Population dynamics of a thistle-feeding lady beetle Epilachna niponica (Coccinellidae : Epilachninae) in Kanazawa, Japan. 1. Adult demographic traits and population stability

摘要

Population dynamics of a thistle-feeding univoltine lady beetle, Epilachna niponica Lewis (Coleoptera: Coccinellidae), was studied from 1996 to 1999 in Yuwaku, Kanazawa, Japan. The lady beetles often reached such a high density level that food was depleted. The Jolly-Seber method was used for adult marking, release, and recapture data to estimate population parameters of adult number, daily resident rate, longevity, reproductive rate (R, the number of new adults produced per overwintered adults), and survival rate of new adults to the reproductive seasons (S-w). These estimates were compared with those of the Asiu, Kutsuki (A and F), and Kyoto populations, which were previously studied with similar methods and have similar intensities. Asiu and Kutsuki F populations remained at a rather low density with a low R, while Kutsuki A and Kyoto populations reached a high density where food depletion occurred with a high R value. The Yuwaku population often reached a food-depleting level as in the Kutsuki A and Kyoto populations. It also shared the short life span of overwintered adults (13.5 days) of other high-density populations: however. it showed much shorter longevity of new adults (36.6 days), much lower R (1.0-2.5), and higher S-w(43%-53%). In some traits the Yuwaku population was similar to the Asiu population: low R, high S-w, and low population variability (SD of log densities; 0.103 and 0.115 for overwintered and new adults, respectively. which were lowest among the populations).