Research suggests that climate change is having a significant impact on the viability of invasive species becoming established in new territories.
Latest climate change and termite research
In discussions regarding the impact of climate change on termite behaviour, there is a general perception that a warming environment and changing rainfall patterns will allow termites to increase their distribution. However, it is more complicated than that. Termite physiology and behaviour, and their relationship with their symbiotic gut microbes has evolved over millions of years; how they may respond to a rapidly changing climate is largely unknown and the subject of increasing research.
The impact of temperature
The potential impact of temperature increases is one obvious influencing factor. It’s also important to realise that changes to the climate are likely to impact different species in different ways. Recent research on the termite fauna in Ghana, Africa, has suggested that savanna termite species have wider thermal tolerance limits than forest termite species, which is not surprising given the wider temperature ranges experienced in the more exposed savanna environment.1
The impact of rainfall
It is also incorrect to assume that the same factors drive species distribution in different parts of the world. In most tropical regions, termite abundance and species diversity are assumed to increase with increasing rainfall, with the highest levels of abundance and diversity found in rainforests. However, it appears in Australia that it is the reverse. Assessing species distribution in Australia across savanna, sclerophyll forest and tropical rainforest, researchers found that the highest species diversity and abundance in termites occurred in the low rainfall, savanna sites.2 Only five species were recorded in the rainforests, all wood-feeding species. The researchers concluded that in Australia, other environmental or habitat-related factors shape species distribution.
The impact on gut microbes
In considering the impact of changing climate on termites, much of the focus has been on the potential effect of increasing temperature on the distribution of species and their behaviour, but very little on the impact of their symbiotic gut bacteria, which are critical for their survival. It is hypothesised that since these gut bacteria have evolved along with the termites and therefore have become very specialised, they will also be less adaptable to changes in temperature.
Looking at the impact of temperature on the gut microbial community of Reticulitermes flavipes, researchers measured changes in the makeup of the gut microbe community over a four-week period at three different temperatures: low (15°C), medium (27°C) and high (35°C).3 Whilst the gut microbes in the medium temperature group were similar to field populations and not greatly different to the gut makeup of the low temperature group, the gut microbes present in the high temperature group had changed significantly. Whilst the researchers could not draw any firm conclusions as to the impact of these changes, termite survival in the high temperature group was significantly lower than in the lower temperature groups. The researchers suggested that future work should focus on the potential impact of changes in gut microbe communities on the various termite metabolic processes and behaviours.
Termite species distribution and dispersal
There is an increasing focus on mapping out the global distribution of termite species. Not only is this important in any assessment of the impact of climate change, but it is also important in understanding the risks in further human-mediated transport of invasive termite species, which can have a significant economic and environmental impact.
Mapping species distributions
Whilst many of the pest termite species are well known, it is important to acknowledge that our general understanding of the termite species present in many countries is largely unknown. Using Thailand as an example, researchers have reviewed termite research papers over the last 56 years to compile a list of confirmed termite species.4 Collectively the papers covered 44 defined locations across Thailand. The papers recorded 75 termite species, with the predominant species across all regions being Globitermes sulphureus, Macrotermes gilvus, Microcerotermes crassus, and Microtermes obesi. However, the papers also recorded some 83 unknown species of termites! Mapping of existing termite species is of course important to determine whether an incursion has occurred. An example is the recent discovery of the drywood termite Glyptotermes nakajimai in the Korean Peninsula. Is this a recent incursion, and is it human mediated? 5
Termite incursions and dispersal
Human-mediated movement of goods remains the key mode of travel for invasive pests. This is true not only for drywood termites, which can exist as nests within small pieces of timber, but for subterranean termites too.
Coptotermes gestroi is found in many Asian countries and has also been confirmed in the US and South America. Although officially recorded as present in Northern India, there is some doubt as to whether it is actually present in India.6 However, a number of dead alates were recently identified in a packing box that had arrived from Harrisonburg, Virginia, USA. Although this interception is not expected to have given rise to a successful colony founding (as the alates were all dead), it does indicate that such intrusion pathways exist.
Whilst there will be significant genetic diversity of a species within its native range, the founding colony in an invasion event will have a specific genetic profile. This allows the use of genetic analysis to map the spread of invasive species. Researchers have used this technique to map the spread of Reticulitermes flavipes, by looking at the genetic makeup from 23 native populations in the US and six introduced populations in other countries.
Even within a native range, it is normal for populations to be somewhat isolated geographically and therefore develop a unique genetic profile. However, the researchers established that even within the US, there was quite clear evidence of movement between discrete populations — highly different genetic individuals were found within the same locality and highly similar genetic individuals were found in locations separated by thousands of kilometres.7 This could only be explained by extensive, human-mediated transfer. Whilst this made it more difficult to pinpoint the source of incursions in other countries, the researchers confirmed that the US was the source of incursions in Canada, Chile and France. They further established that the incursion in France became a bridgehead for further introductions into Canada and Chile.
The US is not the only source of termite incursions. Nasutitermes corniger was first detected at Dania Beach in Florida in 2001, probably arriving from South America or the Caribbean.8 However, control attempts did not start until two years later. In 2016 a second population was detected 21 km away and genetic analysis confirmed it to be derived from the original colony in Dania beach, with human transport from one location to the other the likely route of dispersal. As an invasive termite to the US, authorities are focused on eradicating the incursion before it has the chance to establish.
