Abstract
The biological control function provided by natural enemies is regarded as a protection goal that should not be harmed by the application of any new pest management tool. Plants producing Cry proteins from the bacterium, Bacillus thuringiensis (Bt), have become a major tactic for controlling pest Lepidoptera on cotton and maize and risk assessment studies are needed to ensure they do not harm important natural enemies. However, using Cry protein susceptible hosts as prey often compromises such studies. To avoid this problem we utilized pest Lepidoptera, cabbage looper (Trichoplusia ni) and fall armyworm (Spodoptera frugiperda), that were resistant to Cry1Ac produced in Bt broccoli (T. ni), Cry1Ac/Cry2Ab produced in Bt cotton (T. ni), and Cry1F produced in Bt maize (S. frugiperda). Larvae of these species were fed Bt plants or non-Bt plants and then exposed to predaceous larvae of the green lacewing Chrysoperla rufilabris. Fitness parameters (larval survival, development time, fecundity and egg hatch) of C. rufilabris were assessed over two generations. There were no differences in any of the fitness parameters regardless if C. rufilabris consumed prey (T. ni or S. frugiperda) that had consumed Bt or non-Bt plants. Additional studies confirmed that the prey contained bioactive Cry proteins when they were consumed by the predator. These studies confirm that Cry1Ac, Cry2Ab and Cry1F do not pose a hazard to the important predator C. rufilabris. This study also demonstrates the power of using resistant hosts when assessing the risk of genetically modified plants on non-target organisms.
Highlights
Green lacewings (Neuroptera: Chrysopidae) are important beneficial predators in many cropping systems [1]
The biological control function provided by lacewings and other natural enemies is regarded as a protection goal that should not be harmed by the application of any new pest management tool [2,3]
The impact of insect-resistant genetically engineered (GE) plants that produce Cry proteins derived from the bacterium Bacillus thuringiensis on valued non-target arthropods should be addressed in the ecological risk assessment that precedes the commercial release of any new GE plant
Summary
Green lacewings (Neuroptera: Chrysopidae) are important beneficial predators in many cropping systems [1]. The test substance can be mixed with non-GE plant material or provided in the form of GE plant material Predatory species such as lacewing larvae can be exposed to the plant-produced Cry proteins through GE-plant fed herbivores that are used as prey. While the latter case has the advantage of providing a very realistic exposure pathway, it carries the risk that the herbivores themselves are affected by the test substance and effects seen on the predator may be due to a lower prey quality rather than a direct effect of the plant-produced Cry protein Such so-called ‘prey-quality mediated effects’ have been observed in numerous tri-trophic feeding studies with Bttransgenic crops [7,8] and have erroneously been interpreted as direct toxic effects of the Cry proteins [9,10,11,12]. Resistant strains of Lepidoptera have been used to assess the impact of particular Cry proteins in Bt plants on several natural enemies, including Chrysoperla carnea (Neuroptera: Chrysopidae) [13], Coleomegilla maculata (Coleoptera: Coccinellidae) [14,15], Pterostichus madidus (Coleoptera: Carabidae) [16], and the parasitoids Diadegma insulare (Hymenoptera: Ichneumonidae) [17] and Cotesia plutellae (Hymenoptera: Braconidae) [18]
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