Linking parasitoid nectar feeding and dispersal in conservation biological control

The nectar provision hypothesis posits that biological control by parasitoids can be enhanced by providing supplemental nectar in the vicinity of cropland. The rationale for this hypothesis is that parasitoid longevity and fecundity can be greatly enhanced by sugar meals and that many agricultural areas are devoid of naturally occurring sugar sources. While some experimental field studies have produced results supporting the nectar provision hypotheses, many others have failed to show that supplemental nectar can improve biological control by parasitoids. I propose that some parasitoids may engage in medium- or long-range dispersal upon feeding on nectar and thus not contribute to local parasitism adjacent to flower plantings. If true, this could help to explain some of the negative results of nectar supplementation experiments. I further propose that certain conditions favor nectar-induced dispersal and discuss four of these here: (i) the risk of self-superparasitism, (ii) the risk of density-dependent hyperparasitism, (iii) benefits of 'spreading the risk’ of catastrophic mortality and (iv) the risk of inbreeding among parasitoid offspring.