Effects of host size on the sex ratio, clutch size, and size of adult Spathius agrili, an ectoparasitoid of emerald ash borer

The idiobiont ectoparasitoid, Spathius agrili Yang (Hymenoptera: Braconidae), parasitizes the concealed larvae of the emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), which feed on the inner bark of ash trees (Fraxinus spp.). The objectives of this study were to investigate the effects of host larval size on parasitoid clutch size, offspring sex allocation, and adult body length. Results showed that the number of parasitoid eggs per host was positively correlated with host size as measured by larval weight, pronotum width, body length, and body width. The percentage of emerging parasitoids that were female was greater when eggs were laid on large larvae. More parasitoid progeny successfully developed on large host larvae, and parasitoid progeny survival was slightly higher than on small host larvae. Survival of parasitoid progeny was positively related to the width of the host gallery. There were significant differences among the body lengths of adult parasitoid offspring that developed on different sizes of host larvae, especially for female wasps. Furthermore, females were typically longer than males developing on the same host.