Seasonal Variation in a Hymenopterous Parasitoid, Holcotetrastichus rhosaces (Walker) (Hymenoptera: Tetrastichinae), on Its Hosts, Cassida nebulosa L. and C. piperata Hope (Coleoptera: Chrysomelidae), in Sendai, Northeastern Area of Japan

摘要

To investigate the seasonal variation of parasitism on Cassida nebulosa L. and C. piperata Hope, this research was conducted at the experimental field of Tohoku University in Sendai, Japan, where these tortoise beetles were parasitized by hymenopterous parasitoid Holcotetrastichus rhosaces (Walker). Percentage parasitism started to increase from the middle of July and reached nearly 100% in August. Adults of H. rhosaces emerged from the pre-pupae of the tortoise beetles, with 6 to 30 adults emerging per pre-pupae. The second generation of C. nebulosa and C. piperata was heavily parasitized by H. rhosaces. The adults of these tortoise beetles were rarely found in the field during late summer due to the high rates of parasitism.