Correlation Between Behavioral and Physiological Responses to Transgenic Potatoes Containing Bacillus thuringiensis δ-Endotoxin in Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

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Abstract
Proposed resistance management strategies for Colorado potato beetle, Leptinotarsa decemlineata (Say), in transgenic potato crops containing Bacillus thuringiensis 8-endotoxin include growing a mixture of transgenic and nontransgenic seed. The success of the strategy would be affected by behavioral responses of Colorado potato beetle to the transgenic foliage in a mixture, and the correlation between behavioral response and physiological resistance. We reared full-sib families of Colorado potato beetle larvae from single mated pairs and measured behavioral response and physiological susceptibility of larvae from each family to transgenic foliage. The behavioral assay consisted of a graded series of endotoxin concentrations, given by potato lines with different endotoxin expression levels. The physiological assay consisted of a single small transgenic leaf disk containing a dose estimated to be approximately the LD50 for the parent generation. Significant genetic components were observed in the variation in both characters. Heritability estimates were particularly high for the physiological response. The correlation between the two characters was significant. More behaviorally responsive larvae tended to be more physiologically resistant. The implications for the seed mixture strategy are that larvae moving onto transgenic foliage in a mixture are more likely to return to the non transgenic foliage if they are more resistant; indirect selection for physiological resistance could result. Because indirect selection for physiological resistance is possible for adult beetles as well as larvae, similar studies should be conducted on adults. The assumed benefits of seed mixtures, providing a refuge for susceptible beetles, also should be verified.

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