Human-mediated transport of termites is not only an issue between countries but also within countries. Coptotermes formosanus is an invasive termite to the US, with its origin likely in Asia, possibly via Hawaii. It is currently established in the south-eastern states of the US, as far west as Texas. Obviously, it would be ideal to contain its spread as much as possible. However, a recent Coptotermes formosanus infestation was detected in Riverside County, California.9 Whereas two previous incursions in California were determined to have come from within the US, genetic analysis of this new incursion determined that the termites had come from Asia.
Not only subterranean and drywood termites…
Much of the focus on human-mediated termite dispersal has focused on subterranean and drywood termites as their association with wood makes them a more likely candidate for hitchhiking. However, a recent discovery in Japan suggests that soil-nesting, soil-feeding species can also be accidentally transported.10 Pericapritermes nitobei has been recorded on Okinawa Island, despite not being detected during previous extensive termite surveys on the island. The researchers concluded that this was likely a human-mediated incursion. Due to its similarity to the soil-nesting, fungus-growing termite Odontotermes formosanus, which is a pest of forestry and agriculture, the researchers suggested that other non-wood-feeding, non-wood-nesting termites could also be transported by human activity.
Invasive termites can have wide-ranging impacts
Whilst the main concern regarding invasive termites is the potential damage they can do to human structures, termites can also damage agricultural and forestry crops. As an invasive organism, they have the potential to upset the ecological balance in the environments they invade. Evans (2021) notes that about 25% of invasive termites have spread from urban into periurban, forested habitats.11 Although the spread may be slow due to long generation times and short dispersal alate flights, they have the potential to cause significant economic and ecological damage, especially Coptotermes species, which can attack and kill living trees, and develop into large colonies.
More information on termites.
1 Woon, Joel & Atkinson, David & Adu-Bredu, Stephen & Eggleton, Paul & Parr, Catherine. (2022). Termites have wider thermal limits to cope with environmental conditions in savannas. Journal of Animal Ecology. 91. 10.1111/1365-2656.13673.
2 Clement, Rebecca & Flores-Moreno, Habacuc & Cernusak, Lucas & Cheesman, Alexander & Yatsko, Abbey & Allison, Steven & Eggleton, Paul & Zanne, Amy. (2021). Assessing the Australian Termite Diversity Anomaly: How Habitat and Rainfall Affect Termite Assemblages. Frontiers in Ecology and Evolution. 9. 657444. 10.3389/fevo.2021.657444.
3 Arango, Rachel & Schoville, Sean & Currie, Cameron & Carlos-Shanley, Camila. (2021). Experimental Warming Reduces Survival, Cold Tolerance, and Gut Prokaryotic Diversity of the Eastern Subterranean Termite, Reticulitermes flavipes (Kollar). Frontiers in Microbiology. 12. 10.3389/ fmicb.2021.632715.
4 Lertlumnaphakul, Watthanasak & Ngoen-Klan, Ratchadawan & Vongkaluang, Charunee & Chareonviriyaphap, Theeraphap. (2022). A Review of Termite Species and Their Distribution in Thailand. Insects. 13. 186. 10.3390/insects13020186.
5 Shim, Jaeil & Park, Haechul & Ju, Ho-Jong & Song, Jeong-Hun. (2021). First record of the termite family Kalotermitidae (Blattodea: Termitoidae) in Korea. Journal of Asia-Pacific Entomology. 24. 10.1016/j. aspen.2021.08.017.
6 Venkatesan, Thiruvengadam & Kalleshwaraswamy, C. & Gupta, Ankita & R., Ashika. (2021). Intrusion Pathway of Invasive Asian Subterranean Termite, Coptotermes gestroi (Wasmann) from The Neotropics into The Indian Mainland. Current Science. 120. 1778-1781. 10.18520/cs/v120/ i11/1778-1781.
7 Eyer, Pierre-André & Blumenfeld, Alexander & Johnson, Laura & Perdereau, Elfie & Shults, Phillip & Wang, Shichen & Dedeine, Franck & Dupont, Simon & Bagnères, Anne-Geneviève & Vargo, Edward. (2021). Extensive human-mediated jump dispersal within and across the native and introduced ranges of the invasive termite Reticulitermes flavipes. Molecular Ecology. 30. 10.1111/mec.16022.
8 Thorne, Barbara & Alspach, Sue & Tenn, Katherine & Clark, Marah. (2021). Actions Toward Containment, Control, and Eradication of Invasive Conehead Termites (Blattodea: Isoptera: Termitidae). Journal of Integrated Pest Management. 12. 10.1093/jipm/pmab015.
9 Tseng, Shu-Ping & Boone, Jason & Boone, Lowell & King, Natalee & Taravati, Siavash & Choe, Dong-Hwan & Lee, Chow-Yang. (2021). Genetic Analysis of Formosan Subterranean Termite (Blattodea: Rhinotermitidae) Populations in California. Journal of Economic Entomology. 114. 10.1093/ jee/toab077.
10 Nozaki, Tomonari & Hojo, Masaru & Yashiro, Toshihisa & Matsuura, Kenji. (2021). First Record of the Soil-feeding Higher Termites (Isoptera: Termitidae) from Okinawa Island, the Central Ryukyus, Japan. Sociobiology. 68. 6159. 10.13102/sociobiology.v68i2.6159.
11 Evans, Theodore. (2021). Predicting ecological impacts of invasive termites. Current Opinion in Insect Science. 46. 10.1016/j.cois.2021.03.003.
Termite Professional Australian edition, 2021
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.
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