INFLUENCE OF TEMPERATURE AND HOST ON THE...

Influence of temperature and host on the rateof population increase of the egg parasite,

Trichogramma sp. (Hymenoptera: Trichogrammatidae)

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Authors Martinez, Andrew Orlando, 1944-

Publisher The University of Arizona.

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INFLUENCE OF TEMPERATURE AND HOST ON THE RATE OF POPULATION INCREASE OF THE EGG'PARASITE, TRICHOGRAMMA SP.

(HYMENOPTERA: TRICHOGRAMMATIDAE)

byAndrew 0. Martinez

A Thesis Submitted to the Faculty of the■ DEPARTMENT OF ENTOMOLOGY

In Partial Fulfillment of the Requirements For the Degree of

' MASTER OF SCIENCEIn the Graduate College

THE UNIVERSITY OF ARIZONA

1 9 7 0

STATEMENT BY AUTHOR

This thesis has been submitted, in partial fulfillment of the requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.

SIGNED : {D,

APPROVAL BY THESIS DIRECTOR This thesis has been approved on the date shown below:

T. F. WATSON , 7 Dfte /Professor of Entomology

/x _ /f/,

ACKNOWLEDGMENTS

To my wife, Yolanda, whose encouragement and patience made this possible, I dedicate this thesis with my most sincere gratitude.

. The author also wishes to .express his sincere appreciation to Dr. Theo P. Watson, who served as his major advisor and whose guidance, encouragement, and invaluable assistance are. gratefully acknowledged.

I also extend my appreciation to Drs. George W. Ware and Robert Fye, who served on my graduate committee and assisted in reviewing of the manuscript,

Special thanks are expressed to Messrs. Paul Johnson and Edward Rivera for their technical assistance in the laboratory.

TABLE OF CONTENTSPage

LIST OF TABLES . . . . . . . . . . . . . .......... . vLIST OF ILLUSTRATIONS. ■ . . . . . . . . . . . . . . . . viABSTRACT....................... . viiINTRODUCTION . . . . . . . . . . . . . . . . . . . . . 1METHODS AND'MATERIALS . . . . . . . . . . . . . . . . . 3

■ Description of Incubation Chambers...... 3Establishment and Maintenance of TrichogrammaCulture . . . . . . . . . . . . . . 4Establishment and Maintenance of Host Cultures. 4

Pectinophora gossyplella. . . . . . . . 4Trichoplusla ni . . . . . . . . . . . . 5

Developmental-Period Studies. . . . . ........ 6Fecundity and Longevity Studies . . ........ 7Statistical Methods . . . . ................... 7

RESULTS AND DISCUSSION ............... 11Host-Egg Influence on the Biology, and PopulationGrowth of Trichogramma s p ............ 11

Developmental Period. .......... 12Adult Longevity . . . . . . . . . . . . 12Parasitization and Fecundity. ........ 14Population Growth ............. . . . . 23

■ Temperature Influence on the Biology and Population Growth of Trichogramma sp.......... 24

Effects on Developmental Period . . . . 24Effects on Survival Rate and AdultLongevity ........ . . . . . ........ 24

Effects on Fecundity. . . . . . . . . . . . . . 25Effects on Population Increase. , .......... 27

SUMMARY. .............. 32APPENDIX: LIFE-FECUNDITY TABLES . . . ........ . . . . 34LITERATURE CITED . .......... ' . . - 4l

iv

LIST OF TABLES»

Table ... Page1. Developmental period of Trlchograrnma sp,

in the eggs of Pectinophora gossypiella and Trlchoplusla nl at various "constant temperatures 13

2. Parasitization, fecundity and longevity ofTrlchograrnma sp. on the eggs of Pectinophora gossypiella "and Trlchoplusla ni at various constant temperatures ....................... 15

3. Comparative population parameters of Tricho- gramrna sp. on the eggs of Pectinophora gossypiella and Trlchoplusla ni at various constant temperatures . . ................. 29

v

LIST OF ILLUSTRATIONS

Figure Page1. Survival and age-specific parasitization

curves for Trichogranana sp. on the eggs' of Pectinophora gossypiella and Trichoplusla niat 68OF. . . . . . . . . . T . . . . . . . . 17

2. Survival and age-specific parasitization curves for Trlchograrnma sp. on.the eggs of Pectinophora gossypiella and Trichoplusla niat~75°F7 . . : '. . . . . . . . "Tl . . ~.“T . . 18

3« ' Survival and age-specific parasitization curves for Trichogramma sp. on the eggs of Pectinophora gossypiella* and Trichoplusla ni at 83°F7"' . . . . 19

4. Survival and age-specific fecundity curves for Trichogramma sp. on the eggs of Pectinophora gossypiella and Trichoplusla ni at '68~Dfh • • • • 20

5. . Survival and age-specific fecundity curves forTrichogramma sp. on the eggs of Pectinophora •gossypiella and Trichoplusla ni at 75°F, • • • • 21

6. Survival and age-specific fecundity curves for. Trichogramma sp. on the eggs of Pectinophora gossypiella and Trichoplusla ni at 83^FT . . . . 22

vi

ABSTRACT

The biology and population Increase of the hymenop- terous parasite Trichograrnma sp. developing in the eggs of the pink bollworm, Pectinophora gossypiella (Saunders) and the cabbage looper, Trichoplusia ni (Hubner) under various constant temperatures, were studied in the laboratory.

The intrinsic rate of increase (rm ), net reproduction rate.(Ro), mean generation time (T) and finite rate of increase (X ) were the basic parameters utilized in assessing temperature and host-egg influence on the biology and population growth of the parasite.

