Although a species rarely encountered by Australian pest managers, the West Indian drywood termite is an invasive species that pest managers should be well informed about.
Latest drywood termite research
The economic impact of banning sulfuryl fluoride for drywood termite treatments
Due to its potential role in global warming, there is increasing regulatory pressure to ban the use of sulfuryl fluoride as a fumigant for drywood termite control. As sulfuryl fluoride is the sole remaining fumigant available for the treatment of several structural pests, including drywood termites, researchers have developed an economic framework to assess the impact of banning sulfuryl fluoride to help inform decision makers.1
Looking at the drywood termite market in California alone, the researchers estimated that the transition from a combination of fumigation (whole of house) and local (spot) treatments, which is the makeup of the current market, to a market entirely based on local treatments, would see costs to the public increase by a low estimate of US$1.42 billion (due to increased treatment cost and increased damage) to a high estimate of US$4.31 billion. This effectively puts a cost per ton of carbon dioxide at US$624-1475, should sulfuryl fluoride by banned. This is significantly higher than the price range for carbon dioxide calculated for other industrial applications, which is typically in the range of US$30-150 per ton. As a result, the authors see the banning of sulfuryl fluoride as a suboptimal option, at least until a suitable alternative can be identified. But as the authors also point out, research and innovation to find a suitable alternative are lacking.
Spot Treatment Alternatives for Drywood Termites
In Australia, fumigation for drywood termites is very expensive, yet local (spot) treatments are not without their issues. Apart from the challenge of ensuring all infested areas in the structure are treated, even treating a single area of infestation can be challenging as it can
be difficult to get the treatment to penetrate all the galleries in the wood.
Foams are commonly used to carry out localised treatments for subterranean termites. Researchers in the Queensland Government evaluated two non-repellent actives commonly used in subterranean termite treatments, fipronil and imidacloprid, for their performance on drywood termites in a foam format.2 In summary, whilst both insecticides delivered 100% control when applied topically or as a residue in continuous exposure, imidacloprid did not deliver 100% mortality when the drywood termites were exposed to residues for a short period and indeed, the speed of kill was slower for imidacloprid than fipronil in all trials.
Interestingly, the imidacloprid foam showed high levels of repellency as a residual treatment – up to 90% after 24 hours, whereas the fipronil foam was only slightly repellent when fresh, but non-repellent after 24 hours. These properties resulted in corresponding levels of mortality – low levels with imidacloprid and high levels with fipronil.
Additional trials were carried out with the fipronil foam to assess horizontal transfer. The results demonstrated that fipronil was passed from donor termites to recipient termites. At a 1:1 ratio, 100% mortality of the recipients occurred after approximately two weeks. However, at a ratio of 1 donor to 9 recipients, the mortality rate was slower, and 100% mortality was not achieved even after the 26 days of the study. This is in line with studies on subterranean termites that emphasise the importance of getting the insecticide to as many termites as possible to maximise the donor:recipient ratio and therefore horizontal transfer.
The authors state the need for field trials to confirm performance, with particular concern that for liquids and foams, frass in the galleries may prevent movement of the treatment within the galleries.
As a result of these findings, the same authors investigated the possibility of using synergised pyrethrum in an aerosol format to treat drywood termites.3 The laboratory study demonstrated that synergised pyrethrum delivered very rapid mortality of drywood termites when exposed to treated surfaces. Interestingly, the residual performance was seen to continue for at least two months. Importantly, the aerosol formulation penetrated loose frass barriers, which would allow for more complete treatment in the field. The researchers noted the need to carry out field trials to determine its effectiveness in the field.
References
1 Zilberman, D. and Lewis, V.R. (2024). Economic framework to assess the impact of banning pesticides, with application to sulfuryl fluoride for drywood termites (Blattodea: Kalotermitidae) in California. Journal of Economic Entomology. 117(1): 1-7, https://doi.org/10.1093/jee/toad200
2 Hassan, B et al. (2023). Toxicity, repellency, and horizontal transfer of foam insecticides for remedial control of an invasive drywood termite,
Cryptotermes brevis (Blattodea: Kalotermitidae). BioResources 18(2):2589-2610.
3 Hassan, B and Fitzgerald, F. (2023). Potential of Gas-Propelled Aerosol Containing Synergized Pyrethrins for Localized Treatment of
Cryptotermes brevis (Kalotermitidae: Blattodea). Insects, 14(6): 522. https://doi.org/10.3390/insects14060522
About drywood termites
The West Indian drywood termite, Cryptotermes brevis, is one of the most difficult termites to control and an important invasive termite, with its distinctive pellet-like frass (pictured) helping in its identification. Due to its nesting behaviour, where it develops small nests completely within its wood food source that can survive at low moisture levels, the nests are difficult to detect and easy to inadvertently transport.
When buildings become infested, control is difficult as the standard treatment is to fumigate the entire building, which tends to be expensive and concerning from a safety and environmental point of view. This issue is of particular focus in Australia at the moment, as although the West Indian drywood termite is classified as an invasive pest, the Queensland Government has decided that when an infestation is identified, the cost of the treatment is now the responsibility of the property owner.
Drywood termite control — the heat is on!
With heat treatments being utilised commercially for other pests, the question is whether this is a suitable technique for the control of drywood termites. The challenge in using heat treatment for drywood termites is that whereas treatment of wooden furniture may be possible, treatment of whole buildings becomes more problematic.
Australian researchers have established that although exposure to 40°C for up to an hour did not kill the termites, exposure at 45°C for one hour was lethal.1 Higher temperatures were even more effective — as little as three minutes’ exposure at 50°C or two minutes at 55°C was lethal. The researchers suggested that localised heat spot treatment could be an effective option. However, getting the internal temperature of the wood (where the termites are hiding) up to the required heat level can be a challenge.
However, in the US, heat treatment is increasing in popularity to treat West Indian drywood termite infestations, although they suffer from the same issue, that such treatments may not be able to kill all the termites due to the difficulty in heating some areas. Focusing on blocks of units, where West Indian drywood termites primarily infested wooden furniture and kitchen cabinets, researchers identified ways to improve the heat circulation in treatments.2 The key action they took was to drill holes in the base of kitchen cabinets and pump heated air into these voids. The result was a 100% success rate, rather than a 33% callback rate with standard heat treatments. The researchers emphasised the importance of achieving even heat distribution, not only to ensure control, but to avoid the need to try and heat to excessive temperatures to overcome the failings of poor heat distribution.
References
1 McDonald, Janet & Fitzgerald, Chris & Hassan, Babar & Morrell, Jeffrey. (2022). Thermal tolerance of an invasive drywood termite, Cryptotermes brevis (Blattodea: Kalotermitidae). Journal of Thermal Biology. 104. 103199. 10.1016/j.jtherbio.2022.103199.
2 Tay, Jia-Wei & James, Devon. (2021). Field Demonstration of Heat Technology to Mitigate Heat Sinks for Drywood Termite (Blattodea: Kalotermitidae) Management. Insects. 12. 1090. 10.3390/insects12121090.
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