Sex ratio distorters and resistance management

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Sex ratio distorting agents are widespread in the arthropods, with both endosymbiont microorganisms and selfish genetic elements causing female biased sex ratios in many species. The presence of these agents is likely to cause changes to the adaptive capacity of the affected populations, with potential effects on both the rate of evolution and the stability of biocide (chemical pesticides, biocontrol agents) resistance being the most important applied consequence of sex ratio distortion. These ideas have never been tested experimentally and have hardly been addressed by theoreticians either. We propose to test the potential effects of the presence of sex ratio distorters using laboratory experimental evolution experiments. Both the effects of selfish genetic elements, in Drosophila pseudoobscura, and endosymbionts, in D. melanogaster, will be tested by experimentally selecting for resistance to the pyrethroid pesticide permethrin, and the rate at which the populations become resistant will be compared with controls with no sex ratio distorters. The rate of loss of resistance in populations where selection has been relaxed will also be tested.

Based on the results from the laboratory experiments, we will construct mathematical models of resistance evolution in pest populations and use these to examine resistance evolution and management in three scenarios: pests with sex ratio distorters present, pests which experience the introduction of a sex ratio distorter and pests which evolve suppression of a sex ratio distorter. This will produce a theoretical framework for the assessment of the potential impact of sex ratio distorters in practical pest management and also allow us to assess the potential benefits of introducing sex ratio distorters to pest populations in order to aid in resistance management.