Insecticide resistance is frequently associated with reduced fitness. Reproductive output is a primary component of fitness and, thus, fitness costs associated with reproduction are likely to influence the evolution of resistance. Pink bollworm, Pectinophora gossypiella (Saunders), is a serious pest of cotton and is controlled by transgenic cotton plants that produce Bacillus thuringiensis (Bt) toxins. Here, reproductive fitness costs were examined using pink bollworm males from two independently derived strains resistant to Bt cotton, and susceptible females from an unrelated strain. In a non-competitive environment, resistant and susceptible males had comparable fitness as measured by egg hatching success, female fecundity and mating frequency. In a competitive environment, where resistant and susceptible males competed for a single susceptible female, males from one resistant strain had fewer matings with virgin females than did their susceptible counterparts, but this was not the case in the other resistant strain. Resistant males from both strains, however, suffered reduced sperm precedence, siring 38.6% fewer offspring than susceptible males when they mated first. Resistance to Bt is associated with mutations in a cadherin gene. The large paternity cost seen here is suggestive of a role of cadherin in sperm competition, and provides additional evidence that large fitness costs are associated with resistance to Bt cotton in pink bollworm.
Species 1: Lepidoptera Gelechiidae Pectinophora gossypiella (pink bollworm)
Keywords: insecticide resistance, fitness costs
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