Insect‐resistant transgenic plants in a multi‐trophic context

Abstract

Summary So far, genetic engineering of plants in the context of insect pest control has involved insertion of genes that code for toxins, and may be characterized as the incorporation of biopesticides into classical plant breeding. In the context of pesticide usage in pest control, natural enemies of herbivores have received increasing attention, because carnivorous arthropods are an important component of insect pest control. However, in plant breeding programmes, natural enemies of herbivores have largely been ignored, although there are many examples that show that plant breeding affects the effectiveness of biological control. Negative influences of modified plant characteristics on carnivorous arthropods may induce population growth of new, even more harmful pest species that had no pest status prior to the pesticide treatment. Sustainable pest management will only be possible when negative effects on non‐target, beneficial arthropods are minimized. In this review, we summarize the effects of insect‐resistant crops and insect‐resistant transgenic crops, especially Bt crops, from a food web perspective. As food web components, we distinguish target herbivores, non‐target herbivores, pollinators, parasitoids and predators. Below‐ground organisms such as Collembola, nematodes and earthworms should also be included in risk assessment studies, but have received little attention. The toxins produced in Bt plants retain their toxicity when bound to the soil, so accumulation of these toxins is likely to occur. Earthworms ingest the bound toxins but are not affected by them. However, earthworms may function as intermediaries through which the toxins are passed on to other trophic levels. In studies where effects of insect‐resistant (Bt) plants on natural enemies were considered, positive, negative and no effects have been found. So far, most studies have concentrated on natural enemies of target herbivores. However, Bt toxins are structurally rearranged when they bind to midgut receptors, so that they are likely to lose their toxicity inside target herbivores. What happens to the toxins in non‐target herbivores, and whether these herbivores may act as intermediaries through which the toxins may be passed on to the natural enemies, remains to be studied.

Awareness of Hormesis Will Enhance Future Research in Basic and Applied Neuroscience

“…Because vegetables and fruits have high concentrations of antioxidants such as vitamins E and C, it is believed that most beneficial chemicals in these foods act by decreasing oxidative stress. However, work in this and other laboratories suggest that some phytochemicals are toxins that serve the function of protecting the plants against insects and other predators (Groot and Dicke, 2002;Trewavas and Stewart, 2003;Mattson and Cheng, 2006). Such phytochemicals can induce a mild adaptive stress response in cells.…”

Tailoring the Specificity of a Plant Cystatin toward Herbivorous Insect Digestive Cysteine Proteases by Single Mutations at Positively Selected Amino Acid Sites

“…Optimizing the inhibitory specificity of recombinant cystatins toward target pests also could prove attractive from an ecological viewpoint, considering the complex multitrophic interactions known to take place at the ecosystem level (Groot and Dicke, 2002). The ability of recombinant plant cystatins to inhibit the digestive Cys proteases of insect predatory arthropods via their herbivorous prey fed the modified plant has been documented recently (Bouchard et al, 2003a(Bouchard et al, , 2003bFerry et al, 2003;Alvarez-Alfageme et al, 2007), thus stressing the importance of not only monitoring protease: inhibitor interactions expected to take place between the plant and its herbivorous enemy but also to assess the interactions likely to occur in the proximate environment.…”

Reduced Fitness of Daphnia magna Fed a Bt-Transgenic Maize Variety

“…Bt-toxin produced in GM-plants has been shown to retain 25-30% of its toxicity after 140 days when bound to soil (Palm et al 1996). Adsorption and binding of Cry proteins to clay sometimes even enhance the insecticidal activity (Tapp and Stotzky 1995), thus increasing the likelihood that bioactive toxin is accumulated in the environment (Groot and Dicke 2002). At the same time, Bt-maize and isogenic controls have been corroborated to be substantially equivalent at the level of major nutrients and minerals and trace elements, both in kernels (Brake and Vlachos 1998;Sidhu et al 2000) and in the whole plant (Clark and Ipharraguerre 2001).…”

“…Many nontarget organisms, including herbivores, pollinators, parasitoids, and predators will directly and indirectly be exposed to transgene products and altered interactions (Andow and Hilbeck 2004;Dutton et al 2003;Groot and Dicke 2002;Hilbeck 2001;O'Callaghan et al 2005) and it is well justified to test these for potential harmful effects. Several reviews cover many groups of invertebrates, but nearly all of the tested species are terrestrial.…”