Location: Integrated Cropping Systems ResearchTitle: Spider mite infestations reduce Bacillus thuringiensis toxin concentration in corn leaves and predators avoid spider mites that have fed on Bacillus thuringiensis corn Author
Submitted to: Annals of Applied Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2014
Publication Date: 6/23/2014
Citation: Prager, S., Martini, X., Guvvala, H., Nansen, C., Lundgren, J.G. 2014. Spider mite infestations reduce Bacillus thuringiensis toxin concentration in corn leaves and predators avoid spider mites that have fed on Bacillus thuringiensis corn. Annals of Applied Biology. 165:108-116. Interpretive Summary: Bt crops express insecticidal toxins (Cry toxins) with a fairly narrow spectrum of activity intended to kill only the targeted pests. Bt corn expresses at least two types of toxins that kill caterpillar (European corn borer) and beetle (corn rootworm) pests. Spider mites are secondary pests that are not directly affected by Bt corn, but are ubiquitous in Bt cornfields, especially in more arid production regions. We found that herbivory by spider mites reduces the quantity of Cry toxins found in Bt corn plants. Also, spider mites that ate the Bt corn tissue aggregated the Cry toxin in their bodies, and were less attractive to predatory mites than those that ate non-Bt corn. These two results present a situation where outbreaks of spider mites in Bt corn fields are less likely to be suppressed by their predators than outbreaks in conventional corn. These mite outbreaks could subsequently make the Bt corn plants less resistant to the targeted pests, the European corn borer and corn rootworm. This research changes our perception of how secondary herbivores fit within GM cropping systems and how they affect insect and pest communities.
Technical Abstract: Transgenic crops containing pyramid-stacked genes for Bacillus thuringiensis derived toxins for controlling coleopteran and lepidopteran pests are increasingly common. As part of environmental risk assessments, these crops are evaluated for toxicity against non-target organisms, and for their potential impact on food-webs. However, environmental risk assessment studies of Bt crops rarely incorporate behavioral responses by arthropods. We examined the behavioral response of an obligate spider mite predator, Phytoseiulus persimilis, when offered spider mites (Tetranychus cinnabarinus) reared on corn with and without Bt toxins. Spider mites were found to accumulate Bt-toxins when reared on Bt-corn, and in choice tests predators preferred spider mites from non-Bt plants. Furthermore, spider mite infested corn exhibited lower toxin levels than non-infested plants. These results affect insect resistance management guidelines and management decisions of secondary pests in Bt corn, and emphasize the need for evaluations of transgenic crops beyond their direct toxicity.