Termite researchers in the US have investigated the preferred temperature conditions of two Coptotermes species. 

Temperature plays an important role in termite activity, with some species being particularly sensitive to changes in moisture and temperature. It can affect not only their wood consumption rate, but also their tunnelling activity, food transportation activities and ultimately determine their overall survival.

In August 2019, researchers Dr Nan-Yao Su, Dr Thomas Chouvenc and Jayshree Patel from the University of Florida, USA, published a study in Journal of Economic Entomology that looked at the temperature preferences of two invasive subterranean termite species in the US: Coptotermes gestroi and Coptotermes formosanus, and their lab-reared hybrids. These two species are of major concern and cause important economic impact worldwide, with both C. gestroi (tropical) and C. formosanus (warm temperate/subtropical) becoming established in the US state of Florida within the last 40 years.

Although hybrid colonies, formed by mating between these two species, have yet to be found in the field, studies have indicated that lab-reared hybrid colonies show hybrid vigour – the colonies grow faster and have more colony members than the pure-bred colonies. If this hybrid vigour also occurs in the field, it could have important implications for termite management in the range where the hybrid exists.

In this study, the researchers tested the temperature preferences of hybrid worker termites and their parental Coptotermes species by determining the hot and cold boundaries of the live and active termites. They did this by creating a clever ‘thermal bridge’ – a 100 cm aluminium strip with the two ends bent vertically downwards. One end was contained in ice water (zero degrees) and the other end in boiling hot water (100 degrees). One group at a time, the researchers released the termites in the centre of the bridge and noted their activity levels, noting the temperature range where they were most active.

It should be noted that this methodology, whilst potentially useful for determining the preferences and survival of individuals or small groups of termites – possibly analogous to foraging for short periods away from the nest – it does not necessarily correlate with the behaviour, or temperature preferences of colonies over longer periods.

However, in terms of the cold boundary, C. formosanus termites were active as low as 11 degrees while for C.gestroi the lowest temperature where they were active was 22 degrees. This is to be expected as C. formosanus is a temperate species and C. gestroi is a tropical species. For both hybrid species – whether formed from a female C.gestroi or female C. formosanus – the cold boundary was 25 degrees. It was apparent that the Coptotermes hybrid species were far less tolerant of cold conditions than the parent species and more in line with the tropical C. gestroi.

In fact, for C. formosanus, termites were observed to still be alive in conditions as low as 7 degrees, whereas for all other termites, the lowest temperature they could endure was around 18 degrees.

In terms of the hot boundary, the termites all exhibited similar behaviour, being active up to 39 degrees and surviving temperatures up to 47 degrees.

What does this mean for the hybrid species? Both hybrid combinations (whether the female was C. gestroi or C. formosanus) avoided low temperature zones from 8-22 degrees and became more active in zones with temperatures above 25 degrees. However, the largest number of live and active hybrid termites were distributed in the temperature range of 35-39 degrees.

These results suggest that the temperature ranges of these Coptotermes hybrids are not as broad as expected and are actually more in line with the tropical parent, C.gestroi. This would suggest that the hybrid termites, if the species were to become established, would be more active in warm climates than cold climates. If hybrids occurred in temperate regions, they would probably be less active in the cooler months. However, although temperature tolerance is an important measure in determining survival – termite colonies can survive a remarkably wide temperature range – relative humidity is probably the biggest factor in determining colony success and termite survival (Theo Evans, pers. comm.).

Despite the fact these hybrid colonies can be readily founded in the laboratory – alates of the two species will readily mate with each other – colonies in the eld have yet to be identified and it is unknown whether hybrid colonies can produce viable alates themselves. Nevertheless, the ongoing research in this area keeps the industry ahead of the curve should the hybrids establish in the wild.

Further reading: Patel, J., Chouvenc, T. and Su, N-Y (2019). Temperature Preference of Two Invasive Subterranean Termite Species and Their Hybrids (Blattodea: Rhinotermitidae: Coptotermes). Journal of Economic Entomology. 10.1093/jee/toz210.

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