Seasonal abundance of Ooencyrtus nezarae ISHII (Hymenoptera: Encyrtidae), an egg parasitoid of phytophagous bugs, in summer soybean fields

Abstract

Seasonal fluctuations in the percentage parasitism of phytophagous bug eggs by Ooencyrtus nezarae ISHII and the adult abundance of this parasitoid were investigated in summer soybean fields of Kumamoto, Japan, in 1990 and 1991. O. nezarae parasitized the eggs of four phytophagous bugs, Riptortus clavatus (THUNBERG), Piezodorus hybneri (GMELIN), Eysarcoris guttiger (THUNBERG) and Nezara antennata SCOTT, occurring as a gregarious parasitoid only in eggs of R. clavatus. Among these hosts, R. clavatus eggs were the most important host resource for O. nezarae in summer soybean fields. Parasitism of R. clavatus eggs by O. nezarae was high in both years, and these host eggs had a high value as a resource due to their high density and gregarious parasitism. Only females of O. nezarae were caught by a sticky-suction trap before host oviposition and from the beginning of the host opposition to the emergence of this parasitoid in soybean fields, indicating that only females colonize soybean fields. These colonizing females increased with increasing egg density of R. clavatus. The sex ratio of emerging O. nezarae adults became male-biased suggesting that females disperse more readily from emergence sites than males.