Interactions between the scelionid egg parasitoid Tiphodytes gerriphagus (Hymenoptera) and its gerrid hosts (Heteroptera)

Tiphodytes gerriphagus parasitized eggs of five Gerris and two Limnoporus species in the laboratory and the parasitoids were reared from field-collected eggs of G. buenoi, G. comatus, G. pingreensis, L. dissortis, and L. notabilis. Eggs of G. buenoi and L. dissortis were parasitized over about 80% of development. Wasps preferred eggs of G. buenoi over those of L. dissortis, which were larger but covered by a jelly coat. However, under field conditions, eggs of L. dissortis laid at the water surface were parasitized more than submersed eggs of Gerris species. Host size (= species) had no apparent effect on adult life-span but affected the body length of adult parasitoids. Size of females was affected more than that of males and lifetime fecudity also varied with host size. Parasitoids laid most of their eggs during the first 4 days after emergence, averaging 8–11 parasitized hosts per day. Tiphodytes gerriphagus was reared from eggs of Limnoporus collected throughout western Canada. Rates of parasitism peaked just after egg production by L. dissortis, suggesting selection for early oviposition by gerrids. Most Limnoporus populations were heavily parasitized by late summer, but in some temporary or newly created habitats, rates of parasitism were lower. Growth of the parasitoid population at a new habitat was slower than at nearby ponds with large resident wasp and gerrid populations, and the lower parasitoid abundance was associated with greater production of L. dissortis. Adults of T. gerriphagus appear to overwinter in gerrid eggs at the bottom of ponds. At temporary sites, wasps may fail to survive the winter and recolonize more slowly than Limnoporus. Interaction with parasitoids may explain the patchy nature of L. dissortis distribution and its restriction to temporary habitats. Presence of T. gerriphagus may also affect the outcome of competitive interactions among gerrid species.