Researchers from the University of Florida have worked out a novel way to determine the size of a termite colony – by measuring the amount of wood the termites consume.
Conducting experiments on subterranean termite colonies in the eld is often a challenging task for entomologists and researchers due to their cryptic foraging behaviour, unobservable nesting habits and inability to accurately estimate colony size. As a result, historically a large amount of termite research has been carried out in laboratory studies using small groups of field-collected termites. However, the results of such studies are often challenged as being unrepresentative of the behaviours exhibited by a complete colony, with all the castes in play.
More recently, researchers have started carrying out trials on entire colonies bred in the laboratory. This certainly gives the researchers more control over the experiments but measurement of colony size – a key parameter in many trials – still represents a problem. Researchers could do mark/recapture studies, a common method for estimating populations of animals, but the act of marking termites could well impact behaviour through causing stress or changing chemical cues. Complete destruction of the nest at the end of the trial will certainly provide a definitive answer, but when several years have been spent growing the colony, it would be hoped that they could be used for more than one trial!
Researchers from the University of Florida, led by Professor Nan-Yao Su, set out to develop a procedure to estimate colony size without impacting the behaviour of the termites or destroying the colonies, the findings of which were published in Journal of Economic Entomology in January 2020.
The objective of the study was to determine whether the average daily wood consumption of a whole colony could be used to accurately infer the size of laboratory- kept colonies. The team hypothesised that colony-wide wood consumption would be proportional to colony size. They also looked at the relationships between daily wood consumed and different colony variables such as the total number of individuals, colony mass, number of workers, and number of soldiers.
In this study, the team studied three- and four-year old lab-reared colonies of two Coptotermes species, C. formosanus and C. gestroi, and their hybrids. The termites were given access to wood that had been weighed, then one week later, the remaining wood was removed and weighed again. This told the researchers how much wood had been consumed over a week, which was then divided by seven to give the daily wood consumption rate of each colony. After the wood consumption calculations had been made, they measured colony mass (by weight) and determined the total number of termites, total worker mass, number of workers, number of soldiers, and soldier ratio.
The findings showed a clear link between the daily wood consumption of the termites and several variables. The strongest link was between daily wood consumption and the total number of termites in the colony; the higher the amount of wood consumed, the higher the number of termites. The same was true of the total number of worker termites – more worker termites existed in the colonies where a large amount of wood was consumed daily. This is presumably because workers are the caste responsible for wood consumption.
Therefore, the researchers concluded that in the lab setting, the average daily wood consumption of a subterranean termite colony can be reliably used to infer colony size. So what do the findings mean?
For termite researchers it means they now have a reliable method of determining the size of a termite colony before they start an experiment. Determining laboratory colony size will now require a fraction of the time and resources, with minimal disturbance, stress, and mortality to the termites. The researchers concluded that colony size of C. formosanus and C. gestroi (and their hybrids) can be confidently estimated for colonies comprising between 10,000 and 100,000 termites.
This wood consumption method of inferring colony size will be used in an upcoming series of large-scale and colony-wide studies (up to several million termites from colonies with more than 50,000 termites each) undertaken by the University of Florida research group. If the method of inferring colony size proves to be accurate, after repeat experiments, it will be interesting to see if over the coming years it might be possible to relate the lab results to estimating colony size in the field.
How much wood?
Coptotermes formosanus’ wood consumption was measured at approximately 4 g/ 40,000 workers per day. Extrapolating to a large colony with a million workers, the colony would consume 36.5 kg of wood per year.
Further reading: Patel, J., Lee, S-B., Chouvenc, T. & Su, N-Y. (2020). Inferring Termite Colony Size Using Wood Consumption in Subterranean Termites (Blattodea: Rhinotermitidae) in Laboratory-Rearing Conditions. Journal of Economic Entomology. 10.1093/jee/toz353.