Modeling the Dynamics of Adaptation to Transgenic Corn by Western Corn Rootworm (Coleoptera: Chrysomelidae)

Abstract

A simulation model of the population dynamics and genetics of the western corn rootworm, Diabrotica virgifera virgifera LeConte, was created for a landscape of corn, soybean, and other crops. Although the model was created to study a 2-locus problem for beetles having genes for resistance to both crop rotation and transgenic corn, during this first phase of the project, the model was simulated to evaluate only resistance management plans for transgenic corn. Allele expression in the rootworm and toxin dose in the corn plant were the two most important factors affecting resistance development. A dominant resistance allele allowed quick evolution of resistance to transgenic corn, whereas a recessive allele delayed resistance >99 yr. With high dosages of toxin and additive expression, the time required to reach 3% resistance allele frequency ranged from 13 to >99 yr. With additive expression, lower dosages permitted the resistant allele frequency to reach 3% in 2-9 yr with refuges occupying 5-30% of the land. The results were sensitive to delays in emergence by susceptible adults and configuration of the refuge (row strips versus blocks).

Long-term regional suppression of pink bollworm byBacillus thuringiensiscotton

“…The long-term regional suppression of pink bollworm reported here may further reduce insecticide use and enhance implementation of the refuge strategy, which is mandated by the U.S. Environmental Protection Agency for delaying evolution of pest resistance to Bt cotton (2)(3)(4)(5)(6)(7)(8). This strategy requires that growers plant refuges of non-Bt cotton to promote survival of susceptible pests.…”

“…Transgenic cultivars of cotton and maize that produce toxins from Bacillus thuringiensis (Bt) to control insect pests were grown on 12 million hectares worldwide during 2001 (1). A major concern is that rapid evolution of resistance by pests could nullify the benefits of Bt crops (2)(3)(4)(5)(6). It has also been proposed, however, that Bt crops imposing high mortality could cause regional suppression of target pests before resistance occurs (6)(7)(8)(9).…”

Modeling Evolution of <I>Diabrotica virgifera virgifera</I> (Coleoptera: Chrysomelidae) to Transgenic Corn With Two Insecticidal Traits

“…Even if emergence is delayed in transgenic insecticidal corn, the last males emerging from refuge corn can mate with females for 30 d or more (Quiring and Timmins 1990). In a simulation study, Onstad et al (2001) concluded that, when sublethal effects of transgenic corn cause susceptible phenotypes to emerge later than normal in a block conÞguration, resistance can evolve faster when resistance is recessive. When resistance is recessive and only homozygous susceptibles are delayed 6 d, the time to 3% resistance allele frequency was shortened in situations in which the insecticidal corn was not very efÞcacious.…”

“…With recessive resistance and both susceptible homozygotes and heterozygotes delayed 6 d, the resistance allele frequency never changed in the 99 yr of using transgenic corn. When the homozygous susceptibles were delayed by 3Ð9 d with additive allele expression, resistance evolution did not change (Onstad et al 2001). Thus, to predict the inßuence of developmental delays, if they exist, on resistance evolution, we must know whether heterozygotes are delayed as well as whether resistance is recessive.…”

“…These studies determined that resistance management is not sensitive to refuge levels between 5 and 20% (Onstad et al 2001, Storer 2003. Because both single and multiple-toxin rootworm-protected hybrids will now be planted in the United States, it is important to increase our understanding of the potential for resistance evolution to occur in this system.…”