The population of the parasite increased more rapidly in the eggs of T. ni than'in the eggs P. gossypiella at all temperatures. The developmental period, total fecundity and age-specific fecundity were also affected by the host egg.

Temperature influenced population growth by affecting adult longevity and fecundity. Considerable differences in the intrinsic rates of increase among the various constant temperatures occurred. The maximum increase occurred at 83°F. in both host eggs..

vii

•INTRODUCTION

Members of the genus Trichogramma (Hymenoptera: .Trichogrammatidae) are important parasites of many lepidopterous species. The tiny wasp, by means of. its ovipositor perforates the chorion of the host egg and deposits its own

• egg inside. The parasite larva feeds on the content of the host until ready to emerge as an adult. The Trichogramma used in these studies was a recently discovered uniparental species, known as the Peruvian strain.

During recent years entomologists have expended considerable time and ingenuity in an effort to utilize successfully this egg parasite. Although Trichogramma have been widely used as potential biological controls of many insect pests, very little is known about the effects of.the host egg and temperature on the biology and population growth.

Host egg and temperature influences on the biology of Trichogramma have been reported'by Salt (1941) and Lund (1938), respectively. Since population increase is dependent on numerous environmental factors, the host egg and temperature being among the most important, in these.studies the effects • of these two factors upon the capacity of the parasite to increase in numbers were the primary concern. Effects on the biology of the Trichogramma were also investigated.

' 1

Life-fecundity tables were constructed for the parasites reared in the two different hosts under various constant temperatures. Utilizing the data in these tables, the intrinsic rates of increase were calculated. This parameter was used in evaluating the effects of the host and temperature on population increase.

METHODS AND MATERIALS

Description of Incubation Chambers Temperatures in these studies were selected to corre

spond as nearly as possible with the average ambient temperatures occurring in the natural environment during the period of expected Trichogramma activity.

Five modified household refrigerators, 11 ft.3, were used as incubation chambers and were programmed to operate at 58s, 68°, 75°, 83°, and 95°F. The heating and cooling cycle in each chamber was controlled by two Fenwall thermoswitches adjusted two degrees above and below' the programmed temperature. Heat for each chamber was supplied by a 75-watt ni- chrome wire coil (Eagle Cone Glocoil) and the cooling was supplied by the intact refrigeration unit. A Calrad ventilation unit (Model A.C.M.) turning a 2.5 inch fan circulated the air in each cabinet. The relative humidity was maintained, between 40 and 70 > in each chamber by a Honeywell humidity control which regulated the operation of a small fan above a shallow pan of water. Continuous light for 12 hours daily was provided by two 15-watt cool-white fluorescent lamps. r . . The temperature in each chamber was monitored twice

daily by the use of a temperature potentiometer (Leeds and

4Northup Co., cat* no. 8692) connected to thermocouples in each chamber.'

Establishment and Maintenance of Trichogramma. Culture

The Trichogramma u?ed in these studies were the progeny which resulted' from parasitized Sitrotroga eggs obtained from the University of California,' Riverside. .The original culture was collected from parasitized lepidopterous eggs on cotton in Peru. The parasite had not been definitely identified at the time these studies were completed. Although there was strong evidence that it may belong to the T. semi- fumatum or T . pretiosum complex.

Two separate cultures were maintained in the laboratory throughout the study. One was maintained on eggs of P. gossypielia and the other on eggs of T. ni. Both stock cultures were maintained at 75°F.

A microaspirator and a small brush were used to manipulate the parasites. One-pint mason jars served as rearing containers.

A 10^ sucrose solution streaked on the sides of the jars served as the food source for the adult. Trichogramma.

Establishment and Maintenance of Host CulturesPectinophora gossypielia. Adult pink bollworm moths

were collected daily, April through June, from field emergence

cages placed over Infested cotton debris and located at the University of Arizona Experimental Farm, Tucson.

The moths were taken to the laboratory and placed in round half-gallon ice cream cartons (100 moths per cage) which served as oviposition cages.

A three-dram vial containing a 10$. sucrose solution, . stoppered with a cotton wick, and inserted through an opening on the lid of the oviposition cage, served as the food source for the adult moths.

Eggs were collected on strips, of paper towel placed over a 4-inch square opening cut on the lid of each oviposl- • tion cage. A square piece of screen (l6 meshes per inch), was glued over the opening. The strips of paper towel were held firmly against the screen by a weight.

The eggs were incubated at 83°F. until, hatch occurred. The larvae were then transferred into 1 oz. plastic cups containing -g oz. of lima bean medium (Shorey 1963) and incubated at 75°P. until adults emerged.

Trichoplusia ni. Adult cabbage looper moths were obtained from a small culture already established in the laboratory.. The adults were maintained in one-gallon glass jars (25 moths per jar). A 10$ sucrose solution was provided the adults as described above.

Eggs were collected on strips of paper towel placed on the sides and lid of the rearing containers. The eggs

were washed with a sodium hypochlorite solution and rinsed with a sodium thiosulfate solution as a precaution against the cabbage looper polyhedrosis vihus.

The eggs were incubated'at room temperature (oiJ2°F.) until hatch occurred. The larvae were reared in one-pint, wax-treated ice cream cartons on lima bean medium (Shorey 1963) and incubated at room temperature until adults emerged.

Developmental-Period StudiesHost eggs not more than 24 hours old were exposed to

50 adult Trichogramma in a one-pint mason jar for a period of one hour at 75°F• At the termination of the exposure period the host eggs were removed, divided into five groups and incubated at the five constant temperatures.

When the eggs showed signs of parasitization, they were transferred singly into one-dram shell vials and incubated at the respective temperatures until emergence occurred, The open end of the vials Was sealed with a cotton plug. .

