Steve Broadbent, regional director of Ensystex, examines the curious behaviour of termites eating plastic, as discovered by a team of international researchers.
We all know Australia’s termites have an appetite for destruction. In fact, we like to believe our termites are the most destructive in the world! The reality is, they probably are. Despite our small population size, Australia is the third largest market in the world (by dollar value) for termite treatments as the damage they cause can be so extensive and widespread. But how does the appetite of our termites compare to that of termites from Asia and the US when it comes to non-food sources, such as plastic?
We generally recognise that termites eat cellulose materials, so presumably plastics are not on the menu. After all, most of the service pipes installed in modern buildings are made of plastic. In 2013, a team of termite researchers1 from six countries, including Australia, looked into the appetite that termites have for plastics. Six species of Coptotermes termites from Australia and Asia were studied, together with Mastotermes darwiniensis; and from the US, Reticulitermes flavipes.
It has actually been well documented over the past 60 years that termites do cause substantial damage to plastics, especially in Australia. The susceptibility of plastic materials varies with the type of plastic used, its hardness and the exposed surface area. Results also differ between termite species. Studies by Dr Michael Lenz from CSIRO have previously shown that Coptotermes acinaciformis termites were particularly feisty in attacking plastics.
Based on Dr Lenz’s work, a more comprehensive study was merited due to the practical implications of global trade, whereby a material may be considered to be termite-resistant in one country, whilst in another country it might be considered susceptible to termites. Some countries have experienced serious termite damage to underground communication and power cables. In the case of Australia, these reports date right back to 1911.
Plastics do not o er any nutritional value to termites, so it is bemusing as to why they do attack these materials. Plastic pipes made of four different plastics were evaluated in the 2013 study. These were low-density polyethylene (LDPE), medium-density polyethylene (MDPE), a new polyamide-based plastics (DPPA), and polyamide 12, also known as Nylon 12. These plastic were selected since they have been commonly used as cable sheathings in underground situations in Australia and around the world.
The results allowed for the termite species to be separated into four rankings with respect to their ability to damage these plastics. As we might expect, our Australian termites topped the charts! The most damaging termites, ranked in category one, were C. acinaciformis and M. darwiniensis, from tropical Australia. In the second category were C. acinaciformis from temperate Australia and C. kalshoveni from Southeast Asia. Right at the bottom, in the fourth category, were R. flavipes from the USA, that caused no damage.
With respect to the plastic types, low-density polyethylene was very much the least resistant to attack by termites, while MDPE and DPPA showed intermediate resistance, and PA12 (Nylon 12) was the most resistant.
We have no evidence to show why our native species are so able and willing to damage plastics. Not only did they cause more damage, they attacked a wider range of plastics. The larger mandible size of M. darwiniensis could be a factor in their success at damaging plastics. This sheds no light though on why Australia’s C. acinaciformis complex of termites are so much more damaging when compared to other species in the same genera. I note here, it is generally accepted from DNA studies, that C. acinaciformis is not a single species of termites, but a range of sub- species spread around Australia.
The results show that in Australia we need to be wary of accepting materials determined as being termite-resistant overseas. Even materials considered resistant to C. formosanus, about which so much is written due to its prevalence and ability to cause high levels of damage in northern Asia and the USA, needs to be reassessed in Southeast Asia and Australia. In contrast, materials considered resistant in Australia, such as unplasticised polyvinyl chloride (PVC), are more likely to be resistant overseas.
These studies highlight the importance of using the correct materials when constructing homes and properties in Australia. The Australian Standard AS 3660.1 Termite Management Part 1: New Building Work speci es that below-ground plastic structural elements and ant caps should be made of PVC, with a minimum thickness of 1 mm and a minimum hardness of Shore D 80. This applies to plastic pipes too, which are governed by the plumbing code that forms part of the National Construction Standard (NCS) administered by the Building Code of Australia.
Steve Broadbent, Regional Director, Ensystex
1 M. Lenz, B. Kard, J.W. Cre eld, T.A. Evans, K.S. Brown, E.D. Freytag, J. Zhong, C. Y. Lee, B. H. Yeoh, T. Yoshimura, K. Tsunoda, C. Vongkalung, Y. Sornnawat, T. A. Roland and M. Pommier de Santi. Ability of Field Populations of Coptotermes spp., Reticulitermes flavipes, and Mastotermes darwiniensis (Isoptera: Rhinotermitidae; Mastotermitidae) to Damage Plastic Cable Sheathings. J. Econ. Entomol. 106(3): 1395-1403 (2013).