Date of Award

8-1970

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Entomology

First Advisor

Edwin W. King

Second Advisor

Sidney B. Hays

Third Advisor

A. E. Schwertz

Abstract

An interaction study was conducted between the Indianmeal moth, Plodia 1nterpunctella (Hilbner) (Phyc1t1dae 1 Lepidoptera), and its parasite, Bracon hebetor Say (Bracon1dae1 Hymenoptera), to determine the potential of this wasp as a biological control agent of this stored grain pest. Standardized host colonies of 1800 larvae were established on 600 ml of medium in 1 gal jars and maintained at 27oc, 60% R H, and a constant lighting. Colonies were allowed to develop for 12 days at which time the wasps were introduced at 9 densitiess 0-, 50-, 100-, 150-, 200-, 250-, 300-, 350-, and 400-female wasps. For each 2 females, 1 male was introduced also. The 2 populations were allowed to develop for the duration of a single host generation. At the end of this interaction period, the 2 populations were counted and the degree of host suppression evaluated. Increasing the wasp density progressively decreased the moth population up to the 250-wasp treatment. The wasps appeared to have reached their maximum control at this level, since any further density increase did not significantly lower the moth numbers. By introducing a ratio of 1 female wasp per 7 host larvae a 97% control was obtained. Three statistical techniques were used in the analysis of this interaction; one, based on coefficients of orthogonal polynomials and an analysis of variance, a second, based on linear regression and log transformations, and a third which considered the function of decreasing moth populations as the inverse of a growth curve, and led to a logistic analysis of the mortality of the moth colonies. The effect of the interaction on the sex ratios of the moths and wasps was studied also. As the parasite density was increased, the percentage of moths which were females was gradually decreased from its normal of 52% and a sign1f ica.nt linear response was found. The resulting wasp sex ratio was also affected. Even though the total wasp population was not s1gnif icantly changed, the corresponding female percentage was. A quadratic response was significant and the highest female wasp percentage was found at the 250-wasp density. It may be concluded from these tests that B. hebetor has a significant suppression rate on its host and the best control is produced at a ratio of 1 female wasp per 7 host larvae.

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