WHAT CHANGED THE DEMOGRAPHY OF AN INTRODUCED POPULATION OF AN HERBIVOROUS LADY BEETLE

1. The population dynamics of an introduced population of Epilachna ni ponica (Lewis) (Coleoptera: Coccinellidae) was investigated for a 7-ye ar period following its introduction to a site outside of its natural range. A population from Asiu Experimental Forest was introduced to Ky oto University Botanical Garden, 10 km south of its natural distributi on. 2. Arthropod predation was much lower in the introduced than in th e source population. As a result of the lower predation in the Botanic al Garden, larvae reached densities five times higher than in the Asiu Forest and host plants were frequently defoliated. Food shortage caus ed larval deaths from starvation and increased dispersal. 3. The densi ty of the introduced population was much more variable than that of th e source population. The variation in population density in both the i ntroduced and source populations is limited by density-dependent reduc tion in fecundity and female survival. However, variation in the intro duced population's density was increased due to host plant defoliation that resulted in overcompensating density-dependent mortality. In yea rs with high larval density plants were defoliated and this increased adult mortality during the prehibernation period. Besides, the density -dependent regulatory mechanisms that produce population stability wer e weaker in the introduced population than in the source population.