Intrinsic competition among solitary and gregarious endoparasitoid wasps and the phenomenon of ‘resource sharing’

1. Intrinsic competition was compared in three species of braconid wasps, the solitary Meteorus pulchricornis Wesmael, and the gregarious Cotesia kariyai (Watanabe) and Cotesia ruficrus Haliday in caterpillars of their common host, the armyworm Mythimna separata Walker. Competition was determined in pair‐wise contests consisting of simultaneous and subsequent parasitisms at various time intervals between the first and second attacks (<1, 24, 48, 72, and 96 h). 2. The experiment revealed that the solitary M. pulchricornis parasitoid was generally superior over the other two gregarious Cotesia species, although, in some cases C. kariyai out‐competed M. pulchricornis when ovipositing first. In contrast, irrespective of the time interval between parasitism and multiparasitism, C. ruficrus always lost in competition with M. pulchricornis . 3. Remarkably, both C. kariyai and C. ruficrus occasionally emerged from the same multiparasitised caterpillar when the time interval between the first and second attacks was small. However, cumulative brood sizes of both species were generally less than when C. kariyai and C. ruficrus developed alone, suggesting that some competition did occur between these two species. 4. Inter‐specific ‘resource sharing’ amongst parasitoid larvae has rarely been described in the literature. In the present study, the conditions in which ‘resource sharing’ in parasitoids can evolve are discussed. Further, we describe differing host usage strategies in parasitoids and how these can affect the outcome of aggressive larval competition.