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  1. Abstract BACKGROUND

    Agricultural insect pests frequently exhibit geographic variation in levels of insecticide resistance, which are often presumed to be due to the intensity of insecticide use for pest management. However, regional differences in the evolution of resistance to novel insecticides suggests that other factors are influencing rates of adaptation. We examined median lethal concentration (LC50) bioassay data spanning 15 years and six insecticides (abamectin, imidacloprid, spinosad, cyantraniliprole, chlorantraniliprole, and metaflumizone) for evidence of regional differences inLeptinotarsa decemlineatabaseline sensitivity to insecticides as they became commercially available.

    RESULTS

    We consistently found that larvae from Colorado potato beetle populations from the northwestern USA had the highest baseline sensitivity to novel insecticides, while populations from the eastern USA had the lowest. Comparisons of gene expression between populations from these regions revealed constitutively elevated expression of an array of detoxification genes in the East, but no evidence of additional induction when exposed to imidacloprid.

    CONCLUSIONS

    Our results suggest a mechanism for geographic variation in rates of adaptation to insecticides, whereby baseline levels of gene expression determine a population's response to novel insecticides. These findings have implications for the regional development of insecticide resistance management strategies and for the fundamental question of what determines the rate of adaptation to insecticides. © 2020 Society of Chemical Industry

     
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  2. Abstract

    Evolutionary radiations have been well documented in plants and insects, and natural selection may often underly these radiations. If radiations are adaptive, the diversity of species could be due to ecological speciation in these lineages. Agromyzid flies exhibit patterns of repeated host‐associated radiations. We investigated whether host‐associated population divergence and evidence of divergent selection exist in the leaf minerPhytomyza glabricolaon its sympatric host plants, the holly species,Ilex coriaceaandI. glabra. UsingAFLPs and nuclear sequence data, we found substantial genetic divergence between host‐associated populations of these flies throughout their geographic range. Genome scans using theAFLPdata identified 13 loci under divergent selection, consistent with processes of ecological speciation.EF‐1αdata suggest that I. glabrais the original host ofP. glabricolaand thatI. coriaceais the novel host, but theAFLPdata are ambiguous with regard to directionality of the host shift.

     
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