The latest research looking into the complexities of termite nest structure, swarming behaviour and the roles of the royal pair and reproductives.
Latest termite nest and reproduction research
Predicting termite mound structures
Researchers using computer modelling to predict termite mound shape believe that in applying the principles of heat transfer and thermodynamics, computer-generated mound shapes closely match those found in the field.1 Essentially, sun and wind play an important role in the development of mound shape and structure.
Mounds exposed to more sun tend to have a cone-shaped structure that points towards the sun, whereas mounds in shaded areas tend to be vertical domes. Mounds in areas of increased wind are generally shorter in height. The sun and wind factors interact to determine the internal structure. When the need for thermoregulation is more important than the need for gas exchange, the mounds have thicker walls and are built deeper into the soil.
Outside of tropical rainforests, termite alate flights often occur during a specific time of the year, typically during a warmer, more humid period. Whilst most pest managers will tell you this is the case, researchers in Brazil have confirmed the same whilst assessing alate flights in a seasonally dry tropical forest.2 Peak termite swarms, of all species, occurred during February and indeed 97% of all flights occurred during a 20-day period.
The number of flight occurrences and species composition were significantly influenced by the accumulated precipitation over 72 hours and air density. This high level of synchronisation between species suggests that in environments which have variable moisture levels throughout the year, termites have evolved to swarm when conditions provide the best chance of survival.
1 Fagundes, Tadeu & Ordonez, J. & Yaghoobian, Neda. (2021). The Role of Mound Functions and Local Environment in the Diversity of Termite Mound Structures. Journal of Theoretical Biology. 527. 110823. 10.1016/ j.jtbi.2021.110823.
2 Lucena, Emanuelly & Silva, Israel Soares & Monteiro, Sara & Moura, Flávia & Vasconcellos, Alexandre. (2021). Accumulated precipitation and air density are linked to termite (Blattodea) flight synchronism in a Seasonally Dry Tropical Forest in north-eastern Brazil. Austral Entomology. 61. 10.1111/aen.12577.
Termite Professional Australian edition, 2021
How many termite reproductives are in a nest?
For pest managers carrying out termite work, the holy grail is to find the termite queen (if they are able to find the nest). Many would assume that the termite colony comprises a ‘simple family’ – a single pair of primary reproductives, which mate monogamously. This is the most common situation, but it isn’t always the case.
Termites create two other types of colony structure. Firstly, there is the extended family where one or both of the founding pair are supported or have been replaced by secondary reproductives that have been produced from within the colony. Extended family colonies appear to be more likely in lower termites (60%) compared to higher termites (13%).1
Secondly, there are ‘mixed family’ colonies, which can arise through three different mechanisms: when two dispersing alates found a colony together; from fusion between two simple families; or through adoption of alates.
Researchers in Australia utilised DNA analysis to investigate the prevalence of the different colony types in Nasutitermes exitiosus.
Analysing 60 colonies from across NSW and ACT, the researchers determined that 61.7% were simple colonies, 16.7% were extended families and 21.7% were mixed families. Most of the mixed-family colonies contained two queens and one or two kings. In one colony, the DNA evidence suggested there were seven primary queens. How such mixed family colonies are formed is unclear, with the researchers suggesting that future investigations should focus on the potential impact of local ecological and climatic conditions on breeding patterns and colony structure.
Long live the Queen (and King)
As a general rule in animals there is a trade-off between longevity and reproductive output – you can be either long lived or have a high reproductive output, but you cannot have both. The exception to the rule are social insects, especially the termite queens and kings, which can live for 20 years or more.
In their review on the subject, Tasaki et al. (2021)2 point out that a range of external factors rather than ageing per se impact life expectancy – predation, starvation and adverse weather events will all cause death. However, in a colony situation, the termite reproductives that remain safe in the centre of the colony and are protected and fed through the activity of other colony members are largely insulated from these mortality factors. Thus the development of eusociality with the subsequent removal of these pressures on the reproductives is one of the key reasons why they live so long.
However, there must also be a physiological and molecular basis to the longevity; there must be a delay in the ageing process that is normally seen in other animals. There is evidence to suggest that the antioxidant and DNA repair systems are augmented to slow the age-associated accumulation of physiological damage. An alternative theory (not mutually exclusive) is that reproductives have a lower expression of growth signalling pathways, which prevents the reduction in gene expression that occurs later in life.
Another factor that may contribute to their longevity is the hypoxic nature of the royal chamber. Deep in the nest, the oxygen levels are low (15%) and CO2 levels are high (5%). In the atmosphere, oxygen content is around 21% and CO2 levels are less than 0.05%. Clearly, reproductives have had to adapt to this very different atmosphere inside the nest and indeed queen egg-laying increases greatly under these nest conditions, compared to normal atmospheric conditions.3 These lower levels of oxygen would reduce oxidative stress on reproductives (oxygen can be toxic) and the development of anaerobic energy producing systems in these low-oxygen environments may also contribute to their long lifespans, but this needs to be investigated further.
1 Montagu, A., Lee, T.R.C., Ujvari, B., McCarl, V., Evans, T.A., Lo, N., 2020. High numbers of unrelated reproductives in the Australian `higher’ termite Nasutitermes exitiosus (Blattodea: Termitidae). INSECTES SOCIAUX 67, 281–294. https://doi.org/10.1007/s00040-020-00764-7
2 Tasaki, E., Takata, M., Matsuura, K., 2021. Why and how do termite kings and queens live so long? PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES 376. https://doi.org/10.1098/ rstb.2019.0740
3 Tasaki, E., Komagata, Y., Inagaki, T., Matsuura, K., 2020. Reproduction deep inside wood: a low O-2 and high CO2 environment promotes egg production by termite queens. BIOLOGY LETTERS 16. https://doi.org/10.1098/rsbl.2020.0049
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