A lethal compound against mosquito larvae

(SÃO PAULO) The anti-mosquito properties of thyme oil have been known for a long time. But a team of researchers exploited the power of this plant to attack mosquito larvae before they can spread, using another common ingredient.By using corn starch and thyme essential oil, Brazilian and American researchers have been able to develop a low-cost, biodegradable larviciding system that can kill mosquito larvae that transmit yellow fever.

The mosquito Aedes aegypti, which transmits Zika, dengue and chikungunya, as well as yellow fever, lays eggs on moist surfaces and in small bodies of stagnant water. This is usually found in and around the house as open bottles, old tires, uncovered water tanks and flowerpots.

Eggs can remain viable for more than a year in dry environments. However, in contact with water, they hatch quickly and become larvae that become adult mosquitoes after 15 days.

"As Brazil faces a serious crisis in mosquito-borne diseases, the development of a particle that eliminates mosquito larvae from A. aegypti using a raw material Plentiful, inexpensive and yet biodegradable like corn starch, is fantastic. "

Jamille Dombrowski, parasitologist, University of São Paulo

Attacking mosquitoes at the larval stage – when the insect is most vulnerable and not yet a potential vector – is considered essential to stop their proliferation.In order to kill mosquito larvae and prevent their proliferation in water reservoirs, researchers have developed a system based on the use of essential oils as natural larvicide. These oils are obtained from the thyme plant (Thymus vulgaris) and contains thymol, a biological active ingredient widely used as a pharmaceutical and therapeutic agent.

The use of essential oils as natural larvicide is not new, but its application is often limited because they do not dissolve well in water, do not degrade easily and evaporate when applied freely in water. the environment.

In a study published in the journal Industrial Crops & Products, the researchers explain that they have found a way to overcome these limitations, using a microencapsulation technique. They used cornstarch, an abundant, cheap and biodegradable raw material, to develop microcapsules as a container for the release of thyme oil in water.

In the study, the authors say they managed to manipulate these microcapsules to modulate the release of the oil. In this way, even if they are in a dry environment, the microcapsules remain inert and maintain the essential oil of encapsulated thyme.

As soon as it is exposed to water, the shell begins to swell and release the larvicide. After three days, when the eggs hatch and the larval stage begins, the capsules release thymol (the active substance) into the water.

Ana Silvia Prata, an engineer in chemistry at the Food Engineering School of the University of Campinas, and one of the authors of the study, said: "In doing so, we were able to get a capsule that behaves exactly like the eggs laid by the mosquito A. aegypti. "

"When they first come into contact with water, the shells release only 20% of the thyme oil," she explained. "In testing, by letting the material dry and then rehydrating it, we found that the particles could still release the larvicide normally. "

This means that the microcapsules could remain functional for about five rain cycles, releasing one-fifth of their contents at a time.

The researchers suggested that the public sector could produce the microcapsules containing the larvicide, then make them widely available and accessible, so that people can pour them to the accumulation points of the rainwater.

"Producing a kilo of these particles is expected to cost about R $ 30 (US $ 7.24, about CFAF 4.322)," Prata said. "We are in talks with the private sector to find out if it can produce and distribute these products. "

Jamille Dombrowski, a parasitologist at the Institute of Biomedical Sciences at the University of Sao Paulo, who did not participate in the study, says the results deserve special attention from the government for a number of reasons.

"Given that Brazil is facing a serious crisis with regard to mosquito-borne diseases, the development of a particle that eliminates mosquito larvae from A. aegypti using an abundant, inexpensive and yet biodegradable raw material like corn starch is fantastic, "she told SciDev.Net.

"In addition, thyme essential oil is a completely biodegradable material that is easy to obtain and poses no risk to human health. "