Effects of transgenic Bacillus thuringiensis corn-fed prey on mortality and development time of immature Chrysoperla carnea (Neuroptera: Chrysopidae)

Laboratory feeding experiments using transgenic Bacillus thuringiensis variety kurstaki (Berliner) corn plants have been carried out to study the effects of B. thuringiensis-fed herbivores (i.e., prey), on the predator Chrysoperla carnea Stephens. Host plants were a transgenic B. thuringiensis-expressing (Cry1Ab) corn hybrid and the corresponding untransformed, B. thuringiensis-free corn hybrid. Two different prey species were used in the experiments, the European corn borer, Ostrinia nubilalis (Hubner) (lepidopterous target pest), and Spodoptera littoralis (Boisduval) (lepidopterous nontarget pest for B. thuringiensis). The objectives were to quantify the effects of B. thuringiensis-fed prey on chrysopid immature development and to determine whether observed effects were caused by sick, suboptimal prey (indirect effects) or associated with B. thuringiensis-related causes (direct effects). Mean total immature mortality for chrysopid larvae raised on B. thuringiensis-fed prey was 62% compared with 37% when raised on B. thuringiensis-free prey. There was no significant difference in mortality between chrysopid larvae reared on B. thuringiensis-fed O. nubilalis or B. thuringiensis-fed S. littoralis. Similarly, no significant difference in mortality was detected when chrysopid larvae were raised on B. thuringiensis-free O. nubilalis or B. thuringiensis-free S. littoralis. Development time of chrysopid larvae was prolonged when B. thuringiensis-fed O. nubilalis was given to the predators but not for B. thuringiensis-fed S. littoralis. Although some unnoticed adverse effects in S. littoralis may have occurred because of the B. thuringiensis corn, our results suggest that the reduced fitness of chrysopid larvae was associated with B. thuringiensis. The prolonged development time of chrysopid larvae raised on B. thuringiensis-fed O. nubilalis was probably because of a combined effect of B. thuringiensis exposure and nutritional deficiency caused by sick prey.