The time of parasite development was measured from the termination of the egg exposure period to emerge of adults and recorded in days. Records of the number of progeny that emerged per parasitized egg were also kept.

7Fecundity and Longevity Studies

Host eggs were collected dally, counted and exposed to single newly-emerged and fed Trlchogramma In a 3i>" x petrl-dish at the desired temperature. The eggs were exposed to the Individual for a period of 24 hours. At the termination of the exposure period the parasite was removed, placed in another petrl-dish containing fresh host eggs, and returned to its incubator. This same procedure was repeated until the parasite died.

:The exposed host eggs were incubated until emergence occurred. Longevity, parasitization, and progeny records were kept for each individual.

... Statistical MethodsLife-fecundity tables as described by Andrewartha and

Birch (1954), were used to evaluate most of the data obtained in these studies. The intrinsic rate of increase (rm ), net reproduction rate (R0), mean generation time (T), and finite rate of increase (X) were calculated for each groupof parasites at the various temperatures. . These tables are presented in the Appendix and are summarized in tabular and graphical form in the text. Since immature mortality was negligible, the calculations for the first day of adult Ilfe were based on an adult population equal to the immature population (lx = 1.00).

Birch (1948) describes a method for calculating theintrinsic rate of natural increase (rm ). He defines it as the constant ’rm1 in the differential equation for population growth under specified environmental conditions in which food and space are unlimited:

This growth rate (rm ) can also be expressed in the integrated form:

N0 = number of individuals at time zero,Nt = number of individuals at time t, rm = infinitisimal rate of increase, e = base of Naperian logarithms.

The calculation of rm is based on the female population and is computed from the data contained in the life- fecundity tables (see appendix). The rm can also be approximated by the following equation

wherelx = survival rate at age x, mx = age-specific fecundity rate.

Mathematical tables for powers of e are readily available, therefore, the equation is most easily solved by multiplying

dN/dt = rN.

Nt = N0ermtwhere

9both sides by e?. The method is described by Birch (1948) and, more recently, in detail by Watson (1964).Then:

e7 2, e - V lxmx _ e7

e7"rrnXlxmx - 1096.6 (1097).Two trial rm 1s were calculated for each temperature

by utilizing the above equation and the data in the life- fecundity tables. One rm made the left side of the equation slightly less than 1097 and the other rrn made it slightly more than 1097. In order to better estimate the true rm it was found necessary to compute it, through graphical interpolation, to three decimal places by plotting the provisional rm ’s against their sums. The method is described in detail by Watson (Figure 4, 1964). Under this method, the probability at emergence of being alive at age x was designated lx and the mean number of progeny produced in unit time by an individual of age x was designated mx .

The other parameters necessary in determining population increase were also computed from the data presented in the life-fecundity tables. The net reproduction rate (R0 ) is the rate of multiplication in one generation and was obtained by the summation of the lxmx column in the tables.Thus:

K0 “ 2 ^xmx*

The mean generation time (T) was calculated, by using the following formula:

T = log e R0 .

In some circumstances it is more useful to calculate the finite rate of increase (A )* which represents the number of times a population multiplies in unit time in an unlimited environment. The finite rate of increase is the natural antilogarithm of the intrinsic rate of increase (rm ):

A. = antilog e rm .

The mean (X) and standard deviation from the mean (SD) were used in analyzing and summarizing data not included in the life-fecundity tables.

RESULTS AND DISCUSSION

Host Egg influence on the Biology and Population Growth of Trichogramma ‘sp. ~

The two host-egg types utilized in these studies represented two different genera of the Order Lepidoptera and varied extensively in size and shape. The eggs of T . ni were spherical in form and averaged 0.5 mm. in diameter.While the eggs of P_. gossypiella ■ were somewhat ovoid in shape and averaged 0 .58 mm. in length and 0.34 mm. in diameter.

Quednau (i960) reported that the ideal Trichogramma host has a chorion which is not more than 5>(in thickness and has a diameter of 0.5 mm. This type of egg is best represented in the family Noctuiidae■

Salt (1941),. based on studies with T. evanescens,., reported that the host egg' imparted a definite effect on the biology of the developing parasite. He found that the host egg affected the size, form, developmental period, physiology, - and behaviour of the Trichogramma. He also found evidence of host-egg influence on parasite fecundity, longevity, and vigor. •

In the present study the host egg proved to be an .important factor affecting not only the biology of the parasites but also their innate capacity to increase in numbers.

11 . ' .

" : ■ 1 2

Developmental Period To determine the Influence of the host egg on the

developmental period of Ti sp., parasitized host eggs were Incubated under similar conditions at the various constant temperatures. The results' are presented in Table 1.

The results indicate that certain variations in the developmental period of Trichogramma sp. reared in the two different hosts, occurred. These variations afe perhaps to- be attributed to the differences in the host eggs, i.e., size, shape, chemical composition, etc. In every instance individuals developing in the eggs of T. ni emerged sooner than individuals reared under similar conditions in the eggs of P_. gossypiella. The differences were more profound at the higher temperatures. At 75°F•^'where parasite emergence was carefully observed on both host eggs, it was noted that when two or more individuals shared one T. ni egg, they emerged earlier than solitary parasites.

Although these observations do not permit a definite conclusion, they do suggest that the host egg influenced the speed of development of the parasite. The differences shown in Table 1 are not statistically significant.

