Volatile emissions from an epiphytic fungus are semiochemicals for eusocial wasps

Background/Question/Methods

Microbes are ubiquitous inhabitants of plant surfaces. However, interactions between epiphytic microbes and arthropods are rarely considered to be a factor that mediates arthropod behaviors. Here we report evidence for a functional symbiosis between a widely distributed epiphytic fungus and two eusocial hymenopterans. We tested the hypothesis that volatiles emitted by an epiphytic fungus act as wasp semiochemicals. We isolated the fungus Aureobasidium pullalans from apple pomes and quantified volatile compounds emitted by fungal colonies. We tested the attractiveness of fungal colonies and fungal volatiles to social wasps (Vespula spp.) in the field.

Results/Conclusions

Three important findings emerged: 1) traps baited with A. pullalans caught 2750% more wasps on average than unbaited control traps; 2) the major headspace volatiles emitted by A. pullalans were 2-methyl-1-butanol, 3-methyl-1-butanol, and 2-phenylethyl alcohol; and 3) a synthetic blend of fungal volatile compounds attracted 4933% more wasps on average than unbaited controls. Wasps were most attracted to the volatile 2-methyl-1-butanol. The primary wasp species attracted to fungal volatiles were the western yellowjacket (Vespula pensylvanica) and the German yellowjacket (V. germanica), and we found both species externally vectoring A. pullalans. This is the first experimental evidence that eusocial wasps orient to microbial volatile emissions, and our experiments indicate that volatile compounds emitted by an epiphytic fungus can be responsible for wasp attraction. Our work implicates epiphytic microbes as important components in the community ecology of some eusocial hymenopterans, and we suggest that fungal emissions may signal suitable nutrient sources to foraging wasps.