Effect of aerial spraying of thiacloprid on pine sawyer beetles (Monochamus alternatus) and honey bees (Apis mellifera) in pine forests

Monochamus alternatus is a very important vector of the pine wood nematode (Bursaphelenchus xylophilus) which is the causal agent of pine wilt disease. To reduce population density of M. alternatus, thiacloprid has been sprayed by aircrafts on pine forests. Thus, we examined the effect of aerial spraying as contact toxicity and thiacloprid residues of pine branches as ingestion toxicity on the mortality of M. alternatus in pine forests in Yangsan, Korea. In addition, the effect of aerial spraying on honey bees, Apis mellifera, was tested in the same locality. Thiacloprid was sprayed once a month from June to August in 2016. To test the effect of thiacloprid, eight M. alternatus and ten honey bees were put into each small mesh cage, which were hung on pine trees in each study plot. Thiacloprid appeared to be effective for reducing longevity of M. alternatus, while mortality and abnormal behaviors were not found for honey bees. In addition, longevity of M. alternatus beetles was declined by thiacloprid residues of pine branches compared to the control group. However, we found that dead pine trees infected by pine wood nematodes in the next year similarly occurred in our study area whether thiacloprid‐aerial spraying occurred or not. Consequently, thiacloprid sprayed by aircraft may be an effective control agent for Monochamus beetle adults without negative effect on honey bees, but aerial application to prevent expansion of pine wilt disease should be reassessed.