Factors Responsible for Survival of Monochamus alternatus in the Fumigation-treated Pine Logs

Abstract

In the fumigation treatment of infested pine logs to eradicate Monochamus alternatus larvae, decreased MITC gas concentration resulting from insufficient application of the fumigant and/or other factors would reduce insect mortalities in the logs. Close contact of the wood surface with a masking object such as the ground can also negatively impact the insecticidal effect by preventing infiltration of the effective chemical into the logs. In this study, we prepared log-piles, and set a test log to investigate insect mortality at the middle of each pile. We also set two logs at the bottom and top of the pile to make them contact with the ground and the covering sheet, respectively. Then the log-piles were fumigated by one of the following three types of covering methods: complete wrapping, top covering, and top covering with spot-pouring of the fumigant. We detected living insects in the test logs taken from a log-pile with complete wrapping and three log-piles with top covering with spot-pouring, and the maximum MITC gas concentration in these coverings was ≤2.14 g/m³ for those piles. The living insects were likely to occur in the logs that were in contact with the ground or the covering sheet, and could grow into adults. To achieve a high level of insect mortality, we need to avoid factors causing the decrease in MITC gas concentrations, such as spot-pouring of the fumigant and close contact of the logs with the ground and covering sheet.