Factors for the Decreased Concentration of MITC Gas in Fumigation Treatments of Pine Logs to Eradicate Monochamus alternatus Larvae

Abstract

In the fumigation treatment of infested pine logs to eradicate Monochamus alternatus larvae, it is necessary to maintain a steady MITC gas concentration in the coverings during the fumigation period. Factors, such as incomplete coverings would decrease the gas concentrations in the coverings and affect mortalities of the insect larvae in the treated logs. In this study, we set several treatments where the logs were sealed with different covering methods in fall and winter and investigated the temporal changes in inner-covering concentrations during the fumigation and larval mortalities in the treated logs. Spot-pouring treatment of the fumigant, instead of spattering it on the logs, was included in the winter series. The temporal changes in the gas concentrations in the fall series showed a similar trend in the complete wrapping and top covering methods, including those with loose coverings. The concentrations under winter conditions were lower than those under fall conditions and further decreased in treatments with loose coverings in the top covering methods. An exceptionally low concentration was recorded in the spot-pouring treatment of the top covering method with standard covering. Larval mortalities were not affected by the decreases in the concentrations. Nevertheless, we must avoid factors causing the decrease in the MITC gas concentrations, such as loose coverings and/or spot-pouring of the fumigant under low-temperature conditions, to secure a high level of insect mortality.