The Indian team of Dr Musharrah A. Ansari, Senior Deputy Director (Entomology), Malaria Research Centre, and Padma Vasudevan of the Centre for Rural Development, Indian Institute of Technology, Delhi, found that the oil of the locally-grown Mentha piperita (peppermint) not only repels mosquitoes but also kills their larvae.

The research was part of an ongoing effort to look for safe alternatives to commercial repellents. Peppermint oil was evaluated on its ability to kill larvae and adult mosquitoes, as well as an effective repellent. Over 80 per cent of India's population is at risk from malaria, which kills one million people globally.

``We found that even sub-lethal doses of the oil in water containing larvae inhibited the longevity, fecundity and fertility of the adults that emerged from the larvae,'' Dr Ansari told Express Newsline.

This means that peppermint oil available for about Rs 200-Rs 250 a litre -- can be used both as a mosquito repellent and as a natural insecticide for killing larvae. ``As little as 1 ml of pure peppermint oil applied on the exposed parts of the body can repel mosquitoes for up to 8-10 hours,'' says Dr Ansari. The protection offered by the oil varied between different mosquito species, it averaged 85 per cent. ``The good news is that the oil was particularly effective against Anopheles culicifacies, which isresponsible for three-quarters of malaria transmissions in north India,'' says Dr Ansari.

Its insecticide properties were also tested on the larvae of three mosquito species Aedes aegypti (which spreads dengue fever), Anopheles stephensi (malaria) and Culex quinquefasciatus (filaria and West Nile virus). The oil was added to water in trays containing larvae. When the concentration of oil reached 3 ml/sq m of water, all the C. quinquefasciatus larvae died within a day, along with 90 per cent of A. aegypti and 85 per cent of A. stephensi. ``Higher concentrations of the oil would kill all the larvae,'' says Dr Ansari.

While some scientists caution that too much oil would be needed for it to be a viable alternative to more potent commercial insecticides, Dr Ansari remains upbeat. ``It could be a completely natural replacement for synthetic compounds in use in the form of coils, liquidifiers and mats,'' he says.The vapours of these chemical repellents, when inhaled over a period of time, are known to aggravate breathing disorders such as asthma, especially in infants and children. Peppermint oil could well sound the death toll for the Rs 100-crore commercial repellent market.

Already in use in the pharmaceutical and confectionery industry, peppermint oil is non-toxic for humans, which makes it completely safe for application. It is completely natural and is traditionally extracted through steam distillation of mentha leaves.