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(Pictured: The lower leg of a mosquito after contact with volcanic rock powder. Statically transferred perlite particles dehydrate mosquitoes, killing them. Photo courtesy of Jean Deguenon, NC State University.)

An indoor residual spray made by combining a type of volcanic glass with water has shown effective control of mosquitoes carrying malaria, according to a new study. The results could be useful in reducing populations of disease-carrying mosquitoes – and the risk of malaria – in Africa.

Malaria, an infectious disease transmitted by mosquitoes, kills some 400,000 people in Africa each year. The use of insecticide-treated mosquito nets and indoor residual sprays are the most common and effective methods of reducing mosquito populations in Africa. But mosquitoes are becoming increasingly resistant to commonly used insecticides such as pyrethroids, so it is important to use safe alternative chemistry to control mosquitoes.

The volcanic glass material used in this new intervention is perlite, an industrial mineral most frequently used in building materials and in gardens as a soil additive. The tested insecticide created from perlite, called Imergard WP, ​​can be applied to interior walls and ceilings – and possibly even the interior of roofs – as a residual spray indoors. The spray contains no additional chemicals, is not toxic to mammals and will be cost effective. The first results show that mosquitoes do not seem to have resistance to spraying perlite.

In the study, entomologists at North Carolina State University worked with the Innovative Vector Control Consortium (IVCC) based at the Liverpool School of Tropical Medicine and Imerys Filtration Minerals Inc. to test Imergard WP. Researchers used the spray in experimental huts in the Republic of Benin (West Africa) to test the effects of the spray on wild and more susceptible strains of Anopheles gambiae mosquitoes, the main vector of malaria in sub-Saharan Africa.

Researchers used four different tests to verify the effectiveness of Imergard WP. The huts in the control study did not have mosquito spray. In the second group, the walls of the huts were covered with a common pyrethroid. The walls of the huts were sprayed with Imergard WP in the third group, while in the fourth group, the walls of the huts were sprayed with a mixture of Imergard WP and common pyrethroid.

Huts with walls treated with Imergard WP, ​​with and without pyrethroid, showed the highest mosquito mortality rates. The results showed that the mortality rates of mosquitoes landing on walls treated with Imergard WP were over 80% up to five months after treatment, and over 78% at six months. Treatments have been effective against susceptible and wild-type mosquitoes.

“The statically transferred perlite particles essentially dehydrate the mosquito,” said Mike Roe, William Neal Reynolds professor emeritus of entomology at NC State and corresponding author of the article. “Many die within hours of contact with the treated surface. Mosquitoes are not repelled by a treated surface because there is no olfactory mechanism to smell the rock.

Huts sprayed with only the common pesticide had mosquito mortality rates of about 40-45% over five months, with rates dropping to 25% by month six of the study.

“The treatment of perlite as an insecticide is new,” said David Stewart, director of business development for Imerys, the company that created Imergard WP, ​​and co-author of the article. “This material is not a silver bullet, but a new tool that can be seen as part of an insect vector management program.”

The study was published in the journal Insects. NC State postdoctoral researcher Jean M. Deguenon from Benin and a Fulbright alumnus in Roe’s lab is the first author of the article. Co-authors of the study include Charles S. Apperson of NC State; Marian McCord, now at the University of New Hampshire; Roseric Azondekon, Fiacre R. Agossa, Gil G. Padonou, Rodrigue Anagonou, Juniace Ahoga, Boris N’dombidje, Bruno Akinro and Martin C. Akogbeto from the Center for Entomological Research of Cotonou, Benin; and Bo Wang, David Gittins and Larissa Tihomirov from Imerys.

The study was funded by Imerys and the Deployed War-Fighter Protection Program of the US Department of Defense (grant W911QY191003). All opinions, findings and conclusions or recommendations expressed in this document are those of the authors and do not necessarily reflect the position or policy of the government and no official endorsement should be inferred.

Source: North Carolina State University


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