Nest visitors of Vespula wasps and their potential use for biological control in an invaded range

The common and the German wasp, Vespula vulgaris and V. germanica, have proved to be prolific invasive species capable of degrading local ecosystems and costing invaded countries millions of dollars annually. Despite clear incentive, control strategies are yet to have any significant deleterious impact on invasive populations. Several species of arthropods are known to inhabit Vespula nests and feed upon developing larvae as either parasitoids or predators. Recent control strategies propose the use of such parasitoids as agents of biocontrol against invasive wasps (Volucella inanis in particular). Despite a general understanding of parasitoid ecology, some aspects such as prevalence, distribution, and behaviour remain limited. Here, we surveyed natural enemy prevalence in wasp nests over the period of three years and we tested larvae prey preference of two Volucella species, V. inanis and V. zonaria towards Vespula wasps. We find V. inanis to be the most prevalent of four prominent candidates for Vespid biocontrol-V. inanis, V. zonaria, Sphecophaga vesparum, and Metoecus paradoxus. Using two-choice assays, we find larvae of V. inanis to have slight yet significant prey preference for V. vulgaris larvae over V. germanica larvae, whilst V. zonaria display no preference. Furthermore, V. inanis were not averse to still predating upon V. germanica, doing so in 41% of trials. Prior exposure has no effect on the prey-preference. Our work provides experimental evidence that V. inanis is a promising candidate for biocontrol of invasive Vespula wasps, as the larvae predate on both target species of Vespula and display no exclusive preference among them.