Attraction to and Oviposition of Monochamus alternatus Adults on Healthy Pinus densiflora to which a Sheaf of Cut Pine Branches was Attached

Abstract

To clarify whether adult Monochamus alternatus, the vector of pine wilt disease, are attracted to slight damage to branches of the host tree, a sheaf of fresh or dead cut branches were attached to four healthy Pinus densiflora in late June 2017, and egg-laying scars and feeding wounds on the stems and branches of the trees caused by the beetles were counted. Egg-laying scars and feeding wounds were found first on all of the trees in mid-July, and their numbers increased until mid-September. The final number of egg-laying scars ranged from 26 to 101 per tree and that of feeding wounds from 10 to 27, while there were no egg-laying scars on the stems of 10 healthy control trees without cut branches. Two of the four trees with cut branches died showing symptoms of pine wilt disease. These results suggest that that cut branches attracted the beetles and caused them to oviposit on healthy host trees. Therefore, slight damage to host trees, such as recently broken branches caused by snowfall or wind, can attract adult M. alternatus and influence their occurrence and expansion, as seen in the historical effects of diseased trees with pine wilt disease.