Are fitness costs associated with insecticide resistance? A meta-analysis

Insecticide resistance threatens control of agricultural and medically important insect pests. Resistance may come at a fitness cost to the insect pest, and whether these fitness costs exist may determine the persistence of resistance in the absence of insecticides. Not all resistant populations have shown fitness costs associated with resistance. Revealing possible patterns in the effects of insecticide resistance on fitness costs among insecticide classes, resistance levels, and insect orders would improve our understanding of evolutionary costs of resistance and may assist in optimizing existing resistance management strategies. We performed a comprehensive literature search to identify studies that examined fitness costs associated with insecticide resistance. Fitness data were collected on various life-history traits and subjected to multiple meta-analyses to determine overall effects of resistance. Generally, insecticide resistance often came with a cost to fitness; however, there were insecticide classes, orders of insects, and resistance magnitude levels that did not confer a fitness cost. The emerging patterns suggest that (i) resistant female insects exhibited a lower fecundity compared to susceptible females within the orders Diptera, Hemiptera, and Lepidoptera; (ii) resistant juvenile insects had prolonged development compared to susceptible juveniles within the orders Diptera, Hemiptera, and Lepidoptera; (iii) juvenile survival rate was much higher for susceptible than resistant individuals in the orders Lepidoptera, Diptera, and Hemiptera; (iv) female and male adult longevity were reduced for insecticide resistant individuals in the order Diptera, and (v) there was no clear and consistent trend between the magnitude of resistance and potential effects on fitness.