A review of the latest research on termite baiting, including a look at potential new bait actives and novel baiting strategies.
Latest termite baiting research
The mode of action of chitin synthesis inhibitors
Chitin synthesis inhibitors are proven to deliver colony control in termites. The key to their success is their delayed mode of action (only activated when termites moult) and that termites exhibit trophallaxis, which allows for any CSI ingested by foraging termites to be distributed through the colony. However, in the field, as only a relatively small proportion of the workers actually forage, the question arises as to what proportion of foragers actually need to feed on a CSI bait for colony elimination to occur?
Working with four-year-old laboratory colonies of Coptotermes gestroi, researchers exposed workers to termite bait for five days before being returned to their colonies.1 The number of exposed workers that were returned to the colonies was varied to create a proportion of exposed workers varying from 0% to 5% of the overall worker population. Colony elimination was confirmed for all colonies where 5% of the worker population had fed directly on bait and two thirds of colonies where 2.5% of the worker population had been exposed. The results confirmed that only a small percentage needs to have fed on a bait for colony elimination to occur and for C. gestroi, it appears that somewhere between 2.5% and 5% of the worker population would be sufficient.
The primary action of chitin synthesis inhibitors is on the moulting process. Workers die when they moult, and younger workers die before the older workers as they have a shorter inter-moult period. Indeed, the workers in higher termites, which do not moult, are not directly affected by the bait. The developing larvae also actively moult and are eliminated early in the baiting process. However, researchers wanted to know whether the lack of replacement brood was due to the queen being unable to lay viable eggs, or that she laid the eggs but the eggs hatched and were unable to moult from the first instar.
Working with founding pairs of Coptotermes gestroi in the laboratory, Chouvenc and Lee (2021) exposed these new colonies to CSI from day one.2 The impact was profound. Even by day ten, the number of eggs produced by the CSI-exposed colonies was significantly lower than the control colonies. By day 20 the number of eggs in the treated colonies started to decline and whilst control colonies started to produce larvae by day 35, the treated colonies never produced larvae. After 110 days, all the treated colonies were dead, although it is unclear as to whether the death of the queen and king was due to lack of alloparental care, as a direct consequence of the CSI exposure, or both.
The researchers concluded that the queen is indeed impacted by ingesting CSI and is unable to lay viable eggs, contributing to the collapse of the colony.
Independent confirmation of Coptotermes gestroi colony control by novaluron
Although a range of chitin synthesis inhibitors are used in termite baits, most of the research has used the older chitin synthesis inhibitors such as hexaflumuron and noviflumuron. Independent data on new chitin synthesis inhibitors, such as novaluron, is of course more limited. Although proven on Reticulitermes species and Coptotermes formosanus in the US, its performance on Coptotermes gestroi has not previously been evaluated. Researchers in the US have confirmed novaluron as an effective colony elimination active using complete laboratory colonies of C. gestroi in foraging arenas (Figure 1) where feeding sites were 15 metres from the nest.3 The study demonstrated that the termites had stopped feeding within six weeks and colony elimination had occurred within three months.
Baiting fungus-growing termites
Termite baiting has primarily been a control method for lower termites. Its success against higher termites is more variable. Workers in higher termites do not moult and so this would at least partly explain why bait-affected colonies of higher termites take longer to succumb. However, some of the higher termite species are fungus growers. The fungus is used to digest cellulose material and/or provide a direct food source for the termites, depending on the species. The inclusion of this fungal partner in the processing of food is also thought to impact the passage of the chitin synthesis inhibitor within the colony.
Many of the fungus-growing species are also more sporadic in their foraging patterns, regularly abandoning food sources before they are exhausted. Whilst baiting has been successful in mound-building, fungus-growing termites, where the bait can be applied directly to the mound, dealing with fungus-growing species without a mound can be more problematic.
Researchers in Pakistan investigating the fungus-growing termite Odontotermes obesus demonstrated that larger bait stations are found more easily, experience higher levels of recruitment and suffer from significantly less abandonment than smaller bait stations.4 The researchers thus concluded that in order to get sufficient bait into the colony, large bait stations (around 8 L in volume) would work better for O. obesus and other related fungus-growing higher termites.
