A shift toward early reproduction in an introduced herbivorous ladybird

1. In May 1971, fifteen male and thirty female overwintering adults of a thistle-feeding ladybird Epilachna niponica were taken from the Asiu Experimental Forest of Kyoto University and introduced into the Botanical Garden of Kyoto University, 30 km south of Asiu and 10 km south of the southern limits of its distribution. The introduced population established successfully and thereafter maintained densities sufficiently high to defoliate their host plants.
2. Reproductive parameters (reproductive lifespan of females, overall fecundity, and oviposition schedules) of the introduced population were compared with those of the source population 10 years after the introduction. Comparisons were made in the laboratory under five temperature regimes.
3. The lifespan of females differed significantly with temperature, decreasing linearly with increasing temperature. Temperature also had a significant effect on overall fecundity for both populations; overall fecundity at 15 and 30 °C was significantly lower than that at the 20–25 °C regimes.
4. The oviposition activity of the introduced population was significantly higher than that of the source population at 23 and 25 °C. The lifespan of females of the introduced population was also significantly shorter than those of the source population at 20 and 25 °C.
5. The reduced lifespan and higher oviposition activity of introduced females indicate that they directed greater reproductive efforts early in their reproductive lifetime than those of the source population.