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 Asi u Experimental Forest of Kyoto University and introduced into the Bota nical 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 sufficien tly high to defoliate their host plants. 2. Reproductive parameters (r eproductive lifespan of females, overall fecundity, and oviposition sc hedules) of the introduced population were compared with those of the source population 10 years after the introduction. Comparisons were ma de in the laboratory under five temperature regimes. 3. The lifespan o f females differed significantly with temperature, decreasing linearly with increasing temperature. Temperature also had a significant effec t on overall fecundity for both populations; overall fecundity at 15 a nd 30 degrees C was significantly lower than that at the 20-25 degrees C regimes. 4. The oviposition activity of the introduced population w as significantly higher than that of the source population at 23 and 2 5 degrees C. The lifespan of females of the introduced population was also significantly shorter than those of the source population at 20 a nd 25 degrees C. 5. The reduced lifespan and higher oviposition activi ty of introduced females indicate that they directed greater reproduct ive efforts early in their reproductive lifetime than those of the sou rce population.