Termite Repellents

Scientists are continually testing new compounds in a bid to find a chemical with termite repellent properties. Here, we outline the latest developments in this field.

Latest termiticide and termite repellent research

Can termites warn nestmates about insecticide presence?

Although ants emit alarm pheromones, alarm communication in termites is primarily through vibroacoustic signalling – through drumming (head banging) and body shaking.

It is not only when disturbed or threatened by a predator or competitor that termites exhibit such alarm signals; recent research has demonstrated that Reticulitermes flavipes exhibited shaking alarm behaviour after workers were exposed to fungal spores from Metarhizium
brunneum
and M. robertsii. This raised the question as to whether termites also demonstrated alarm behaviour when exposed to the threat of an insecticide?

Researchers exposed workers of Nasutitermes corniger to a sub-lethal dose of imidacloprid.1 The results demonstrated that workers exposed to imidacloprid did indeed show shaking alarm behaviour and that the shaking behaviour increased with increasing doses of imidacloprid. The authors believe that these results demonstrate the existence of an “insecticide alert behaviour” which would essentially allow affected termites to communicate the potential threat to the colony.

The authors believe this opens up new perspectives on termite behaviour and has a potential impact on termite management studies. However, this behaviour has not been investigated in other species to date.

In a separate study, again on Nasutitermes corniger, the presence of soldiers in a group significantly increased the duration of survival of groups of termites exposed to insecticide.2 The researchers hypothesised that this could be due to the vibratory alarm behaviour or possibly
due to enzymes produced by the soldier caste having an increased capability of detoxifying insecticides.


Soldiers of Nasutitermes corniger exhibit shaking alarm behaviour when exposed to pathogenic fungi and insecticides (photo credit: Bernard Dupont/Wikimedia Commons)

Is insecticide resistance in termites possible?

Insecticide resistance is a key issue in agriculture and is becoming an increasing issue in some aspects of urban pest management, in particular with bed bugs, flies, mosquitoes, German cockroaches and rodents. It is therefore not surprising that pest managers will question
the possibility of insecticide resistance when a treatment appears to underperform. Whilst it may be a possibility with the pests listed above, is insecticide resistance really possible in social insects, such as termites?

Leading global urban entomologists Prof. Michael Scharf (University of Florida) and Prof. Chow-Yang Lee (University of California, Riverside) have reviewed the evidence from honeybees, ants and termites, in their recent review article on this topic.3

Crucial differences exist in the population structure and reproduction strategies of eusocial insects (bees, ants, termites) compared to non-social insects (bed bugs, cockroaches, flies, mosquitoes).

All the adults in non-social insects can reproduce and their reproductive rate can be rapid. As a result, the population can quickly respond to selection pressures. For example, if a few resistant adults remain after a treatment, they can rapidly breed, passing on their resistant genes to the next generation. Repeated exposure to the same insecticide will favour the more resistant individuals and thus a strongly resistant population can quickly develop.

For eusocial insects the situation is quite different, and their population dynamics provide a barrier to the natural selection pressures that drive insecticide resistance. In termite colonies, the vast majority of individuals are non-reproductives, which means they cannot pass on their genes to the next generation. When a treatment takes place, it is often targeted at a single colony, often with a single reproductive (if present, any secondary reproductives will likely have the same genetics). As a result, there aren’t the number of reproductives nor the variation in genetics to drive the development of insecticide resistance in the same way that would occur with an insecticide treatment on a cockroach population. Lastly, although termites produce a lot of reproductives, in many cases they only do so once a year – not the fast reproduction rate that allows for the development of insecticide resistance.

That’s not to say insecticide resistance couldn’t develop in eusocial insects. Firstly, natural variation in susceptibility to insecticides has been recorded in bees, ants and termites. Secondly, termites contain the same number of detox-encoding genes as the nonsocial insects, which do exhibit resistance. However, the insecticide pressure needs to be applied over a larger area over a longer period of time for the selection
pressure to drive the development of resistance.

The researchers conclude that our current understanding indicates that although metabolic insecticide resistance in ant and termite populations is a theoretical possibility, there is little evidence to confirm insecticide resistance in field populations. So, if pest managers have any issue with the efficacy of a treatment, it will probably be due to an issue with application, a quality issue with the product, or not fully understanding the termite situation at the property, rather than a case of insecticide resistance.

When it comes to studies on termites, the authors also pointed out that the gut symbionts should be part of any investigations. Not only are they metabolically active, but they also have rapid reproductive cycles, allowing for the quick selection of beneficial traits.

Can termite gut symbionts provide termites with insecticide resistance?

Termite gut symbionts not only aid termites with cellulose digestion but also confer a number of other fitness benefits. Recent research has linked various bacterial symbionts to reduced insecticide efficacy in a range of insects. The question is, could bacteria also provide termites with tolerance to insecticides?

