Fitness cost of imidacloprid resistance in generalist predator from northernmost and equatorial range in the tropics

Life-history traits and population size of organisms may be affected by fitness costs associated with insecticide resistance. In this study, we examined the insecticide resistance and life-history traits of Paederus fuscipes (Curtis), a common generalist predator, in field populations from Taiwan (high-latitude region; 22° N–25° N) and Malaysia (low-latitude region; 3° N–5° N). The results showed that Malaysian populations had higher imidacloprid resistance compared with Taiwanese populations. The fitness costs associated with imidacloprid resistance resulted in reduced fecundity, longer adult pre-oviposition period, shorter egg length, and lighter pupal weight in the Malaysian populations, in contrast to the Taiwanese populations. However, the immature developmental time of the Malaysian populations was relatively short compared with the Taiwanese populations. The longevity of the Taiwanese populations was significantly shorter compared with the Malaysian populations. The fecundity of the adult populations increased in inverse proportion to longevity. The intrinsic rate of increase was significantly lower in the Malaysian populations compared with the Taiwanese populations. This regional-scale study provided insights into the differences in life-history traits and population growth of P. fuscipes as a result of fitness cost. However, it is worth noting that despite the high intrinsic rate of increase observed in the Taiwanese populations, among other factors, cannibalism may serve as a density-dependent compensatory mechanism in regulating population size.