Volatile Essential Oils Can Be Used to Improve the Efficacy of Heat Treatments Targeting the Western Drywood Termite: Evidence from a Laboratory Study

Essential Oils in Urban Insect Management-A Review

The allures of city life have culminated in the rise of urban populations resulting in conditions that promote the establishment of certain insect pests. Globally, the public health significance of these urban insect pests is enormous, ranging from billions of dollars to loss of lives. Most chemical insecticides no longer provide the anticipated level of control, and significant insecticide resistance has been reported. Therefore, there has been a spike in interest for alternatives to conventional insecticides. Among them, natural products from plants such as essential oils (EOs) and essential oil components (EOCs) have enjoyed the most attention owing to widespread reports of efficacy and toxicity even against insecticide-resistant urban insects. Yet, there is no comprehensive synthesis on the extent and impact of the management of urban insects using EOs or EOCs. Such a review is highly relevant since it provides a means to assess the extent of progress made, shortfalls, limitations, and prospects. More so, we hope it can be used to make informed decisions and develop relevant policies reliably. We present the ranges of insecticidal effects of EOs, EOCs, and commercially available EO-based products from laboratory and field studies. Finally, we discuss the gaps in our knowledge and prospects for the sustainable use of EOs.

Field Demonstration of Heat Technology to Mitigate Heat Sinks for Drywood Termite (Blattodea: Kalotermitidae) Management

Simple Summary

The West Indian drywood termite, Cryptotermes brevis poses a significant economic threat in Hawaii, the southeast portion of continental United States, and throughout tropical and subtropical regions worldwide. Heat treatment is among the nonchemical options to manage them. A typical heat treatment may not be able to provide a complete kill of drywood termites due to the presence of difficult-to-heat areas. To mitigate this effect, studies were conducted in drywood termite-infested condominiums in Honolulu, Hawaii, where either a standard heat treatment performed by a heat remediation company or improved heat treatment methods were used. For improved treatments, heated air was directed into the drilled bases of infested cabinets for better heat penetration. Eight temperature sensors showed that sufficiently high heat was recorded at difficult-to-heat areas, including inside thick wooden cubes, for 120 min, with target temperatures of above 46 °C or 50 °C capable of killing drywood termites. A pre-treatment and a 6-month posttreatment inspection were performed to monitor termite inactivity using visual observations and by recording the numbers of spiked peaks on a termite detection device. The data showed no termite activity in improved heat treatment condominiums at 6-month posttreatment. Guidelines for the improved heat treatment are proposed.

Abstract

With heat treatments to control drywood termites (Blattodea: Kalotermitidae), the presence of heat sinks causes heat to be distributed unevenly throughout the treatment areas. Drywood termites may move to galleries in heat sink areas to avoid exposure to lethal temperatures. Our studies were conducted in Crytotermes brevis-infested condominiums in Honolulu, Hawaii to reflect real-world condominium scenarios; either a standard heat treatment performed by a heat remediation company, or an improved heat treatment was used. For improved treatments, heated air was directed into the toe-kick voids of C. brevis infested cabinets to reduce heat sink effects and increase heat penetration into these difficult-to-heat areas. Eight thermistor sensors placed inside the toe-kick voids, treatment zone, embedded inside cabinets’ sidewalls, and in a wooden cube recorded target temperatures of above 46 °C or 50 °C for 120 min. Pre-treatment and follow-up inspections were performed at 6 months posttreatment to monitor termite inactivity using visual observations and by recording the numbers of spiked peaks on a microwave technology termite detection device (Termatrac). In improved treatment condominiums, significantly higher numbers of spiked peaks were recorded at pre-treatment as compared to 6 months posttreatment. Efficacious heat treatment protocols using the improved methods are proposed.

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

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.