Egg parasitoids of phytophagous bugs in soybean: Mobile natural enemies as naturally occurring biological control agents of mobile pests

Egg parasitism of mobile phytophagous bugs in two soybean fields was analyzed to address the question: what characteristics do their egg parasitoids have as naturally occurring biologically effective control agents? Eggs of four bug species, Piezodorus hybneri (Gmelin), Eysarcoris guttiger (Thunberg), Riptortus clavatus (Thunherg), and Megacopta punctatissimum (Montandon) were found. Ooencyrtus nezarae Ishii parasitized eggs of all four bug species, while Telenomus triptus Nixon parasitized eggs of only P. hybneri and E. guttiger. Gryon nigricorne (Dodd) and Gryon japonicum (Ashmead) were specific to R. clavatus. Only Paratelenomus minor (Watanabe) emerged from M. punctatissimum eggs. Percentage parasitism by each of the two nonspecific parasitoids often was higher than percentage parasitism by each of the three host-specific parasitoids. O. nezarae was a good colonizer in soybean fields, synchronizing female colonization with the appearance of its host. Although a high level of parasitism by O. nezarae occurred during the first half of a host infestation period, part of the emerging O. nezarae females dispersed from fields while their hosts continued to oviposit. This behavior resulted in a failure of O. nezarae to increase parasitism of its host during the latter half of its reproductive period. Female dispersal of this polyphagous parasitoid is a strategy for exploiting its mobile hosts, and the degree of its dispersal is correlated with its colonizing ability. It is suggested that polyphagy and high dispersal ability are the main characteristics of effective natural enemies of naturally occurring mobile pests.