Adult Longevity '. Adult longevity was studied in conjunction with para-

sitization and fecundity studies. The results are presented

J

TABLE 1DEVELOPMENTAL PERIOD OF TRICHOGRAMMA SP. IN THE EGGS OF PECTINOPHORA GOSSYPIELLA

AND TRICHOPLUSIA NT AT VARIOUS CONSTANT TEMPERATURES

HOST EGG

Temp.F

P. gossypiella T. niNo. of Tests

Range • (Days)

X Developmental- Period (Days)

1/ No. of Tests

Range X (Days)

Developmental- Period (Days)

59 184 24.5-27.5 25.812.2 192 23.0-26.3 24.6i3,468 183. •' 14.0-15.5 14.911.1 184 14.0-15.0 l4.6il.l75 183 9.0-11.5 11.410.9 191 9.3-IO.5 9.710.983 183 9.0- 9.5 . 9.110.5 187 7.5- 8.3 . 7 .810.9

- 95 200 -- 200 — — — — — —

1/ Differences in development due to host egg are not statistically significant.

14in Table 2 and are based on 30 individuals at each temperature.

Adult longevity within temperatures was essentially the same, regardless of the host egg. For example,^at 75°F. adults reared in P. gossyplella eggs lived an average of 5.2 (i 1.9) days, compared with 5.1 (i 2.2) days for individuals reared in T. ni eggs. Similar results were obtained at the other temperatures.

Survival curves presented in Figures 4-6, also fail to reflect any significant differences in longevity attributable to the host. An immature period of development precedes each curve.

Parasitlzation and FecundityThe results- of the parasitization and fecundity

studies are shown in Table 2 and are also based on 30 parasites per temperature.

These results indicate that, regardless of the incubation temperature, the host egg demonstrated a profound influence on parasite activity and prolificacy. The eggs of T. ni_ yielded more progeny at all temperatures, but more P. gossyplella eggs were parasitized in all cases. This irregularity was primarily due to the fact that the parasite had the capacity to limit egg.deposition to one egg per P. gossyplella egg regardless of the temperature, while in the

TABLE 2PARASITIZATION, FECUNDITY AND LONGEVITY OF TRICHOGRAMMA SP. ON THE EGGS. OF PECTINOPHORA GOSSYPIELLA AND TRICHOPLUSIA NI AT VARIOUS CONSTANT TEMPERATURES (30 PARASITES PER TEMP.)

Temp.Op

HOST EGGP. gossypiella T. ni •

No. Eggs Exposed

Para- 1/ sitization

Pro- -2/ ductivity

Lon- 3/ No. Eggs gevity Exposed

Para- 1/ sitization

Pro- 2/ ductivity

Lon- 3/ gevity

68 26,875 48.5+15.9 45.3+14.7 5.7±1.6 11,126 31.1+11.5 72.3+27.8 5.7+2.175 31,492 56.6±l8.6 52.6+17.4 5.2+1.9 8,599 37.2+12.4 87.3+31.0 5.1+2.283 20,449 47 , 24:20. 2 43.8119.5 3.4+1.1 6,091 27.4+11.2 54.3+24.4- 3.3+1.195 ; 6,300 0 0 0.2+0.1 2,039 0 0 0 .2+1.1

1/ Differences in parasitization are not statistically significant. 2/ Differences' in fecundity are not statistically significant.3/ Differences in longevity are not statistically significant.

HVI

16eggs pf T. nl multiple depositions during one act of ovi- posltion were not uncommon. At 73° ^ which proved to be optimum for both parasltization apd productivity on both host eggs, the mean number of progeny obtained per T. ni egg was 2.5 compared to 1.0 per P. gossypiella egg. Similar results were obtained at the other temperatures.

Quednau (i960) suggested that host-egg size serves as the stimulus for multiple egg deposition. He also stated that Trlchogramma are soon exhausted when drilling into hard- shelled eggs, so that parasltization in such eggs is usually less than on smaller thin-shelled eggs. Time also proved to be a contributing factor; parasites spent considerably more time examining and ovipositing in the eggs of T. ni.

Age-specific parasltization curves are presented in Figures 1-3. Even though the parasites exhibited similar patterns on both host eggs,-there was a considerable difference in the number of eggs parasitized; The steep curves are indicative of high initial activity; the Trlchogramma parasitized more eggs during the -first two days of adult life. A definite progressive decrease in the mean number of eggs parasitized dally occurred as the parasites increase in age. The steep curves are also indicative of reduced adult longevity.

Age-specific fecundity curves are shown in Figure 4-6. These curves show that daily fecundity was also affected by

Parasitization

Rate

(px)

17

P . gossyplella0.90px

0.80Px

0.70

50 0.60

0.5040

0.40

25 0.3020

0.201510 0.105

x

Age in DaysFigure 1. Survival and age-specific parasitization curves

for Trichogramma sp, on the eggs of Pectinophoragossypiella and Trichoplusia ni at 68XF.

Survival

Rate

(1

Parasitization

Rate

(px)

18

P . gossyplella0.90Px

0.80Px

0.70

50

40 0.5035 H

0.4030

25 0.3020

0.20

10 0.105


for Trichogramma sp. on the eggs of Pectinophoragossyplella and Trichoplusia ni at 75"° .

Survival

Rate

(l

19

-fv_.P . gossypiella

0.90oPx

Dl0.80Px

0.70

50 0.600)-p(dco•H-PCON•P•HCOCOuCO

0.50H

0.40

0.3020

0.20

10 0.10


for Trichogramraa sp. on the eggs of Pectinophoragossypiella and Trichoplusia ni at 83Wi

Survival Rate

(lx)

Fecundity

Rate

(mx)

20

P . gossyplella0.90

0.80

0.70

0.60

0.50H

0.40

0.3020

0.20

10 0.10

Age in DaysFigure 4. Survival and age-specific fecundity curves for

Trichogramma sp. on the eggs of Pectinophoragossyplella and Trichoplusla nl at 68°F.