Researchers undertook a series of experiments using the gut symbionts from Reticulitermes flavipes, growing them in media dosed with imidacloprid.4 The initial cultures allowed the researchers to identify one isolate (found to be a Chryseobacterium) that had a natural tolerance to imidacloprid. Over the next ten days, the isolates were sub-cultured every 12 hours. After ten days of constant exposure to imidacloprid, the insecticide tolerance had increased significantly (up to five times). With the isolate doubling every 38 minutes, over the course of the ten-day trial, the bacteria would have gone through >300 generations to develop this increased tolerance.

Chryseobacterium
Gut symbionts (such as this Chryseobacterium) may have the potential to increase insecticide resistance in termites (photo credit: Dukas.ju, CC BY-SA 4.0)

Whilst insecticide resistance in the termites themselves is unlikely to occur – or would take a very long time to develop due to their reproduction strategy and life cycle – clearly insecticide resistance could develop quite quickly in their gut bacteria. If bacteria develop traits
to neutralise insecticides, then it would clearly result in termites with increased insecticide tolerance. With termites exhibiting proctodeal trophallaxis, resistant bacteria could easily be passed between nestmates and also from reproductives to their new offspring after colony founding.

References

1 De Mendonça, T.H.C et al. (2023). How to perceive the insecticide? The Neotropical termite Nasutitermes corniger (Termitidae: Nasutitermitinae) triggers alert behavior after exposure to imidacloprid. Behavioural Processes, 209: https://doi.org/10.1016/j.beproc.2023.104887

2 Watanabe, S.Y.M. et al. (2023). It is not only group size: Soldiers also modulate the tolerance to insecticide in termites (Blattodea: Isoptera).
Entomological Science, 26(2). E12546. https://doi.org/10.1111/ens.12546

3 Scharf, M.E and Lee, C-Y (2024). Insecticide resistance in social insects: assumptions, realities, and possibilities. Current Opinion in Insect Science, https://doi.org/10.1016/j.cois.2024.101161

4 Blanton, A.G et al. (2023). In vitro assays reveal inherently insecticide-tolerant termite symbionts. Front. Physiol., 12 July 2023 Sec. Invertebrate Physiology: 14. https://doi.org/10.3389/fphys.2023.1134936

Termiticide and termite repellent research papers 2023

RNAi for termite control

This technology may be a long way off for termite control and may never happen, but it’s certainly an interesting area of research. RNAi stands for RNA interference and is a cellular process by which messenger RNA degradation and interruption of protein synthesis turn off gene function. It can be used to develop technology to target specific genes in insects resulting in the desired pest control effects. For example, transgenic RNAi plants have been created to provide protection against plant-feeding pests.

There are four key challenges with this technology. Firstly it is necessary to fully map the target pest genome, metagenome and transcriptome sequences to develop the necessary RNAi technology. Secondly, a vehicle needs to be developed to deliver the RNAi insecticide into the insect. Thirdly, although the technology will certainly deliver control of individual insects, it is unclear as to how it would control a whole colony. And lastly, any environmental impact needs to be carefully considered.

For termite control, work is underway to address all of these challenges to determine the potential for RNAi termiticides. Recent research has determined that termites do indeed have the RNAi machinery core genes to enable this technology to be effective. The mapping of termite genomes is currently underway by various research groups.1 One challenge in delivering dsRNA (the RNAi bioactive molecules) into termites is that it appears that the termite gut and possibly some of their gut symbionts produce enzymes which breakdown the dsRNA. However, this latest research has produced data to show that the use of chitosan nanoparticles appeared to protect the dsRNA from enzymic breakdown in the termite gut. Termite specific viruses also have potential to target RNAi and the feasibility in using viruses in this way has been confirmed in other insects. However, this control route, which would involve releasing recombinant viruses into the environment would need close evaluation from an environmental point of view.

Evaluation of cycloxaprid termiticide

Cycloxaprid is a new neonicotinoid insecticide and has received interest due to its novel structure compared to other neonicotinoids: it has an NO2 group in a cisconfiguration as opposed to the trans-configuration of other neonicotinoids.

A recent study evaluated its efficacy on Coptotermes formosanus in comparison to fipronil.2 Its efficacy was evaluated in exposure studies (to treated sand and soil), no-choice tunnelling bioassays (to see how far termites would tunnel in treated soil), choice bioassays to determine level of repellency, and horizontal transfer bioassays. The results showed that cycloxaprid was slightly less toxic to termites than fipronil, which means a higher concentration was required to deliver the same level of mortality. Cycloxaprid demonstrated both delayed mortality and transfer effects.

Cycloxaprid
Cycloxaprid, a novel neonicotinoid

 

Interestingly, cycloxaprid was non-repellent at lower concentrations but appeared to show repellency at higher concentrations. Fipronil was also non-repellent at the low concentrations, although it was not possible to assess repellency at the higher concentrations due to the rapid termite mortality. Both insecticides resulted in reduced tunnelling in both soil and sand substrates at all concentrations tested. Although there were differences in performance between cycloxaprid and fipronil, the researchers concluded cycloxaprid had potential as a liquid termiticide. It remains to be seen if it will be commercialised.

