Coexistence of the Two Closely Related Species of Cabbage Stink Bug, Eurydema rugosum and E.pulchrum(Heteroptera:Pentatomidae), in the Field in Central Japan. : I.Distribution, Life Cycle and Host Plant Preferences of the Two Species

Coexistence of the two closely related species, Eurydema rugosum and E. pulchrum was studied both in the laboratory and in the field at Takato in Ina district, Nagano Prefecture, Central Japan. We investigated the distribution, life cycle, seasonal changes of adult population size, host plant preferences, and the effects of host plants on the survival and development of nymphs of the two species. Eurydema rugosum was distributed widely, whereas E. pulchrum was distributed locally in mountainous areas. Therefore, coexistence of the two species generally occurred in the Ina district which has a mountainous terrain. Adult populations of E. rugosum were highest in early or mid-May and decreased gradually thereafter. On the other hand, those of E. pulchrum increased from early July or late August, and the latter out-numbered the former in the autumn. We estimated that E. rugosum had two generations, whereas E. pulchrum had three. No appreciable difference in host plant preferences was found between the two species : the nymphs and the adults of both species fed together on the same host plant throughout the season. In addition, no appreciable difference in the survival and development of the nymphs on different host plants was found between the two species.