Insecticide resistance mutations are widely assumed to carry fitness costs. However studies to measure such costs are rarely performed on genetically related strains and are often only done in the laboratory. Theory also suggests that once evolved the cost of resistance can be offset by the evolution of fitness modifiers. But for insecticide resistance only one such example is well documented. Here we critically examine the literature on fitness costs in the absence of pesticide and ask if our knowledge of molecular biology has helped us predict the costs associated with different resistance mechanisms. We find that resistance alleles can arise from pre-existing polymorphisms and resistance associated variation can also be maintained by sexual antagonism. We describe novel mechanisms whereby both resistant and susceptible alleles can be maintained in permanent heterozygosis and discuss the likely consequences for fitness both in the presence and absence of pesticide. Taken together these findings suggest that we cannot assume that resistance always appears de novo and that our assumptions about the associated fitness costs need to be informed by a deeper understanding of the underlying molecular biology.

广泛认为杀虫剂抗性突变会带来健身成本。然而，测量此类成本的研究很少在遗传相关菌株上进行，并且通常仅在实验室中进行。理论还表明，一旦进化，抵抗力的成本就可以通过适应性调节剂的发展来抵消。但是对于杀虫剂的抗药性，只有一个这样的例子得到了充分的证明。在这里，我们认真地研究了在没有农药的情况下有关健身成本的文献，并询问我们的分子生物学知识是否有助于我们预测与不同抗药性机制相关的成本。我们发现，抗性等位基因可能来自先前存在的多态性，并且与抗性相关的变异也可以通过性拮抗作用得以维持。我们描述了新的机制，从而可以在永久性杂合中维持抗药性和易感性等位基因的存在，并讨论了在存在和不存在农药的情况下，适应性的可能后果。综上所述，这些发现表明我们不能假设总是会出现抵抗从头开始，我们对相关适应性成本的假设需要通过对基础分子生物学的更深入了解来提出。