Research suggests that climate change is having a significant impact on the viability of invasive species becoming established in new territories.
The impact of climate change on pest populations is becoming a hot topic. With significant changes in temperature, particularly minimum temperatures, and changes in humidity already apparent, the potential spread of termites to new areas previously unsuitable for termite survival is a real possibility.
One example is South Korea and the potential establishment of the significant invasive termite Coptotermes formosanus. Researchers have recently modelled the likelihood of the Formosan termite becoming established in South Korea as a result of climate change.1 Currently, there has been no confirmed record of the Formosan termite in South Korea, despite it being present in two neighbouring countries – China and Japan. This is due to the fact that C. formosanus cannot survive in conditions where the average winter temperature is below 4°C, which was the prevailing situation for the vast majority of South Korea, with the exception of Jeju Island. However, with temperatures increasing, this is no longer the case.
Over the last hundred years, the average annual temperature in South Korea has increased 2.09°C. Some southern areas of South Korea now have a climate that would allow Formosan termites to become established. Assuming the temperature continues to increase at a similar rate, by the end of the century, much of the southern part of South Korea would provide conditions that allow the establishment of C. formosanus.
Critical to avoiding the establishment of C. formosanus is to ensure quarantine inspection prevents its introduction in the first place. With the increasing trade from China, Taiwan, Japan and the US, a southern seaport such as Busan is considered a likely entry point.
Switzerland demonstrated that this is not just a theory, when researchers reported the first record of the subterranean termite, Reticulitermes grassei, in 2020.2 This infestation was first detected in 2018 in a home near Lake Zurich (pictured above). The source of the introduction was assumed to have been olive and palm trees planted on the property, as DNA analysis indicated that the termites were similar to populations from southern Spain. After an initial failed treatment using diatomaceous earth, a baiting treatment appeared to have controlled the infestation. However, the fact that two mating flights had been observed means that authorities need to be vigilant regarding further infestations.
Human-assisted pest invasions are a feature of the modern world. For example, researchers in India recently reported that two non-native Coptotermes species – C. testaceus and C. sjostedti – were intercepted at a quarantine station, having been discovered inside incoming timber.3 Undoubtedly, many unsuccessful invasions see the invading pest either being intercepted or failing to establish; yet some are successful and the chances of success can be improved by the ‘bridgehead effect’. This is where an invasive species establishes a population outside its native range, which then becomes the source for further infestations.
Researchers from the US and China have used DNA analysis to establish that a bridgehead was formed in Hawaii, which provided the source for one introduction of Coptotermes formosanus into the southern US in the 1930s.4 Furthermore, they propose that this bridgehead was actually formed in Hawaii from two separate introductions: one from eastern Asia and one from Hong Kong. Along with a second incursion in Florida directly from South-central China in the 1940s, it allowed C. formosanus to become established in mainland US.
It is also important to appreciate that changes in weather patterns not only allow termites to colonise areas that may have previously been uninhabitable, but may also impact their behaviour within their existing range. Changes in temperature, rainfall and seasonality all have the potential to alter foraging behaviour, reproductive cycles and indeed impact species composition in a given area.
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1 Lee, S.-B., Tong, R.L., Kim, S.-H., Im, I.G., Su, N.-Y., 2020b. Potential pest status of the Formosan subterranean termite, Coptotermes formosanus Shiraki (Blattodea: Isoptera: Rhinotermitidae), in response to climate change in the Korean Peninsula. FLORIDA ENTOMOLOGIST 103, 431–437.
2 Ghesini, S., Mueller, G., Marino, M., 2020. First record of the subterranean termite Reticulitermes grassei in Switzerland. BULLETIN OF INSECTOLOGY 73, 149–151.
3 Nagaraju, D.K., Kalleshwaraswamy, C.M., Iyyanar, D., Singh, M., Jain, R.K., Kasturi, N., Ranjith, M., Mahadevaswamy, H.M., Asokan, R., n.d. First interception of two wood feeding potential invasive Coptotermes termite species in India. INTERNATIONAL JOURNAL OF TROPICAL INSECT SCIENCE. https://doi.org/10.1007/s42690-020-00287-5
4 Blumenfeld, A.J., Eyer, P.-A., Husseneder, C., Mo, J., Johnson, L.N.L., Wang, C., Grace, J.K., Chouvenc, T., Wang, S., Vargo, E.L., 2021. Bridgehead effect and multiple introductions shape the global invasion history of a termite. COMMUNICATIONS BIOLOGY 4. https://doi.org/10.1038/s42003-021-01725-x