Tackling mosquito menace: Natural pesticide vs chemical solutions

Chennai: While entomologists and doctors are increasingly worried about entomological changes in mosquitoes and experts opine that the dengue-causing vectors have gained resistance to temephos, a larvicide sprayed across the State to kill the insect, the government continues to bet on old solutions.

In search of answers for pertinent questions, News Today speaks to a few experts in the city to explore several facets surrounding the chemicals used for fogging.

Alarmed by the widespread attack of dengue, a study carried out by Loyola College Entomology Research Institute (ERI) proved that there has been a rampant invasion of Aedes aegypti mosquitoes in several districts in Tamilnadu.

Following the study, ERI former director, Father Dr S Ignacimuthu, and research scholar Rajan Maheswaran proposed an alternative – natural pesticide ‘Ponneem’ – to check the breeding of Aedes aegypti and Aedes albopictus mosquitoes a few years ago.

Speaking about the novel herbal formulation, Fr Ignacimuthu said, “As Ponneem is purely based on natural components, it contains thousands of compounds that would take several generations for the mosquito to break.”

The paper, presented by Fr Ignacimuthu and Rajan Maheswaran, cited that the new substance was prepared using the oil of neem, karanj or pungai and their extracts. The mixture was tested for larvicidal, ovicidal and oviposition deterrent activities against Aedes aegypti and Aedes albopictus species.
The results revealed that the natural remedy showed 100 per cent results under laboratory and sunlight-exposed conditions up to 12 months.

The study said the presence of several plant molecules has made the compound effective in battling the growing mosquito menace in the State.

AT PRESENT

Even as the government continues to use temephos, a former chief entomologist opines that the formula is efficient if used in the right proportion.

Elaborating, Directorate of Public Health and Preventive Medicine former chief entomologist M S Mohideen Abdul Kader said, “Temephos is used by mixing the larvicide with water in the ratio of 2 ml:1 litre. The mixture is then further sprayed to the freshwater in equal amount. If not used in the right quantity, 100 per cent results will not be achieved. The mosquitoes that survive will have the capacity to develop resistance that will be passed on to generations through the gene.”

People from the interior regions are well-aware of the precautionary measures to prevent the proliferation of the species. He also stated that the villagers use chlorine to disinfect containers used to store water and temephos is judiciously used when required.

“The bleaching powder destroys the larvae and its food completely. The Aedes mosquito does not lay eggs in chlorinated water due to the smell. Even if the eggs are found in the water, chlorinated water does not help in the growth of larvae,” he added.

Despite this, the preliminary report submitted by the Tamilnadu Department of Health and Family Welfare to the Madurai bench of the Madras High Court on Tuesday stated that 3,440 had contracted dengue in the State and 13 succumbed to it.

NEW SUBSTANCE?

When asked if the government was working on a new formula to control the breeding of Aedes species, Mohideen said, “As of now, only temephos is widely used to kill the Aedes mosquito. There is also another substance called Diflubenzuron which is used in Delhi. I presume the State government would start using the new substance.”

Bhavani Prabhakar