Survival

Rate

(lx)

Fecundity

Rate

21

P. gossypiella0.90

0.80□ m

0.70

x 50 0.60

40

350.40

30

0.3020

0.20

10 0.105


Trlchogramma sp. on the eggs of Pectinophoragossypiella and Trichoplusla ni at 75°F.

Survival

Rate

(lx)

Fecundity

Rate

(mx)

22

P . gossypiella

d 1 □ m 0.80

0.70

0.60

0.50

H0.40

= 0.3020

« 0.20

10 0.10L3


Trlchogramma sp. on the eggs of Pectinophoragossypiella and Trichoplusia ni at

Survival

Rate

(lx)

23the host egg. Regardless of the Incubation temperature more progeny were produced by T. nl eggs. Again, as In the case of age-specific parasltization, the difference was more pronounced during the first few days of adult life.

Population Growth A population increases because of the favorable inter

action of many factors present in the environment. In this study the host egg proved to be a 'definite factor influencing population increase of T. sp.

An examination of the population parameters presented in Table 4 shows that the intrinsic rates of increase (rm ), net reproduction rates (P0) and finite rates of increase (X) were considerably greater for parasites reared in the eggs of T. ni at all temperatures. Mean generation times were also lower for parasites developing in T. ni eggs in 'all cases.

• Comparative data presented in Table 2 and age-specific fecundity curves shown in Figures 4-6 indicate that both total fecundity and age-specific fecundity were affected by the host egg. Since population increase is partially dependent on these two attributes, it is necessary to consider host influence when evaluating population increase of the parasite. Both total fecundity and age-specific fecundity were higher in the eggs of T. ni. This indicates that the eggs of T. ni were superior over the eggs of P. gossyplella for population increase of the Trichogramma.

Temperature Influence on the Biology and Population Growth of Trlchogranroia sp.

Effects on Developmental Period Comparative data on the duration of the immature

period of T. sp. developing in the two different host eggs at the various constant temperatures are presented in Table 1.

- The developmental period ranged from 25.8 _+ 2.2 days to 9.1 5 0.5 days for parasites developing in the eggs of P. gossypiellaj and from 24.6 *■ 4 days to 7.8 +_ 0.-9 days forthose developing in the eggs of T. ni at 59° anc 830F.i respectively. No development occurred at 95°F• in either host egg..

/'These results indicate that increased temperature enhanced parasite development, but only until a critical temperature was attained, between 83° and 95°F., which reversed the response and resulted in a detrimental effect on the developing larvae.

Effects on Survival Rate and Adult Longevity The results presented in Table 2 indicate that -

temperature had a definite influence on the survival rate and longevity of the parasites.

Adult longevity for parasites reared on P. gossypiellaeggs ranged from 5.7 ± 2.1 days to 0.2 +_ 0.1 day. and from 5.72 1,6 days to 0.2 0.1 day for parasites reared on T. ni eggs

' 25at 68° and 95°P-^ respectively. It is evident in Table 2 that adult longevity is inversely related to the incubation temperature. The higher the temperature the shorter the adult life of the Trichogramma.

Survival curves are presented in Figures 4-6. These also demonstrate the usual inverse relationship between longevity and temperature. This is indicated by the increased steepness in the curves with increased temperature.

Adult mortality was greatest at 83°F. A temperature of 68°F. resulted in the lowest mortality rate. This indicates that higher temperatures were more detrimental to parasite survival than lower temperatures, even though simple statistical tests failed to reflect any significant differences in survival attributed to the host.

Effects on Fecundity A summary of Trichogramma fecundity data at the

various constant temperatures appears in Table 2.Relative productivity was based on records of 30

parasites at each temperature. The results clearly indicate that temperature did exert an influence oh fecundity. The parasites were more prolific at 75°E•.» which proved to be optimum for egg production on both host eggs. Parasite, productivity decreased considerably when subjected to ternera- tures above or below 75°E. A temperature of 68°F. resulted in the second greatest total fecundity. The lowest fecundity

26occurred at 83°F., and at 95°F. there was no reproduction.The low fecundity in the latter two cases was due to the detrimental effects of temperature on parasite activity and longevity.

A definite influence was also evident in the fecundity patterns or age-specific fecundity schedules. An examination of Figures 4-6 shows that the fecundity curves increased in steepness as the temperature increased, indicating that parasite activity was greater at the higher temperatures. At 68°F. the fecundity curve extends over a longer period due to the low. activity of the parasites and increased adult longevity. The age-specific fecundity curve at 83°F. is more steep and compact. This type of curve is indicative of increased activity and short adult longevity. The highest initial activity occurred at 75°F., accounting for the highest total fecundity and the steepness in the curve, particularly during the first few days of adult life.

Regardless of the temperature, similar fecundity patterns were exhibited on both host eggs, characterized by a high initial activity shortly after emergence. As for the distribution of the egg-laying period throughout the lives of the parasites included in this study, it may be stated that the number of progeny produced daily varied directly with the temperature, the oviposition period tending to lengthen at the lower temperatures and to shorten at the

. . . 27higher'temperatures. Any variation from the optimum reduced the number of progeny produced by the parasites.

Effects on Population Increase

Population increase is dependent on a combination of biological variables which determine the success of an organism to increase in numbers. Among the most important of these are: developmental period; immature mortality, age- specific fecundity and mean progeny produced per female. Not only are the progeny per female important but, also the age- specific fecundity pattern during the life of the reproducing female. Eggs that are produced early in the female's life contribute much more to population increase than those produced later.

.Survival of the offspring also determines to a large extent the capacity of the population to increase. Because, of the importance of offspring produced early in the female's reproductive life, early mortality exerts a more severe effect on population growth than late mortality.

