proportion of insects mfected bythis fungus.

DIstrict AEZInsects collected Number msects Proportion of

at farm mfected mfected msects (%)

Nyarrnra LH1 639 5 (S~tophilus)

1 (Triboliurn) 0.94

Nakuru LH2 707 1 (Sitoph~lus) 0.14

Uasm Gishu LH3 825 2 (Sitoph~lus) 0.24

Uasm Gishu LID 1392 7 (Sitoph~lus) 0.50

Uasm Gishu LID 1154 1 (Sitophilus) 0.09

Uasin Gishu LID 565 1 (S~tophilus) 0.18

TaIta Taveta UM1 1271 3 (S~tophilus) 0.24

Gucha UM1 690 1 (Sitophilus) 0.14

Trans NZOla UM3 1288 1 (Sitophilus) 0.08

Siaya LM3 753 1 (Triboliurn) 0.13

Kuria UM3-4 774 3 (Sitophilus) 0.39

Kisii LMI 38 1( Sitophilus )

1 (Carpophilus) 0.27

Acknowledgement References

This publication IS an output from a research project fundedby the Department for International Development of theUnited Kingdom. However, the Department forInternational Development can accept no responsibility forany mformation provided or VIews expressed. DFID projectR6509 Crop Post Harvest Research Programme

Del.una, C P F 1978. A study of the bionomics and controlof Suophiius zearnais Motchulsky and Sitotrogacerealella (Ohver ) and associated fauna in stored maize,under laboratory and field condrtions in Kenya. PhDTheSIS, University of London.Kega, V. K and Warui, C. W. 1983 Prostephanustruncatus in Coast Province, Kenya. Tropical Stored

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Proceedinqs of the 7th Iniernatioruil. Worhng Conference an Stored-product Protectwn - Volume 2

product Information, 46, 83Nyambo, B. T 1993. Post harvest maize and sorghum gramlosses in tradrtional and improved stores in South NyanzaDistrict, Kenya International Journal of Pestmanagement, 39, 181-187.Rodngues, C. and Pranssoh , D 1990. Patogerncidade deBeauoerui brtnupuarts: (Sacc) Petch e Metarluzium

oausopluie (Mots.) Sok e seu efeito sabre 0 gorgulho derrulho e caruncho de feijao Anais da SociedadeEntomologica do Brasil, 19, 302 - 306Sandner, H., Szczypiorska, M and Wegorek, W. 1972An integrated use of pathogens of msects and insecticidesin plant protection. Plant Protection Institute Bulletm,52, 45 - 54

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