Smaller nests of the hornet Vespa analis (Hymenoptera, Vespidae) are more severely affected by the strepsipteran parasite Xenos moutoni (Strepsiptera, Stylopidae) than are larger nests

The parasite Xenos moutoni inactivates workers and castrates reproductives of the Japanese hornet Vespa analis. Using over 500 nests, we investigated the relationship between hornet nest size (number of cells) and the proportion of parasitized adults (i.e., prevalence) in central Japan. Over 3 years, 36–48% of nests had more than one parasitized adult, and approximately 3–5% of female adults (mostly workers) and 1–3% of male adults were parasitized within the population. The number of cells did not differ between nests with and without parasitized workers; therefore, the effects of parasite-caused losses within the worker force on nest size appear to be negligible. However, the prevalence of parasitized workers tended to decrease with an increase in the number of cells. Our analysis indicated that the number of parasitized workers was consistently low and did not increase with nest size, resulting in a relatively high prevalence in small nests.