Andrewartha and Birch (1954) state that relatively small changes in one or another component of the environment may result in enormous differences in the animal's innate capacity to increase in numbers, Environments rarely remain constantly favorable or unfavorable, but fluctuate between two extremes. The animal's innate capacity for increase fluctuates correspondingly. ' ■

28Temperature is an important component of any environ

ment and is also an important factor influencing the capacity of an animal to increase. Temperature within the favorable range will create a. favorable condition for population growth. Temperature outside this range will have a detrimental effect.

; In the present study temperature proved to be a definite factor affecting population increase. Data obtained were utilized to construct modified life-fecundity tables from which certain population parameters were calculated. In this approach immature mortality was considered negligible, so that the entire population was assumed to be present on the first day of adult life.

The net .reproduction rate (R0), mean generation time (T), intrinsic rate of increase (rm ), and finite rate of increase (A ) were calculated for the parasites reared at the various constant temperatures. These population parameters are presented in Table, 3.

An examination of the section comparing the rm 's indicates that the greatest population increase occurred at 83°F.; however, the net reproduction rate (R0) was higher at both 68° and 75°P. A temperature of 75°F. resulted in the second highest rm value.' The lowest rm value .occurred at 68°F.

TABLE 3

COMPARATIVE POPULATION PARAMETERS OF TRICHOGRAMMA SP. ON THE EGGS OF PECTINOPHORA GOSSYPIELLA.AND TRICHOPLUSIA NI AT VARIOUS CONSTANT TEMPERATURES

Temp. (°F. )

Ro T (Days) rm IP. gossy-r piella T . ni

P. gossypiella T. ni ■

P. gossypiella T. nl

P. gossypiella T. nl

680 48.07 78.21 16.76 16.96 0.231 0.257 ■ 1.26 1,29 .

75° 55-20 91.07 12.73 11.59 0.315 0.389 1.37 1.47

83° 42.99 59-22 10.50 9.49 0.358 0.430 ' 1.43 1.54

95° —-- . — — — -- —-- —- ---•

rovo

30An analysis of the net reproduction rates ,(R0) shows

that temperature exerted a definite influence on parasite productivity. The highest R0 occurred at 75°F. This indicates that 75° was the optimum temperature for reproduction. The lowest R0 occurred at 830ii\, primarily due to the effects of temperature on parasite longevity and associated fecundity. A temperature of 68°F. resulted in a value midway between that at 75° and 83°F•

The mean generation time (T) was also affected by temperature. The speed of development increased with increased temperature. The optimum temperature for parasite development was 83°F. The longest mean generation time occurred at 68°F. . '1 . Differences in the mean generation times of the parasites at the various temperatures departed from the trend of the R g 's. The trend was not consistent for the intrinsic rates of increase. As noted above, the highest rm occurred at 83°F. despite the fact that at 83°F. the lowest R0 was exhibited. However, the. trend was consistent between the temperatures of 68°F. and 75°F., indicating, that 75°F. was more favorable for population increase than 68°F. The longer mean generation times at 68°F. and/75°F. minimized the value of the intrinsic rates of increase in spite of the higher Rq ..' s . The irregularity in the trend between ■750F • and-83°F., was primarily the result of the longer mean generation time that occurred at 75°F.'

. 31Probably the most Important parameter that describes

population Increase is the finite rate of natural increase ( X. ). This is the multiplication per female in unit time. Quite small differences in the values of X. will cause great variations in the numbers which would occur after several generations.

An examination of the section on X , indicates that the finite' rates of increase were also affected by the temperature. The greatest finite rate of increase occurred at 83° and the lowest occurred at 68°F.

SUMMARY

Effects of the host ■•’and temperature on the biology and- population increase of Trichogramma sp. were studied in the laboratory.

i The host egg influenced population increase by affecting the developmental period and adult fecundity. Both total fecundity and age-specific fecundity were greater in the eggs of Trichoplusia ni. However, total parasitization and age-specific parasitization were higher in the eggs of. Pectinophbra gossypiella, attributed to the fact that only one parasite egg was placed per ]?. gossyplella egg, while several eggs were placed per T. ni egg. Therefore, the parasites were exhausted sooner when attacking T. ni eggs.

Parasites developing in the eggs of T. ni_ -emerged sooner than those in the eggs of P_. gossyplella, regardless of the temperature. Differences were more pronounced at the higher temperatures.-

The eggs of T. ni were better host eggs than the eggs of T ' gossyplella for population growth. The intrinsic rates of increase (rm ), net reproduction rates (R0), and finite rates of increase were higher for parasites reared in T. ni eggs at all temperatures.

3-2

33Temperature influenced population growth primarily

by affecting adult fecundity and longevity. The greatest total and age-specific fecundity occurred at 75°F• which proved to be the optimum temperature for both parasitization and productivity on both host eggs. Temperatures deviating from the optimum resulted in considerable reductions in both parasitization and productivity.

Adult longevity was inversely related to the incubation temperature. Parasites reared at the lower temperatures lived longer. The optimum temperature for longevity was 68°F.. The least favorable was 95°F•

A constant temperature of 83°F. proved to be the most favorable for population increase. The highest intrinsic (rm ) and finite ( L ) rates of increase occurred at this temperature in spite of the fact that the net reproduction rates (R0) were higher at 68° and 75°F. The considerably longer mean generation times (T) that occurred at the latter temperatures minimized the intrinsic rates of increase, regardless of the high net reproduction rates.

■ APPENDIX

LIFE-FECUNDITY TABLES

34

TABLE A ' \MODIFIED LIFE-FECUNDITY.TABLE FOR TRICHOGRAMMA SP„ ON

THE EGGS OF PECTINOPHORA GOSSYPIELLA AT 68° F.

x : ix ;mxl/ ixmx -

Provisional

e. ■ ■ . 0.24 ■■ ; 0.23

7-rx e7~r^. e7-r^lA rx 7-rx e7-rx e7-rxlp.