Fungus-growing termites are significant pests in Asia, particularly of agricultural crops rather than buildings. Whilst the length of time to achieve eradication in the urban setting is critical, as damage to buildings needs to be arrested as soon as possible, complete elimination in the agricultural setting is less important. Instead, any reduction in crop damage is deemed valuable. However, control methods have to be applied over a large area in order to reduce termite activity. To avoid spraying chemical around food crops and for reduced environmental impact, termite baiting is seen as a preferred option.
Researchers in Taiwan have completed a four-year study assessing the impact of termite baits in reducing the activity of Odontotermes formosanus.5 Using long-lasting termite baits, the number of monitoring baits attacked had dropped by nearly 50% after two years of baiting, and the amount of wood consumed had dropped by 25%. The colonies that had been confirmed as eliminated all had chitin synthesis inhibitor in the fungus gardens. However, the baiting had not eliminated all the colonies in the area. Despite this, the researchers believe the significant drop in wood consumption would translate to a beneficial drop in crop damage. Further work around density and location of bait stations could potentially increase the level of control achieved.
Fungi associated with fungus-growing termites
Termitomyces spp. are the symbiotic fungus associated with the fungus-growing termites (Figure 2).
The fruiting body from the fungus in the fungus gardens appears above ground indicating the presence of a termite nest (Figure 3).
Fungi of Xylaria spp. are saprophytic fungi that grow on the rotten fungus gardens of deceased termite colonies. Their fruiting bodies also appear above ground (Figure 4) and indicate the location of a deceased colony (Figure 5).
Image credit: Images kindly provided by Dr. Jie-Hao Ou/National Chung Hsing University (Figures 2, 3 and 4) and Dr. Chun-I Chiu/Chiang Mai University (Figure 5).
Information on termite treatments.
1 Gordon, Johnalyn & Velenovsky, Joseph & Chouvenc, Thomas. (2022). Subterranean termite colony elimination can be achieved even when only a small proportion of foragers feed upon a CSI bait. Journal of Pest Science. 95. 1-10. 10.1007/s10340-021-01446-4.
2 Chouvenc, Thomas & Lee, Sang-Bin. (2021). Queen Egg Laying and Egg Hatching Abilities are Hindered in Subterranean Termite Colonies When Exposed to a Chitin Synthesis Inhibitor Bait Formulation. Journal of Economic Entomology. 114. 10.1093/jee/toab200.
3 Chouvenc, Thomas. (2021). Subterranean Termite (Coptotermes gestroi (Blattodea: Rhinotermitidae)) Colony Elimination Through Exposure to a Novaluron CSI Bait Formulation in Laboratory. Journal of economic entomology. 114. 10.1093/jee/toab061.
4 Iqbal, Naeem & Alvi, Abid & Hussain, Mujahid & Saeed, Shafqat & Naeem-Ullah, Unsar & Khan, Alamgir & Abid, Allah. (2020). Foraging behavior and bait station preference in scavenging termite, Odontotermes obesus (Blattodea: Termitidae). Bulletin of Entomological Research. 111. 1-9. 10.1017/S0007485320000693.
5 Chiu, Chun-I & Chuang, Ya-Hui & Liang, Wei-Ren & Yeh, Hsin-Ting & Yang, Hsiao-Ying & Tsai, Ming-Jer & Spomer, Neil & Li, Hou-Feng. (2021). Area-population control of fungus-growing termite, Odontotermes formosanus , using hexaflumuron durable baits. Pest Management Science. 78. 10.1002/ps.6612.
Termite Professional Australian edition, 2021
Do termites adjust their diet in response to macronutrients?
Termites may select food based on the quantity present, but do they vary their food intake to achieve a balanced diet? Nutritional ecology theory predicts that omnivores will vary their diet to achieve a balanced intake of nutrients, yet specialist feeders such as termites – which have evolved to feed on a narrow range of foods that match their dietary requirements – are unable to switch between different food types to maintain nutrient intake.
Researchers working with Nasutitermes exitiosus carried out a series of laboratory trials presenting groups of termites with paired food sources: one carbohydrate (cellulose) and one protein.1 Termites collected the same total amount of food irrespective of the foods presented, but took less of higher protein foods. As expected for a specialist feeder, termites did not adjust their diet to a specific carbohydrate to protein ratio. Unlike many ant species, which vary the level of protein in their diet depending on the amount of brood present, in this trial the presence of different castes (including larvae) did not impact intake or diet choice.
Do termites adjust their diet in response to micronutrients?
