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
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.
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.
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.
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.
Termite Professional Australian edition, 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.
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.