Abstract
Insect resistance to population control methodologies is a widespread problem. The development of effective resistance management programs is often dependent on detailed knowledge regarding the biology of individual species and changes in that biology associated with resistance evolution. This study examined the reproductive behavior and biology of western corn rootworm beetles of known body size from lines resistant and susceptible to the Cry3Bb1 protein toxin expressed in transgenic Bacillus thuringiensis maize. In crosses between, and within, the resistant and susceptible genotypes, no differences occurred in mating frequency, copulation duration, courtship duration, or fertility; however, females mated with resistant males showed reduced longevity. Body size did not vary with genotype. Larger males and females were not more likely to mate than smaller males and females, but larger females laid more eggs. Moderately strong, positive correlation occurred between the body sizes of successfully mated males and females; however, weak correlation also existed for pairs that did not mate. Our study provided only limited evidence for fitness costs associated with the Cry3Bb1-resistant genotype that might reduce the persistence in populations of the resistant genotype but provided additional evidence for size-based, assortative mating, which could favor the persistence of resistant genotypes affecting body size.
Highlights
The western corn rootworm, Diabrotica virgifera virgifera LeConte, is an important economic pest of maize, Zea mays L., in the United States and more recently in Europe, with an estimated one billion dollars in annual control costs in the U.S alone [1,2,3]
Because pesticide and Cry3Bb1 resistance that carries few fitness costs persists for some generations in the absence of selection [14,34,44], all the lines were reared on non-transgenic maize beginning with F12
Whether the Cry3Bb1-resistant genotype was associated with one or both sexes in mixed-sex pairs established with virgin insects, we detected no effect of resistance on the mating success of the pairs or on the courtship and copulation durations of those pairs that mated successfully
Summary
The western corn rootworm, Diabrotica virgifera virgifera LeConte, is an important economic pest of maize, Zea mays L., in the United States and more recently in Europe, with an estimated one billion dollars in annual control costs in the U.S alone [1,2,3] This insect has repeatedly demonstrated its resilience in overcoming population control attempts by evolving physiological resistance to insecticides [4,5,6,7] and behavioral resistance to crop rotation involving increased oviposition in non-maize fields where hatching larvae may survive if maize is grown the following season [8]. The purpose of this non-Bt refuge is to provide susceptible corn rootworm beetles able to disperse from the refuge and mate with any resistant individuals emerging from the Bt plants, slowing resistance evolution to the Bt toxins and lengthening the effective lifespan of the Bt varieties
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