POPULATION ECOLOGY OF THE AZUKI-BEAN BEETLE, CALLOSOBRUCHUS-CHINENSIS (L), (COLEOPTERA, BRUCHIDAE) ON 2 WILD LEGUMINOUS HOSTS, VIGNA-ANGULARIS VAR NIPPONENSIS AND DUNBARIA-VILLOSA

The population ecology of the azuki bean beetle, Callosobruchus chinensis (L.) was studied on two wild leguminous hosts; annual Vigna angularis (WILLD.) OHWI & OHASHI var. nipponensis (OHWI) OHWI & OHASHI and perennial Dunbaria villosa (THUMB.) MAKINO. Both legumes bloom from mid-August to late September, and produce mature pods from mid-August to late September, and produce mature pods from mid-September to late October. Adult beetles occurred on the colonies of the two wild legumes from mid-August to mid-October. Females laid their eggs on the mature pods of both legumes from mid-September to mid-October. Most active oviposition was in late September. Eggs were deposited contiguously on mature pods, but larval density was less than one per seed. The larval survival rate decreased rapidly until the 1st instar larvae penetrated into pod seeds. After penetration, the survival rate slightly decreased until pod dehiscence. These ecological characteristics were similar to those observed in the cultivated azuki bean, Vigna angularis (WILLD.) OHWI & OHASHI. Percentage of seeds infested by C. chinensis in each colony of D. villosa ranged from 0% to 13.5%. The percentages changed yearly, but were almost always less than 5%.