Volatile Essential Oils Can Be Used to Improve the Efficacy of Heat Treatments Targeting the Western Drywood Termite: Evidence from Simulated Whole House Heat Treatment Trials

Abstract

Colonies of western drywood termites, Incisitermes minor (Hagen) (Blattodea: Kalotermitidae), are difficult to detect and treat due to their cryptic nature. The use of heated air to create lethal temperatures within infested wood serves as a nonchemical treatment option targeting whole structure or large portions of the structure. However, the presence of hard-to-heat areas and potential risk of damage for heat-sensitive items are recognized as important challenges. Here, we tested if a localized injection of volatile essential oil could be utilized to address the heat sink issue, potentially increasing the overall efficiency of heat treatments against drywood termites. Artificially infested wooden blocks were placed in several locations of the test building, and heat treatments were conducted. For the treatment group, a small amount of essential oil (methyl salicylate) was added in the blocks prior to the heat treatment. All blocks placed in uninsulated wall voids had 92-100% termite mortality by day 7. However, the presence of a large concrete wall in the subarea hindered heating of blocks therein, resulting 36-44% mortality by day 7 when there was no essential oil treatment. Incorporation of the essential oil substantially increased the control efficacy for the subarea, resulting in more than 90% mortality. This approach might also be helpful in reducing the risk of potential heat damage during heat treatment without compromising its control efficacy.