The latest research into termite foraging behaviour looks into the role of the soldier caste and answers questions about preferential food sources.
The impact of environmental factors on foraging behaviour
In a termite inspection report, the pest manager will record the potential risk level of a termite attack as low, moderate, high or very high. But what are the key factors that increase the risk of termite attack?
Using in-ground monitoring stations, researchers in Indonesia1 mapped termite activity across a city and determined that soil characteristics and climate(temperature and humidity) impacted the incidence of termite attack, but didn’t affect the intensity or frequency of termite attack. In particular, with reference to soil characteristics, it appeared that increased levels of clay in the soil was correlated with increased termite activity (clay packing illustrated above), probably due to its higher nutrient content and optimal texture for tunnelling and nest building.
In a more in-depth study on Coptotermes formosanus, researchers2 found that termites preferred monitoring stations containing clay, rather than stations filled with other soil types or those left unfilled (wood only). Monitoring stations containing clay were not only preferred, but under low moisture conditions increased the survivorship of termites (they had a high body water percentage) and resulted in increased wood consumption. Interestingly, different clay soils were preferred at low and moderate moisture levels – bentonite was preferred at low moisture levels and chlorite or attapulgite preferred at moderate moisture levels. The researchers concluded that the preference for bentonite at low moisture levels was due to its ability to retain moisture whereas the preference for chlorite and attapulgite at moderate moisture levels (where the risk of desiccation was minimal) was possibly based on the increased ability to acquire micronutrients from these soils.
Although having an understanding of the general foraging behaviours of termites is important, when considering how termites are likely to behave in a particular situation, it is important to take into account local conditions. Researchers mapping termite activity in eucalyptus plantations in Africa,3 using in-ground monitoring stations, found that temperature was positively correlated with the number of baits attacked and amount eaten, as expected. But they also found that termite activity actually increased through the dry season, which on the face of it may seem counterintuitive, as termites have a need for moisture and high humidity. However, in this particular environment, alternative food sources became scarce during the dry season leaving the eucalyptus plantation and the monitoring stations as the only significant food source. In addition, although subterranean termites do require an environment with high humidity, overly wet or waterlogged soil makes movement difficult in the wet season and lowers the soil temperature, potentially reducing termite activity.
It is important to appreciate that conditions outside a building in the soil are very different to the conditions inside a building. For example, even in cooler months termite activity inside a building may continue, especially in buildings with heating. However, the external conditions are certainly important when assessing the risk of attack and identifying potential entry points. External conditions can also influence the placement of in-ground monitoring or bait stations, to maximise station discovery and termite attack.
Do termites focus on larger food sources?
It makes sense for termites to recruit to the largest food source in their territory. Obviously in many cases this is a building. Termites tend to forage in areas where the surface soil contains more moisture, which tends to be under large objects such as fallen trees, but can termites really determine whether one food source is bigger than another?
Recent laboratory research with Nasutitermes corniger assessing termite reaction to food sources (by varying the number of wooden blocks offered), suggests that the initial exploration and initial recruiting behaviours are not influenced by the size of the food source. However, mass recruitment was significantly higher to the larger wood sources, suggesting that termites are capable of discriminating between food sources and selecting the larger resource.4
The role of soldiers in foraging
The soldier caste, as the name suggests, is integral to the defence of termite colonies. However, recent research also indicates that soldiers have a role in foraging too.5
Carrying out a series of laboratory trials using Nasutitermes corniger, researchers compared the foraging performance of groups comprising 30% soldiers (the natural ratio found in the field) to the performance of groups containing no soldiers. Groups with soldiers occupied a larger number of food sources more quickly than groups without soldiers. In addition, when the size of food resources was manipulated, groups containing soldiers were faster to switch their foraging effort to the larger food resources.
The researchers concluded that the presence of soldiers in foraging groups promotes faster decision-making during foraging. On the face of it, having a foraging force comprising 30% soldiers – termites unable to actually collect food due to their nasute heads – would make foraging less efficient. So from an evolutionary point of view, the efficiencies gained through the increased speed in decision-making and the exploitation of larger resources due to the presence of soldiers must offset the drop in efficiency by having fewer workers in the foraging party.
Termites are always looking for new food sources
It’s not uncommon to observe different termite species utilising the same resources and even the same tunnels. But is this just by accident or could there be some other factors at play? Working with Nasutitermes corniger, a group of researchers in Brazil investigated whether odour cues left by different colonies of the same species or from colonies of different species impacted food choice.6
The studies showed that the termites could detect chemical cues left by different N. corniger colonies but they seemed unable to detect chemical cues of Coptotermes gestroi, which was used as the different species in this trial. Although workers followed trails with their own chemical cues for a longer distance than trails made using chemical cues from other colonies, when the odours from other colonies were added to a food source, the termites preferred these food sources to food sources containing their own chemical cue. Indeed even food lacking in any termite chemical cues were preferred to food with their own colony odour. This would suggest that termites actively discover and evaluate new food sources over previously detected food sources and that chemical cues from other colonies may aid in this decision.
Assuming this behaviour is replicated across termite species, it suggests that fresh termite baits lacking in colony chemical cues placed at foraging sites will be actively explored. Acceptance however, will depend on bait palatability.
1 Arif, A., Putri, G., Muin, M., 2020. Hazard Mapping of Subterranean Termite Attacks in Makassar City, South Sulawesi, Indonesia. INSECTS 11. https://doi.org/10.3390/insects11010031
2 Jin, Z., Chen, J., Wen, X., Wang, C., 2020. Effects of clay materials and moisture levels on habitat preference and survivorship of Formosan subterranean termite, Coptotermes formosanus Shiraki (Blattodea: Rhinotermitidae). PEERJ 8. https://doi.org/10.7717/peerj.10243
3 Alamu, O.T., Ewete, F.K., n.d. Influence of seasonal changes, weather factors and soil depth on the foraging activities of subterranean termites in Eucalyptus plantations. INTERNATIONAL JOURNAL OF TROPICAL INSECT SCIENCE. https://doi.org/10.1007/s42690-020-00311-8
4 de Souza, T.S., Gazal, V.S., Aguiar-Menezes, E. de L., Fernandes, V.J., Leite-Mayerhofer, A.M., 2020. INFLUENCE OF THE AMOUNT OF FOOD RESOURCES IN THE FORAGING BEHAVIOR OF Nasutitermes corniger (MOTSCHULSKY). BIOSCIENCE JOURNAL 36, 48–56
5 Marques do Sacramento, J.J., Cristaldo, P.F., Santana, D.L., Cruz, J.S., dos Santos Oliveira, B.V., dos Santos, A.T., Albano Araujo, A.P., 2020. Soldiers of the termite Nasutitermes corniger (Termitidae: Nasutitermitinae) increase the ability to exploit food resources. BEHAVIOURAL PROCESSES 181. https://doi.org/10.1016/j. beproc.2020.104272
6 Silva, A.N.F., Silva, C.R., Santos, R.E.C., Arce, C.C.M., Araujo, A.P.A., Cristaldo, P.F., 2021. Resource selection in nasute termite: The role of social information. ETHOLOGY 127, 278–285. https://doi.org/10.1111/ eth.13125
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