Submitted to: Journal of Applied Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2004
Publication Date: N/A
Interpretive Summary: Today, genetically-engineered cottons contain a gene that is detrimental to certain caterpillar pests. These cotton varieties (called transgenic Bt) are now planted across numerous acres in the southern United States. These transgenic systems are quite ecologically complex. While they do control serious pests in cotton, researchers are often left to determine the effects on beneficial insects (i.e. "good" insects that normally prey on the pest species). In addition, previous studies suggest that the constant exposure to the Bt in transgenic cotton may cause a build up of individuals that are resistant (i.e. cannot be controlled any longer). Thus, it is widely suggested that an area of cotton be set aside (i.e. called a refuge strategy) that does not contain Bt to insure that a sufficient number of moths remain susceptible and can mate with any resistant moth. Thus, the progeny would then be susceptible. Indeed these ecological parameters are complex, and often computer models are used to simulate the long-term probability for developing resistance (often termed "resistance management"). Our study shows that without planting a refuge, resistance would develop quite quickly (ca. a few years) in certain caterpillar pests. In addition, the reduction of beneficial insects in Bt cotton, by whatever means, would also cause resistance to develop quickly.
Technical Abstract: The value of natural enemies in cotton has been widely recognized for the control of noctuid pests such as bollworms and defoliators. A realistic physiologically based age-mass structured model of Bt cotton and pink bollworm is extended to include bollworm, beet armyworm, the effects of generalist natural enemies on pest dynamics, and the effects of the Bt toxin on plant-herbivore interactions and the development of resistance. A simulation model is used to show the regulating effects of natural enemies on noctuid pests in conventional and Bt cottons with and without spatial refuges for susceptibility to Bt toxin. Without spatial refuges, resistance to Bt toxin develops rapidly in beet armyworm despite the temporal refuge created by its tolerance to the toxin. Natural refuges in the form of non Bt hosts are present for both pests and moderate immigration of susceptible individuals from them suppresses the development of resistance. However, insecticides use and the suppression of natural enemies may enhance resistance development. The model suggests that outbreaks of noctuid pests are possible due to trade-offs between increased levels of resistance, the effects of the toxin on pest vital rates, and pesticide use that further diminishes natural enemy efficacy.