Effect of Environmental Factors on Strepsipteran Parasite Abundance in Vespine Wasps (Hymenoptera: Vespidae)

Abstract

Xenos is a strepsipteran genus parasitizing hornets of the Vespa spp. In Japan, parasitism levels in hornets have been examined for two Xenos species. These studies have indicated that parasitism levels vary with the seasons but are inconsequential compared to other potential factors that reduce the number of host colonies. However, a comprehensive analysis of parasitism levels accounting for various factors such as host species, seasons, and years was not conducted. To address this gap, we conducted a four-year study in which we collected Vespa spp. using bait traps and assessed parasitism levels concerning those factors. Additionally, we evaluated the number of male and female Xenos parasites throughout the seasons. A total of 11,766 wasps from six hornet species were collected, with three of the species conspicuously parasitized by two Xenos parasites: Vespa analis (Fabricius, 1775) parasitized by Xenos oxyodontes (Nakase & Kato, 2013) and Vespa mandarinia (Smith, 1852) and Vespa ducalis (Smith, 1852) parasitized by Xenos moutoni (Buysson, 1903). Levels of parasitism by X. oxyodontes exceeded those by X. moutoni. Seasonal and yearly variations influenced the levels of parasitism by the two Xenos spp. We observed that male and female Xenos parasites emerged simultaneously over 2 – 3 months, suggesting the likelihood of multivoltinism in temperate regions. Our study also examined several key factors influencing the fluctuations in the population size of these parasites.