Genetically Modified Crops and Biological Control with Egg Parasitoids

Abstract

Genetically-modified (GM) crops presently are central components of pest management strategies for several important crops worldwide. GM crops include insect-resistant varieties (expressing transgenes from the bacterium Bacillus thuringiensis, or from plant species other than the GM crop, though only the former varieties are commercially available), and herbicide-tolerant varieties (which tolerate post-emergent applications of particular herbicides). This chapter examines potential and known impacts of GM crops on egg parasitoids. Egg parasitoids can be affected by insect-active toxins or proteins produced by insect-resistant GM crops, or by herbicides applied to herbicide-tolerant crops. A review of the literature showed that very little research has addressed the impacts of GM crops on egg parasitoids, compared to the research on larval parasitoids or predatory insects. The amount and focus of research involving egg parasitoids, though, may be subject to existing factual prejudices: (i) the presence of toxins from insect-resistant varieties in herbivore eggs used as hosts by egg parasitoids is improbable, and (ii) the target of herbicide-tolerant varieties is weeds, by way of herbicide applications. However, egg parasitoids can be affected by GM crops through infrequently explored, direct or indirect pathways, such as exposure to GM crop toxins in honeydew or nectars, or pauperization of host populations in insect-resistant crops or of flowering plant communities in herbicide-tolerant crops. These pathways of GM crop effects on egg parasitoids are likely the most important, but have not been adequately addressed. A fuller understanding of any effects of GM crops on egg parasitoids is particularly significant in the context of analyses pointing to the importance of movement of natural enemy populations among crops and between seasons within a landscape, for pest management and biological control at regional scales.