Foraging theory suggests that animals will preferably choose food that contains nutrients that are lacking in their diet. With termites feeding exclusively on cellulose material (wood and other plant material), their diet is typically lacking in protein and some micronutrients (vitamins and minerals). For example, the ash content of wood is between 0.2 to 2.1%, whereas the ash content of termites is between 3.72% and 9.9% depending on species. The main elements of ash are phosphorous, potassium, calcium and magnesium with a range of trace elements. With this in mind, Suhara (2020) investigated whether termites preferentially feed on food sources higher in these ash elements.2
Using filter paper disks dosed with one of the test solutions, covering a range of doses, the disks were then dried before being fed to groups of termites (workers and soldiers) collected from field colonies of Coptotermes formosanus. Trials were carried out in both multiple choice (1250 termites) and no-choice (100 termites) feeding situations.
In the multiple choice feeding situations, only one treatment – dipotassium phosphate – significantly increased consumption relative to the untreated control, actually increasing consumption by 2.5 times. However, in the no-choice study, the termites appeared to eat the same amount of paper disks, whether or not they contained dipotassium phosphate. It could be that although dipotassium phosphate is preferred to other food sources, it does not boost overall intake. The researcher suggested that the small number of workers used in the no-choice study may have influenced this result. Nevertheless, the conclusion was that dipotassium phosphate has the potential to increase bait palatability but that field trials with actual bait impregnated with dipotassium phosphate are necessary.
New potential bait actives?
Some pest managers swear that the addition of Gatorade – blue Gatorade to be precise – improves the ‘hit rate’ and palatability of termite baits. Certainly there is some evidence to suggest it can increase the rate of tunnelling in treated sand.3 But interestingly, the latest research indicates that erythritol, the sweetener used in many sugar-free soft drinks, actually appears to cause mortality in termites.4
Researchers at Drexel University in Philadelphia investigated whether erythritol – which is known to cause increased mortality when ingested by some insects – might have potential as a novel termite bait active. Workers of the eastern subterranean termite (Reticulitermes flavipes) were fed paper soaked in different concentrations of erythritol. The termite mortality measured at eight days after bait presentation was positively correlated with concentration, with the higher concentrations achieving over 80% mortality after eight days.
The termites consumed paper even with the highest level of erythritol and the researchers observed no avoidance behaviour in choice bioassays versus untreated paper, no matter the concentration of erythritol. As such, the researchers recommended that research should continue into the potential of erythritol as a termite bait active.
Whether or not erythritol sees the light of day as a commercial termite bait, these results highlight the risk of adding supplements with unknown properties to termite baits. Without testing, there is no way of knowing how even the most benign chemical may impact termite behaviour. It is for this reason that bait manufacturers generally test their bait products with distilled water, to avoid adding any impurities to the bait matrix. As always, there is a reason to follow the label.
New insecticides actives do not come along very often, so some termite researchers are taking a different approach. Since higher termites are very much reliant on their gut symbionts, which include a range of bacteria, it makes sense to see whether antibiotics could have a role in termite control.
After extracting gut bacteria from Microcerotermes diversus, the researchers screened a range of antibiotics on the cultivated bacteria.5 As a result, two antibiotics, chloramphenicol and nalidixic acid, were assessed for their impact on termite behaviour. When fed on wood treated with antibiotics, termites showed a significant reduction in health, as measured by reduced tunnelling and reduced running speed. However, the presence of the antibiotics did result in a reduction of the amount of wood consumed, potentially due to an adverse taste or smell, or potentially food aversion through a feedback mechanism.
Some interesting early results, but a lot more research is required to establish whether antibiotics have a role to play in termite control. It is certainly an area of interest, as control of higher termites such as Nasutitermes can be a lengthy process using traditional baits.
Only add bait to one in-ground station?
When attempting colony elimination with baiting it is best practice to add bait to all bait stations that have active termites and to keep replenishing with bait until the termites stop feeding. But is this really necessary? Researchers from the Universiti Sains Malaysia set out to see whether colony elimination could be achieved with greatly reduced bait usage.6
The researchers mapped out activity at six sites (five in Penang and one in Kedah) using a combination of in-ground and above-ground monitoring stations. To confirm they were only dealing with one nest at each site, and mapping its foraging territory, the researchers used a mark recapture technique whereby termites were captured at one bait station and fed filter paper to stain them blue. They were subsequently released and their presence in bait stations at the site recorded. All sites were confirmed to have one colony of Coptotermes gestroi.
