The cost of parasitism: High larval developmental mortality following attacks by a parasitoid fig wasp on a fig pollinating wasp

Parasitoids contribute to controlling phytophagous insect populations. Their action on a host is often measured by numbers of emerging adult parasitoids. However, parasitoid oviposition attempts may lead to host mortality and sometimes both host and parasitoid die during larval development. Therefore, establishing the effect of parasitoids on host populations requires estimating total effect of parasitoids. The communities of wasps developing in figs (the closed inflorescences of Ficus) have become a model system to investigate micro-hymenopteran interaction networks. A galled ovule produces either a single galling wasp or a single parasitoid providing a simple way to measure costs. However, some galled flowers produce no wasps. We show that about one quarter of galled flowers fail to produce pollinator offspring in the absence of parasitoids. In the presence of parasitoids, the number of empty galls is increased. For each emerging parasitoid, 1.9 pollinator larvae were killed. Hence, host mortality induced by parasitoids is much larger than actual parasitoid production, a feature documented in some other host-parasitoid interactions and that may be pervasive in nature.