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Scientists have developed an improved method for controlling container-inhabiting mosquitoes responsible for the transmission of chikungunya and dengue viruses.

New pellet formulations of a chemical that kills mosquito larvae and pupae — Agnique — were used for the first time in combination with another insecticide — Altosid — in laboratory and field tests.  Combined, the two insecticides had a longer-lasting effect than using either one alone.

They were used in a spray to coat water-filled containers where mosquitoes deposit their eggs.

In the laboratory, this provided 80 per cent mosquito control for 60 days, and 95 per cent control for at least 32 days in the field trials, according to the study published in this month's (May) issue of The American Journal of Tropical Medicine and Hygiene.

The spray's dual action interfered with mosquitoes' development as well as the surface tension of the water — preventing larvae and pupae from remaining on the surface to breathe.

Altosid also remained effective after 107 days of a drought simulated in the laboratory, suggesting that it could prevent mosquitoes breeding even when dried-out water containers are refilled after periods of drought.

Co-author of the study Banugopan Kesavaraju, entomologist at US-based Salt Lake City Mosquito Abatement District, told SciDev.Net that "the container mosquitoes like Asian tiger mosquitoes, Aedes albopictus, colonise containers that can hold small quantities of water such as trash cans, cemetery vases and toys, which are more common in urban and suburban areas".

He said that this makes the use of pesticides difficult in urban areas. Since the combined spray targets all mosquito life stages in the containers, this would permit better long-term mosquito control, he added.

Nuananong Jirakanjanakit, biomedical researcher at Mahidol University, Thailand, said this new method could be a realistic way of tackling mosquitoes and capping the transmission of diseases such as chikungunya and dengue fever.

Chikungunya virus is spread by mosquitoes found in standing water in urban areas. It re-emerged on several islands in the Indian Ocean in 2005, caused an outbreak in India in 2006–07, and was reported in Europe in 2007.

Dengue is now the most rapidly spreading mosquito-borne viral disease in the world (see also Dengue fever surges in Americas). In the absence of an effective drug or vaccine, vector control is the only way to reduce disease transmission.

Theeraphap Chareonviriyaphap, entomologist at Thailand-based Kasetsart University, welcomed the new development as "a major breakthrough in the battle against dengue and chikungunya viruses". He told Scidev.Net that this is "a very simple combination but with a powerful effect on the ground leading to the killing of most vectors hidden in the containers".

But Michael Turell, medical entomologist at USArmy Medical Research Institute of Infectious Diseases told SciDev.Net that educating people about how discarded trash provides breeding ground for disease-carrying mosquitoes could be as important as improving insecticides. "If these [trash cans] were turned upside down so that they would not hold water, I think it would have an even greater effect than a more efficient formulation of insecticides."

Link to article abstract in The American Journal of Tropical Medicine and Hygiene

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