0-15 — _ — mm we ew16 1.00 23.83 23.83 3.84 3.16 23.57 561.67 3.68 3.32 27.66 659.14 .17 1.00 12.10 12.10 4.08 2.92 18.54 224.33 3.91 3.09 21.98 . 265.9618 1.00 ;6.:60 •.6:60 4.32 2.68 14.59 92.29 4.14 2.86 17,46 115.24 .19 0.90 3.74 3.37 4,55 2.45 11.59 39.05 4.37 2.63 13.87 46.7420 0.77 1.83 1.41 4.80 2.20 . 9.03 12.73 4.6o 2.40 11.02 15.5421 0.43 0.76 0.33 5.04 1.96 7.10 2.24 4.83 2.17 8.76 2.8922 0.23 1.00 0.23 5.28 1.72 5.58 1.28 5.06 1.94 6.96 I.6023 0.10 3.50 0.35 5.52 1.48 4.39 1.54 5:29 ■ 1.71 5.53 1.9424 0.03 5.00 0.15 5.76 1.24 3.46 0.52 5.52 1.48 4.39 0.6625 0.00 0,00 0.00 , — — — ' -- — — — —1 — — — —

R0 = 48.07 Total 935.65- Total 1109.71rm = 0.231T = 16.76

1.26

1/ Age specific fecundity rate (nix) is equal to the age-specific oarasitization rate (px)•‘ ■■ 1 '■ ■ ■ ■ ' : ■■■■ s

TABLE BMODIFIED LIFE-FECUNDITY TABLE FOR TRICHOGRAMMA SP. ON

THE EGGS OF TRICHQPLUSIA Nl AT 68° F. .

Provisional rm 's

X 'Ix Px!/ m^g/ -*-xmx 0.26 0.25rx 7-rx e7-rx e7-rx]A rmx 7-rx e7-%% e7-%xlK

0-15 mmm we 0- we we

. 16 1.00 12.90 32.51 32.51 4.16 2.84 17.13 556.90 4.00 3.00 20.09 653.1317 1.00 8.20 20.66 20.66 4.42 2.58 13.20 272.71 4.25 . 2.75 15.64 323.1218 0.93 5.50 13.86 12.89 4.68 2.32 10.18 131.22 4.50 2.50 12.18 157.0019 0.90 3.48 8.77 7.89 4.94 2.06 7.85 61.94 4.75 2.25 9.49 74.8820 0.77 1.13 2.85 2.18 5.20 1.80 6.05 13.25 5.00 2.00 7.39 . 16.1821 0.37 1.50 3.78 1.39 5.46 1.54 4.66 6.48 5.25 1.75 .5.75 7.9922 0.27 0.88 2.22 0.59 5.72 1.28 3.60 ' 2.12 5.50 1.50 4.48 2.6423 0.17 0.20 0.50 0.09 5.98 1.02 2.77 0.25 5.75 1.25 . 3.-49 0.3124 0.17 0.00 0.00 0.00 — — — — - - - - — ~ — — — _

25 0.03 0.00Rq = rm = T =

0.0078.210.25716.961.29

0.00Total.1044.87 Total 1235.25

1/ Px = age-specific parasitization rate.2/ Corrected age-specific fecundity rate (px x ave. progeny per host egg).

TABLE CMODIFIED LIFE-FECUNDITY TABLE FOR TRICHOGRAMMA SP.ON.THE EGGS OF’PECTINOPHORA GOSSYPIELLA AT 75° F.

Provisional rm 'sX Xx 'mx V <i— 1 . O .32 0.31

47 7-rx e7-r;xl/4 47 7-rx e7-4xl/4

0-1112 1.00 .28.63 28.63 3~84 3.16 23.57 674.81 3.72 3.28 26.58 ' 760.9913 0.97 12.10 11.73 4,16 2.84 17.12 2 0 0 : 8 2 4,03 2.97 19.49 228.6214 0.93 7*46 '6.93 4.48 2.52 12.43 •86.14 4.34 2.66 14.30 ' 99:1015 0.83 7 . 1 6 5.94 4.80 .2,20 ' 9.03 53.64 4.65 2.35 10.49 62.3116 0.47 2.42 1.14 5.12 1.88 6,55 7.47 4.96 2.04 7.69 8.7717 0.37 2 . 0 0 0.74 5.44 1.56 4.76 3.52 5.27 1.73 5.64 4.1718 0 . 2 7 0.37 0.09 5.7'6- 1.24 3.46 0.31 ' 5.58 1.42 4*14 0.3719 0.17 0 . 0 0 0 . 0 0 , •— • 7 — — .*** «a* ~

20 0.07 0 . 0 0

No - rm - T ■ -

0 . 0 055.200.315

12.731.37

Total 1026.71 Total 1164.33'

1/ Age-specific fecundity rate (mx ) is equal to the age-specific parasitization rate (px ). .

