Seasonal Emergence and Flight Behavior of the Oak Ambrosia Beetle Platypus quercivorus along an Altitudinal Gradient in the High Elevation Areas

Abstract

Japanese oak wilt usually occurs at altitudes under 300 m. However, it is reported to occur above 1,000 m in Toyama Prefecture, Japan, suggesting that this disease could expand to higher elevations. Ecological knowledge of the occurrence of Platypus quercivorus, which is an ambrosia beetle vector of Japanese oak wilt, at high elevations is important for the prediction and prevention of the expansion of this disease. Therefore, this study investigated the seasonal occurrence and flight behavior of P. quercivorus adults along an altitudinal gradient in the Tanigawa Mountains, which lie on the boundary between Gunma and Niigata Prefectures. To capture P. quercivorus adults emerging from bore holes, emergence traps were set on host oak trees (Quercus crispula) that had died in the last year at every 100 m altitude along a gradient of increasing altitudes (600–1,000 m). Additionally, flight interception traps were set in the same manner to capture flying P. quercivorus adults. Our results showed significant decreases in the number of emerging adults per bore and flying adults at higher altitudes. In conclusion, the reproductive success of P. quercivorus at higher altitudes above 600 m was considerably more reduced than that of lower ones; such a decrease at altitudes over 900 m might be caused by a decrease in the number of Q. crispula trees as a result of change in tree species composition.