Impacts of Developing on Bt Maize-Intoxicated Hosts on Fitness Parameters of a Stem Borer Parasitoid

Abstract

Transgenic Bt maize cultivars are widely used in U.S. agriculture. Control of target pests by these cultivars is not complete, and non-target pests are usually tolerant of the toxic activity of these cultivars. Sublethally intoxicated pest individuals may become hosts for parasitoids, but their quality as hosts may be affected as a result of intoxication. This study addresses the effects on various fitness parameters in parasitoids that develop on intoxicated hosts. The parasitoid used in this study was Parallorhogas pyralophagus (Marsh), a gregarious, external idiobiont, and the host was Eoreuma loftini Dyar, a subtropical stemborer. Results showed that ingestion of Bt maize tissue by E. loftini larvae negatively affected some fitness components in P. pyralophagus, whereas other components were not affected. Specifically, immature stage developmental mortality was greater, adult longevity was approximately 1 d shorter in females, and developmental times were approximately 2 d longer in both males and females when P. pyralophagus developed on hosts fed Bt maize tissue relative to hosts fed non-Bt maize tissue. Moreover, parasitoid brood size was positively correlated with host size when hosts were fed non-Bt maize tissue, while this relationship was absent when hosts were fed Bt maize tissue. However, feeding on Bt maize tissue did not affect egg loads, adult size-egg load and adult size-longevity relationships, adult sizes of females and males, and sex ratio of parasitoids whose hosts were fed Bt maize tissue. Results are discussed in relation to the importance of sublethal effects of Bt maize cultivars on parasitoids and potential impacts on naturally-occurring biological control.