Different trophic positions among social vespid species revealed by stable isotopes

The social vespid wasps are common insect predators and several species behave in unison in the same biotopes. It is commonly accepted that social wasps are mainly opportunistic generalist predators without differences in prey selection and hence they compete for the same food resources. Trophic positions of six vespid wasp species and their potential prey from four sites in Finland and one in the UK were evaluated using carbon and nitrogen stable isotopes (δ(13)C and δ(15)N). The difference in isotope values indicated different trophic positions among species. In general, Dolichovespula spp. showed higher δ(15)N values than Vespula spp., which suggests that Dolichovespula forage on higher trophic levels. Dolichovespula media (Retzius, 1783) showed the highest δ(15)N values, whereas Vespula vulgaris showed the lowest. Dolichovespula media partly expresses apex predator-like δ(15)N values, whereas Vespula species tend to forage on primary consumers. The largest species Vespa crabro (Linnaeus, 1758) showed also similar δ(15)N values as Vespula spp. However, δ(13)C and δ(15)N values of V. vulgaris workers varied slightly during the season. This study offers novel insights about the trophic segregation in the social wasp community, suggesting specialization in diet resource utilization, especially between Dolichovespula and Vespula.