Broflanilide as a new termiticide

Broflanilide is a meta-diamide insecticide discovered by Mitsui Chemicals Agro, branded Tenebenal. It has been co-developed by BASF. Broflanilide belongs to a new group of insecticides, Group 30, GABA-gated chloride channel allosteric modulators. Broflanilide is a broadspectrum insecticide effective on a wide range of crop and public health pests. With its novel mode of action, it could prove particularly useful in controlling mosquitoes, cockroaches and bed bugs, insects with known resistance to other groups of insecticide. It has both direct spray efficacy and long residual performance on surfaces.

 

Broflanilide
Broflanilide, a new insecticide with a novel mode of action

 

Evaluations of broflanilide on termites have commenced. Working with Reticulitermes flavipes in the laboratory, broflanilide impacted survival rate and food consumption at very low concentrations, also impacting a range of other behaviours.3 It also showed no repellency effects up to 32 ppm and delayed mortality, with termites taking up to three days to die after one hour of exposure. The researchers concluded that broflanilide had potential as a termiticide and more testing is required.

References

1 Mogilicherla, Kanakachari & Chakraborty, Amrita & Taning, Clauvis & Smagghe, Guy & Roy, Amit. (2022). RNAi in termites (Isoptera): current status and prospects for pest management. Entomologia Generalis. 43. 10.1127/entomologia/2022/1636.

2 Zhang, Lang & Zhang, Jianlong & Wang, Changlu & He, Yinghao & Wen, Xiujun & Xu, Zhiping & Wang, Cai. (2022). Toxicological, Behavioral, and Horizontal Transfer Effects of Cycloxaprid Against Formosan Subterranean Termites (Blattodea Rhinotermitidae). Journal of Economic Entomology. 115. 10.1093/jee/toac073.s

3 Zhou, Jiachang & Liu, Shiying & Yin, Yuting & Jia, Bao & Zhang, Daoxiong & Li, Ganghua. (2022). Multifaceted evaluation of tenebenal as a new termite insecticide. International Journal of Tropical Insect Science. 42. 10.1007/ s42690-022-00905-4. 

Termiticide and termite repellent research papers 2022

New materials with termite activity

Chemicals and materials that repel termites, instead of or in addition to killing termites, are a focus of research and evaluation.

Researchers in the US have taken a closer look at menadione (vitamin K3), which is known to have toxic effects on some insects, although its impact on termites is unknown. It is of particular interest due to its low mammalian toxicity. Working on Coptotermes formosanus, the researchers evaluated the effects of menadione on foraging behaviour and mortality.1

In comparison to fipronil, menadione delivered lower mortality at the same concentration (0.6 μg/μL), but was just as effective in reducing feeding (filter paper consumption). However, in no-choice trials menadione delivered comparable levels of mortality. The researchers concluded that although menadione does deliver mortality at low concentration levels (with a mode of action similar to chlorfenapyr), it is its repellent properties that are likely to provide more potential benefit in termite management. So rather than investigating its potential as a soil treatment, further trials should look at its use in wood preservation and potentially in the direct treatment of termites in active infestations.

Biochar (pictured above) has received a lot of attention as a result of its potential to mitigate greenhouse gas emissions. Burning and natural decomposition of trees and agricultural matter releases large amounts of carbon dioxide into the atmosphere. If the same materials undergo a slow pyrolysis process (heating in the absence of oxygen), a carbon-rich charcoal (biochar) is produced. This can sequester the carbon for up to 5000 years. As such, the potential uses of biochar are being investigated for soil improvement and fertility. As a consequence, it is being evaluated for its impact on soil arthropods. A recent study investigated its impact on Coptotermes formosanus.2

The study demonstrated that concentrations of biochar in the soil of >5% repelled the termites and started to impact their survival. At these levels, the soil pH increased and the soil moisture decreased. In addition, when higher levels of biochar were added (>20%) the soil bacteria composition was altered and the abundance of pathogens deleterious to termites also increased. The researchers concluded that soil that has been altered to include biochar at levels of >10% has the potential for use in termite management and should be investigated further.


References

1 Ngo, Kieu & Castillo, Paula & Laine, Roger A & Sun, Qian. (2021). Effects of Menadione on Survival, Feeding, and Tunneling Activity of the Formosan Subterranean Termite. Insects. 12. 1109. 10.3390/ insects12121109.

2 Chen, Yong & Zhao, Chongwen & Zhang, Dandan & Zhang, Shijun & Zeng, Wenhui & Li, Zhi-Qiang. (2022). The effect of amending soils with biochar on the microhabitat preferences of Coptotermes formosanus (Blattodea: Rhinotermitidae). Ecotoxicology and Environmental Safety. 232. 113240. 10.1016/j.ecoenv.2022.113240.

Further reading:

General information on termites

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