In-ground termite baits are a provide method for protecting buildings. However, latest research suggests that it may not be the best method for Coptotermes gestroi, due to its different foraging behaviour.
Termite baits are a proven termite management tool, especially when targeting colony elimination. Although the speed of performance differs between the various termite species (due to differences in moulting behaviour), as long as the termites feed on the bait, the colony will eventually be eliminated. For above-ground baits placed at feeding sites, there is a very high probability that the termites will feed on the bait and the colony will be controlled. However, the use of termite bait in in-ground termite monitoring and baiting systems is reliant on the termites finding the bait stations. The system is based on the principle that by placing bait stations close together around the property, termites will be intercepted by at least one of the bait stations before reaching the building. This has proven to be a very successful management tool for a number of termite species, including many Coptotermes species, but results with Coptotermes gestroi have been mixed. Researchers have been trying to find out why.
Field studies in a number of locations have shown Coptotermes formosanus to have hit rates of around 17%, whilst C. gestroi has hit rates as low as 1.7%. Indeed, a recent study in Florida, in the US, evaluated above-ground and in-ground bait station hits for Coptotermes gestroi. Of the 83 in-ground bait stations placed around infested buildings and trees in the study, none were intercepted by the termites. Researchers suspected it was due to the termites’ foraging behaviour, specifically tunnel geometry.
In laboratory trials, the researchers set up two-year-old termite colonies in the middle of a 1 m x 1 m foraging arena. The foraging arena consisted of two Plexiglas plates separated by a 0.2 cm gap. The gap was filled with sand, with a wood disc placed in each of the four corners of the arena. The number of wood discs intercepted by the termites before they reached the edge of the arena was noted and their foraging pattern was recorded. The study utilised five C. formosanus colonies and four C. gestroi colonies.
The results demonstrated that C. formosanus colonies intercepted significantly more wood discs than C. gestroi. Further, there were significant differences in their foraging pattern and tunnel geometries; C. formosanus produced more primary and secondary tunnels, in a highly branched structure, whereas C. gestroi produced longer primary tunnels and shorter secondary tunnels with minimal branching.
These two different foraging patterns can be related to potential search strategies – a highly branched tunnel system being ideal for an area-based search strategy and a long, linear tunnel system being optimal for a distance search strategy. This observed tunnelling pattern for C. gestroi offers a potential explanation as to why in-ground bait stations have a low hit rate in the field (in Florida).
It is important to state, “in Florida”, as results of the foraging patterns in different studies, in different parts of the world have produced variable, sometimes contradictory results, including C. gestroi building highly branched tunnels! The researchers have hypothesised that a number of different factors may impact the foraging behaviour of C. gestroi. The abundance and size of food sources may impact the search strategy/tunnelling formation, as may the environmental conditions and soil type. It is also hypothesised that colony age may impact search strategy, with small colonies having too few termites to build an extensive branched tunnel network. It is likely that there are some differences between species, as illustrated here between C. formosanus and C. gestroi, and such differences could be innate or selected for over time. The researchers indicated a lot more research is required to test these hypotheses, but the bottom line is that in-ground bait stations are not a suitable termite protection system for C. gestroi.
Whilst details of the foraging patterns of Australian termites have not been characterised, leading registered products have been field tested against the Australian termite species. So if the species is on the label, the in-ground bait stations would have been found by the termites in these trials.
Further reading: Su, N-Y and Lee, S-B (2023). A comparison of tunnel geometry between the Formosan subterranean termite and the Asian subterranean termite (Blattodea: Rhinotermitidae). Pest Management Science 79 (10): 3999-4003. https://doi.org/10.1002/ps.7594