TABLE DMODIFIED LTFE-FECUNDLTy TABLE” FOR TRICHOGRAMMA SP„ ON

THE EGGS OF TRICHOPLUSIA NlA T 75a~T7~

Provisional rm '1 s 1

Xi x Pxi/ •*"xmx 0 . 3 9 0 . 3 8

7-r ce 7 - S ?

e 7 - rx l rn x e7-£x e 7 - r x l m *

0-1011 1.00 1 9 . 9 7 4 9 . 9 3 4 9 . 9 3 4 . 2 9 2 .7 1 1 5 . 0 3 7 5 0 . 4 5 4 . 1 8 2.82 16.78 837.8212 0 . 9 7 ' 9 . 4 5 2 3 . 6 2 2 2 .9 1 4 . 6 8 2 . 3 2 1 0 . 1 8 2 3 3 .2 2 4 . 5 6 2 . 4 4 11 .47 262.7813 0 . 8 7 4 . 6 2 1 1 . 5 5 1 0 . 0 5 5 . 0 7 1 . 9 3 . 6 . 8 9 6 9 . 2 4 4 . 9 4 2 . 0 6 7 . 8 5 7 8 . 8 914 0 . 7 7 3 . 3 0 8 . 2 5 6 . 3 5 5 . 4 6 1 . 5 4 4 . 6 6 2 9 . 5 9 5 . 3 2 1.68 5 . 3 7 3 4 . 1 015 0 . 4 7 1.21 3 . 0 3 1 . 4 2 . 5 . 8 4 1 . 1 6 3 . 1 9 4 . 5 3 5 . 7 0 1 . 3 0 3 .6 7 5.2116 0 . 4 0 0 . 2 5 0 . 6 2 0 . 2 5 6 . 2 4 0.76 2 . 1 4 0 . 5 4 6 . 0 8 0 . 9 2 2 .5 1 0.6817 0 . 2 3 0.28 . 0 . 7 0 0 . 1 6 6 . 6 3 0 . 3 7 1 . 4 5 0 . 2 3 6 . 4 6 0 . 5 4 1.72 0.2818 0 . 1 7 0.00 0.00 0.00 — — — — — — — — — — — — w * —

19 0 . 0 7 ' 0 . 0 0 0.00 0.0020 0 . 0 3 0.00

■ R 0 z rm 2 T =

0.009 1 . 0 7

0 . 3 8 91 1 . 5 9

1 . 4 7

0.00Total 1087.80 Total 1 2 1 9 .7 1

1/ Px - age-specific fecundity rate.2/ Corrected age-specific fecundity rate (px xave. progeny per host egg).

U)00

TABLE EMODIFIED LIFE-FECUNDITY TABLE FOR TRICHOGRAMMA SP. ONTHE EGGS OF PECTINOPHORA GOSSYPIELLA at:03° p . •

Provisional rm !'s

X 1.x ®xl/ . lxmx O .36 0.35

rx 7-rx eT-rx e7-rx3xrnx 7-%% e7-rx e7-rx]xnv

0- 910 1.00 24.53 24.53 3.60 3.40 29.96 734.92 3.50 3.50 33.12 812.4311 0.97 12.86 12.47 3.96 3.04 20 . 91 260.75 3.85 3.15 23.34 291.0512 0.8o 6.25 5.00 4.32 . 2.65 14.15 70.75 4.20 2.80 16.45 82.25

' 13 0.43 1.25 0.53 4.68 2.32 10.18 5.39 4.55 2.45 11.59 6.1414 0.10 0.67 0.07 5.04 1.96 7.10 0.50 4. g o 2.10 8.17 0.5715 0.07 0.00

rRl =t = :

0.0042.99 0.358 10.50 1.43 .

Total 1072.31 Total 1192.44

i/ Age specific' .fecundity rate (m ,) is equal to the age-specific parasitization rate (px ). z

uoxo

TABLE PMODIFIED LIFE-FECUNDITY TABLE FOR TRICHOGRAMMA SP. ON

THE EGGS OF TRIOHOPLUSIA NI AT.83° P.

P x ^ m x 2/' Provisional .rjn1 s

X lx 1 xmx 0.44 0.43<rx 7-rx e7-%K e7-rxl^ rx 7-rx ,g7~rx e7-rxlp%

0- 89- 1.00 16.13 35.16 35.16 3.96 3-04 20.91 735.20 3.87 3.13 22.87 804.11

10 0.93 6.46 14.68 13.09 4.40 2.60 13.46 176.19 4.30 2.70 14.88 194.7811 0.77 5.34 11.64 8.96 . 4.84 2.16 8.67 77.68 4.73 2.27 9.68 86.7312 0.40 2.00 4.36 1.74 5.28 1.72 5.58 9.71 5.16 1.84 6.30 10.9613 0.10 1.25 2.73 0.27 5.72 1.28 3.60 0.97 5.59 1.41 4.10 1.1114 0.00 0.00

Ro = rm - T z

0.0059.22 . .430 9.49 1.54

0.00. Total 994.75 Total 1097.69

1/ px = age-specific parasitization rate2/ Corrected, age-specific fecundity rate (px x ave. progeny per host egg) .

LITERATURE CITED

Andrewartha, H. G. and L. C . Birch. 1954. The distributionand abundance of animals. The University of Chicago Press, Chicago, pp. 31-54.

Birch, L. C. 1948. The intrinsic rate of natural increase of an insect population. J. Ahlm. Ecol. 17(!):

. 15-26.Lund, H. 0. 1938. Studies on longevity and productivity

in Trichogramma evanescens. J. Ag. Research. 56: 421-39.

Salt, G. 1941. The effects of the host upon their insect parasites. Biol. Rev. 16:239-364.

Shorey, H. H. 1963. A simple artificial rearing medium for the cabbage looper. J. Econ. Entomol. 56(4):'536-537.

Quednau, W. i960. Uber die identitat der Trichogramma-Arten und einiger Okotypen (Hymendptera, Chalcidoidea, Tri'chogrammatidae) Mitt. Biol. Bundesasnst.Berlin-Dahlem 100:11-50.

Watson, T. P. 1964. Influence of host plant condition on population increase of Tetranychus telarius (Linnaeus) (Acarina: Tetranychidae). Hllgardia 35(11):263-322.

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