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FIRST AUSTRALIAN REPORT OF STRUCTURAL INFESTATION BY THE WESTERN DRYWOOD TERMITE

The discovery of western drywood termite damage to the structural timber of a home in Sydney is the first of its kind in Australia, giving authorities cause for concern.

Termite professionals will be aware of drywood termites, although most will not have seen them in the field. However, pest managers need to be on the lookout for drywood termites as their behaviour means traditional termite prevention techniques do not work. Drywood termites directly colonise the wood on which they feed – they do not access buildings through the soil – so traditional soil treatments for subterranean termites will do nothing to prevent an infestation of drywood termites.

Although native drywood termite species are of minimal economic importance, invasive species are a different matter. The West Indian drywood termite, Cryptotermes brevis, is one of the world’s most destructive termite species. It has been present in Australia for decades and is frequently detected in many locations along the east coast, with Queensland subjected to the highest rates of infestation.

Mid-way through 2019 another species of invasive drywood termite was detected in structural roof framing of a home at Kingsgrove in suburban Sydney. The species, Incisitermes minor or western drywood termite, is a common structure- infesting drywood termite in the southwestern United States and northwestern Mexico. The termite has spread across the USA as far as Florida and internationally to Canada, China and Japan largely due to the commercial transportation of wood products. Even though western drywood termite has previously been detected in Sydney in a range of portable timber items including furniture, crates and pallets, the Kingsgrove detection was the first infestation found in structural timber in Australia.

The homeowner raised the alarm after discovering frass pellets (faecal matter) on her bedroom windowsill. These had emerged from a hole in the upper panel of the window frame (Figure 1).

Flick-Anticimex was contacted to investigate the cause of the timber damage. The subsequent inspection by Shannon Vicary and Paul Georgiadis, field supervisors from the Homebush branch, discovered large masses of termite frass and termite alate wings in the roof cavity (Figure 2). Realising the magnitude of the potential threat posed by invasive drywood termites, Flick-Anticimex contacted NSW Government biosecurity authorities. A Greater Sydney Local Land Services (GSLLS) plant biosecurity officer visited the home to look for soldier specimens needed for morphological species identification.

Figure 2: Western drywood termite frass pellets accumulated in the roof of the Kingsgrove house. The cone-shaped pile of frass is characteristic of drywood termites

With the assistance of Flick-Anticimex, several soldiers were collected and taken to a laboratory where they were identified as Incisitermes minor (Figure 3A). The soldiers of western drywood termite and West Indian drywood termite are highly dissimilar. Western drywood termite soldiers have protruding dark mandibles and long, smooth heads with parallel sides and a cone-shaped third basal antennal segment (Figure 3A). West Indian drywood termite soldier mandibles are short and bowed. The head is rough, has frontal lobes and is constricted behind the lobes (Figure 3C).

The source of the infestation was likely to have been timber imported from the USA. The homeowner indicated that while the house was over 50 years old, the rear part was constructed 20 years ago. It was in the roof of this section where evidence of termites and damaged timber were most common (Figure 4). Also, whereas the original structural timbers were hardwood, the newer portion was mostly comprised of softwoods including radiata pine and oregon.

Figure 4: Western drywood termite damage to timber. Undamaged superficial timber was removed to search for termite soldiers upon which to base the species identification

The western drywood termite is a significant pest in the USA, with an estimated annual economic cost of US$250 million. A variety of treatments are available for eradicating drywood termite infestations, including fumigation (methyl bromide or sulfuryl fluoride), thermal treatment (heat or cold), electrocution and chemical treatment. Fumigation is considered to be the only ‘whole-structure treatment’ because of its ability to achieve synchronised and widespread eradication in all wooden members and difficult to access infestations. Given the economic risks, this approach has been the only control option used in Australia for buildings infested by drywood termites to date.

Fumigation with sulfuryl fluoride was the chosen treatment method for the Kingsgrove house. This was undertaken by Rentokil. Household fumigation involved removing certain items such as pets, plants and food, installing fumigant emission pipes and detectors, surrounding the house with a gas-tight layer of plastic sheets or ‘tenting’, pumping gas inside and maintaining concentrations at efficacious levels for a sufficient period of time. Once the gas was released and the ‘tent’ removed, the house was aerated and monitored to ensure it was safe to be reoccupied.

Post-fumigation inspections of the roof were conducted by GSLLS and Rentokil. Results were positive, with dead termite workers and alates being found in several locations. As a further measure of treatment efficacy, frass pellets and alate wings were removed by vacuuming. The reappearance of these items in subsequent inspections may be an indication of ongoing infestation and the need for retreatment.

Further measures as part of ongoing surveillance included the inspection of the roof spaces of adjoining properties and the deployment of sticky traps near lights to detect any termite alates. Thus far nothing has been found. A letter box drop saw an information pamphlet being delivered to local residents apprising them of the risks posed by western drywood termites, informing them of what to look out for and who to notify in the event of suspected detection.

A consequence of the massive increase in imports from overseas, the western drywood termite remains a constant threat and will inevitably be an ongoing cause for concern. Biosecurity is everyone’s responsibility and it is essential businesses and the general public remain alert and report any suspected sightings of this insect, especially in high risk circumstances such as when timber items are imported from overseas.

Pest managers who think they may have seen a western drywood termite should contact the Exotic Plant Pest Hotline on 1800 084 881.

More drywood termite information

Martin Horwood, Senior Plant Biosecurity Officer, Greater Sydney Local Land Services