Date of Award
Doctor of Philosophy (PhD)
David J. Boethel
Studies were conducted to investigate the influence of both plant resistance and insecticidal controls used in soybean on several natural enemies of pest insects. There were two major objectives to this research: (1) to examine the effects of an insect herbivore-resistant soybean genotype on relationships between four levels of a trophic system; (2) to determine the influence of the primary insecticides applied to control Louisiana soybean insect pests on survival of a major biological control agent of stink bugs. In the first study, pre-imaginal development of the predatory pentatomid, Podisus maculiventris (Say), was affected by soybean antibiosis in a manner similar to that of its lepidopteran prey, Pseudoplusia includens (Walker). Pre-imaginal development time and mortality were increased, and cumulative weight gain reduced on resistant foliage. Reproductive capacity of P. maculiventris reared on P. includens larvae fed resistant soybean generally was unaffected, although progeny production was delayed and extended slightly. Pre-imaginal development and adult emergence of the egg parasitoid Telenomus podisi Ashmead from eggs of P. maculiventris reared on P. includens larvae fed resistant soybean were unaffected. However, overall reproductive capabilities of this parasitoid were reduced. In the second study, adult egg parasitoids, Trissolcus basalis (Wollaston), were minimally affected by permethrin field applications, while methyl parathion had an adverse but short-lived effect on parasitoid survival. High levels of adult mortality were observed only within the first 12 hours following spray application. Neither insecticide affected emergence of parasitoids from their host eggs, suggesting that stink bugs eggs provided a barrier to insecticide penetration. However, parasitoids apparently contacted insecticide residues when chewing through host egg shells to emerge, resulting in some post-emergence mortality caused by methyl parathion. Three factors affected the degree of this mortality: (1) parasitoid developmental stage at time of insecticide application, (2) position of parasitized egg masses in the soybean canopy, and (3) parasitoid gender. Results from these studies suggest the potential for incompatibility of some biological control agents with insect-resistant soybeans, but also demonstrate the compatibility between an important natural enemy and current insecticidal controls applied to Louisiana soybeans.
Orr, David Boyd, "Compatibility of Biological Control With Host Plant Resistance and Insecticidal Control in Soybeans." (1988). LSU Historical Dissertations and Theses. 4526.