How to Break into a Microcosm: Localization of Hidden Hosts by Fig Wasp Parasitoids

Abstract

Host-finding behaviour and decision-making in a tri-trophic interaction are often complex, especially when hosts are hidden within plant or animal tissues. We study how parasitoid fig wasps assess fig hosts for ovi-position. These wasps oviposit into fig inflorescences (syconia) in which conspecifics have previously depo-sited eggs, possibly to avoid sib-mating for offspring that will develop and mate within these enclosed inflo-rescences. The syconia previously visited by conspecif-ics can be identified from species-specific chemical footprints left on the outer syconium surface, and these are chemically characterized. The tarsal mor-phology that may facilitate such identification is also described. Fig wasps have a haplodiploid breeding system in which males are haploid, developing from unfertilized eggs, and are much smaller in size than females. We therefore also experimentally determined that these parasitoids do not deposit fertilized eggs destined to become females on male hosts, a behaviour likely driven by the greater nutritional requirements of female offspring compared to the smaller-sized males. We also quantified carbon dioxide (CO2) pro-duction from galls of different species, as species-specific hosts within the syconia are likely identified by differential CO2 production from galls, whose le-vels are assessed via the sensilla present on the parasi-toid ovipositor.