Haplodiploidy, sex, and the evolution of pesticide resistance

The assumption that males and females are equally tolerant to pesticides in haplodiploid arthropods led to the prediction that the evolution of resistance is faster in haplodiploid than in diploid arthropods. However, in this review, it was found that the ratio of male to female tolerance is substantially smaller in haplodiploid than in diploid arthropods, indicating that resistance alleles are not strongly up-regulated in haploid males. In addition, males were generally less tolerant than females in both haplodiploid and diploid arthropods. Factors such as sexual size dimorphism and sex-dependent selection may account for the lower tolerance in males than in females. Little among-population variation in the ratio of male to female tolerance was found in three species. Moreover, the tolerance ratio generally remained unchanged by selection for resistance to pesticides, although significant among-species variation was present within arthropod orders. This indicates that sexual dimorphism in pesticide tolerance evolves at a slower rate than resistance to pesticides. Simulations considering between-sex differences in pesticide tolerance showed that resistance evolution can be slower in haplodiploids than in diploids. Recessive resistance, low male tolerance to pesticides, fitness costs expressed in males, and the use of refuges contributed in substantially delaying the evolution of resistance in haplodiploid arthropods. These findings cast a new perspective on the evolution of pesticide resistance in haplodiploid herbivores and natural enemies.