The researchers added chlorfluazuron bait to only one of the in-ground stations and monitored activity in all the bait stations every two weeks until the colony had been eliminated. At each two-week inspection, the bait in the treated bait station was replenished if required. At all six sites, colony control was successfully achieved within 4 to 8.6 weeks using less than 300 g of bait.
With the time to elimination no slower than the traditional method of adding bait to all active stations, adopting this strategy would provide some savings in both time and bait use. However, the key issue is knowing that the termite activity in all stations is from the same colony. For the pest manager in the field, carrying out a mark recapture study is not really an option. In summary, it remains best practice to bait all active bait stations in case more than one colony is involved.
Can you eliminate termites from an area by baiting?
In-ground baiting systems are normally placed around the perimeter of a structure to intercept termite activity. The bait will then eliminate the attacking colony. However, it is more than likely that other termite colonies in the area will be attacking the home. Placement of additional bait stations in potential ‘hotspots’ around the property may pick up some of these additional colonies, but it represents a somewhat hit and miss approach. A group of US researchers decided to investigate whether baiting can be used to eliminate termites from an area and keep the area termite free.7
The study involved installing 100 in-ground monitoring stations at two sites, with five metres in between each station, covering an area of just over 2000 m2. At each site, half the area was wooded and half the area was pasture. Over a two-year period, the colonies and activity in the areas were mapped. After two years, a novaluron bait was added to the bait stations in the wooded area at site A. The use of monitoring stations without bait, as a control, continued at site B. Termite activity at both sites was recorded for a further 18 months.
Prior to treatment, the sites hosted between 8-14 colonies (or approximately 55-100 colonies per hectare) of Reticulitermes flavipes and Reticulitermes virginicus. Of the 11 active colonies present in the treatment area at the time of baiting, seven colonies were no longer active within two months after treatment. By the end of the study, some 18 months later, no activity was recorded in the treatment site. In contrast, of the 12 colonies identified at the control site before baiting commenced on the treatment site, seven were still active at the end of the study.
The researchers concluded that it is indeed possible for wide-area baiting to eliminate termites from an area and that the location can be kept termite free as long as bait is present. The use of long-lasting baits in conjunction with regular termite inspections would be the most efficient method of keeping the area termite free.
1 Poissonnier, L.-A., Simpson, S.J., Dussutour, A., Buhl, J., 2020. Regulation of macronutrient intake in termites: A dietary self-selection experiment. JOURNAL OF INSECT PHYSIOLOGY 120. https://doi.org/10.1016/j.jinsphys.2019.103983
2 Suhara, H., 2020. Using phosphate to increase feeding consumption in termite Coptotermes formosanus. JOURNAL OF WOOD SCIENCE 66. https://doi.org/10.1186/s10086-020-01932-w
3 Cornelius, M.L and Osbrink, W.L.A (2008). Effect of bait supplements on the feeding and tunnelling behavior of the Formosan subterranean termite (Isoptera: Rhinotermitidae). Sociobiology 51(2):497-511.
4 Caponera, V. et al (2019). Erythritol Ingestion Causes Concentration- Dependent Mortality in Eastern Subterranean Termites (Blattodea: Rhinotermitidae). Journal of Economic Entomology 113(1): 348–352.
5 Mousavi, S.Q., Bandani, A.R., Alaie, E., 2020. Combination of antibiotics and chitin synthesis inhibitors for the control of Microcerotermes diversus (Isoptera: Termitidae). JOURNAL OF ASIA-PACIFIC ENTOMOLOGY 23, 957–962. https://doi.org/10.1016/j.aspen.2020.08.001
6 Umar, W.A.S.W., Ab Majid, A.H., 2020. Efficacy of Minimum Application of Chlorfluazuron Baiting to Control Urban Subterranean Termite Populations of Coptotermes gestroi (Wasmann) (Blattodea: Rhinotermitidae). INSECTS 11. https://doi.org/10.3390/insects11090569
7 Shults, P., Richardson, S., Eyer, P.-A., Chura, M., Barreda, H., Davis, R.W., Vargo, E.L., 2021. Area-Wide Elimination of Subterranean Termite Colonies Using a Novaluron Bait. INSECTS 12. https://doi.org/10.3390/ insects12030192