Interactions of Bt-cotton and the omnivorous big-eyed bug Geocoris punctipes (Say), a key predator in cotton fields

The continuous expression of the Bt (=Bacillus thuringiensis) toxin in plants during the growing season may bring Bt toxin into contact with the omnivorous big-eyed bug Geocoris punctipes (Say) (Hemiptera: Geocoridae), an important predator in cotton fields, through prey fed Bt-cotton or through plant feeding. Therefore, an experiment was set up during two seasons (2003 and 2004) in the field to assess host plant- and prey-mediated effects on development and reproduction of the predator. We used a combination of Bt and non-Bt cotton plants, and of prey, with one treatment conveying Bt Cry1Ac toxin to the upper trophic level [Spodoptera exigua (Hübner) larvae (BAW)] and the other prey item free of toxin [Helicoverpa zea (Boddie) eggs (CEW)]. This design allowed us to differentiate direct and indirect effects of the toxin in the host plant from effects attributable to prey quality under field conditions. The experiment began with newly hatched big-eyed bug nymphs and ending when the last female died. The combination of prey and Bt-cotton plants did not exert interactive effects on development and reproduction of the omnivorous predator. The prey effect was independent of either host plant type. Nymphs fed BAW larvae developed slower and produced smaller adults with no difference between cotton genotypes. Reproductive output and longevity were similar between cottons for both prey types, and were consistently lower for predators fed BAW larvae. Cry1Ac was detected in Bt-cotton and in BAW larvae fed Bt-cotton and offered to the predators, but not in the predators' bodies. The results do not indicate any lethal or sublethal effect of transgenic Bt-cotton or of Cry1Ac conveyed through prey on development and reproduction of G. punctipes in our field experiments.