The resinous substances gathered by bees is the latest natural compound to exhibit promising termiticidal properties.
Researchers are constantly screening new chemicals for their insecticidal properties, with the natural world a wealthy source of unique compounds. Propolis or ‘bee glue’ is the latest material under investigation.
Bee glue is the collective name for the resinous substances collected from various plants and is generally used by bees as a construction material for their hives. It hardens cell walls, it is used to seal holes and repair cracks, and is applied to smooth the inner surface of the hive. It also has insulation properties. However, its interest to humans arose from its apparent antiseptic properties and indeed is attributed as a key factor in keeping the hive disease free. As a result, numerous scientific investigations have been evaluating propolis and its extracts for various medicinal properties, not only as an antiseptic, but for its potential as an anti-bacterial, anti-fungal, anti-inflammatory and even anti-cancer treatment. As with any chemical that has potential biocidal properties, it’s not long before its insecticidal properties are investigated.
Researchers from the Universiti Sains Malaysia have evaluated propolis for its repellency and insecticidal properties on termites. Using propolis collected by the stingless bee, Heterotrigona itama, its potential as a repellent and contact insecticide was evaluated against the termite Coptotermes curvignathus.
To assess its repellency, a powdered extract of propolis was diluted with ethanol to create three concentrations (10%, 20% and 30%). In each trial one of the solutions was applied to one half of a filter paper ‘arena’, with the other half of the arena treated with ethanol alone. The number of termites found on each half of the filter paper was evaluated after one hour. The researchers found there was increasing repellency with increasing concentration of propolis, with 70% repellency achieved with a 30% solution of propolis.
The same solutions were assessed for their contact toxicity. Termites were briefly dipped in each solution (with ethanol alone as a control), and mortality measured over a three-hour period. Again, increasing mortality was observed with increasing concentrations of propolis with 100% mortality achieved within three hours for the highest concentration. Probit analysis provided an LC50 of 15.9% (w/v) with an LT50 of 1.5 hours. As the propolis was demonstrated to be toxic to the termites, the avoidance observed in the repellency trial was assumed to be due to the presence of toxic compounds.
Interestingly, propolis also appears to inhibit the action of cellulase, produced by gut symbionts, which is used by termites to digest wood.
The researchers concluded that propolis has various mode of activity that could be utilised in the control of termites. Propolis contains a range of bioactive compounds such as phenolics and flavonoids, so deeper investigation will be required to fully understand propolis and which components may be providing the insecticidal activity. Even if termiticidal activity is proven, the route to commercialisation is often challenging – is it even possible to harvest enough propolis of a consistent specification to be commercially viable or is it better to focus on synthesising only the bioactive components?
Further reading: Zakeri, H.A. and Azmi, W.A. (2021). Prospect of propolis from stingless bee, Heterotrigona itama as biological control of the subterranean termite, Coptotermes curvignathus. IOP Conference Series: Earth and Environmental Science. 711. 012018. 10.1088/1755-1315/711/1/012018.