Leaf extracts of the plants `leucas aspera' and `ocimum sanctum' or tulsi have been found to be highly toxic to mosquito larvae and have a deterrent effect against the adult mosquito anopheles stephensi which spreads malaria.The tulsi extracts are also easy to handle, inexpensive and safe natural products for mosquito control, researchers from the Bharathiar University in Coimbatore say.

Writing in the journal Current Science, K Murugan and D Jeyabalan report that extracts of tulsi, wheat (triticum aestivum) and neem (azadirachta indica) can be used to disinfect water containing larvae. The scientists screened the effects of extracts of leucas aspera, ocimum sanctum, azadirachta indica, allium sativum, and curcuma longa (turmeric) on various stages of mosquito growth larvae, pupa and adults at concentrations varying from 1.0 to4.0 per cent. The anopheles stephensi breeds in wells, overhead or ground-level water tanks, cisterns, coolers, roof gutters and artificial containers.

It is found to be responsible for almost half of the annual malaria cases and transmits the disease in the plains of rural and urban India.The extracts of tulsi, wheat and neem can also be used for disinfecting water, it says, adding tulsi leaf extracts can be used in water tanks. to suppress anopheles stephensi.

The team found that leaf extracts of leucas aspera, tulsi and neem, as well as the pulp of allium sativum and rhizome of turmeric, killed mosquito larvae. Of these, leaf extracts of leucas and ocimum were the most effective.At four per cent concentration, leucas extract killed 90 per cent of the larvae, while tulsi or ocimum killed 84 per cent of the larvae.

The extracts also inhibited egg-laying by female mosquitoes, leading to fewer larvae. Extracts of all five plants are potential repellents against anopheles stephensi, the report in CurrentScience says.