History Matters: Oviposition Resource Acceptance in an Exploiter of a Nursery Pollination Mutualism

In the fig-fig wasp nursery pollination system, parasitic wasps, such as gallers and parasitoids that oviposit from the exterior into the fig syconium (globular, enclosed inflorescence) are expected to use a variety of chemical cues for successful location of their hidden hosts. Behavioral assays were performed with freshly eclosed naive galler wasps. Syconia with different oviposition histories, i.e. with or without prior oviposition, were presented to wasps in no-choice assays and the time taken to the first oviposition attempt was recorded. The wasps exhibited a preference for syconia previously exposed to conspecifics for oviposition over unexposed syconia. Additionally, syconia exposed to oviposition by heterospecific wasps were also preferred for oviposition over unexposed syconia indicating that wasps recognise and respond to interspecific cues. Wasps also aggregated for oviposition on syconia previously exposed to oviposition by conspecifics. We investigated chemical cues that wasps may employ in accepting an oviposition resource by analyzing syconial volatile profiles, chemical footprints left by wasps on syconia, and syconial surface hydrocarbons. The volatile profile of a syconium is influenced by the identity of wasps developing within and may be used to identify suitable host syconia at long range whereas close range preference seems to exploit wasp footprints that alter syconium surface hydrocarbon profiles. These cues act as indicators of the oviposition history of the syconium, thereby helping wasps in their oviposition decisions.