Yearly and seasonal changes in species composition of hornets (Hymenoptera: Vespidae) caught with bait traps on the Sea of Japan coast

Hornets belong to the genus of Vespa, and are potentially effective predators of insect pests in forests and other environments. To assess the potential impact of prey foraging by the Vespa species, studies have attempted to understand species composition of hornets caught with bait traps in several regions in Japan. These studies showed that the species composition of hornets was different among the different regions in Japan, possibly due to the differences in the geographical distribution and climates. Additionally, the species composition of hornets has only been examined in the inland regions of Japan. In this study, we studied species composition of hornets caught with bait traps in Niigata city on the coast of the Sea of Japan, for a period of four years. The species composition observed in Niigata city was very similar to the composition seen in other temperate, warmer regions, but diffe¬rent from that in subarctic and heavy snowfall regions. There was a single peak in the trap catch due to seasonal changes in the two major species, V. analis and V. ducalis. There were also yearly changes in the species composition of hornets in Niigata city. The possible causes of the differences among the hornet populations in the seasons and years are discussed in this study.