An indoor residual spray made by combining a type of volcanic glass with water showed effective control of mosquitos, which transmit malaria, according to a new study. The results could be useful in reducing disease-causing mosquito populations – and the risk of malaria – in Africa.
Malaria, a mosquito-borne infectious disease, kills around 400,000 people in Africa every year. Using insecticide-treated bed nets and residual sprays indoors is the most common and effective method of reducing mosquito populations in Africa. However, mosquitoes are becoming increasingly resistant to the commonly used insecticides such as pyrethroids. Hence, the need for alternative safe chemistry to control mosquitoes is important.
The volcanic glass material used in this new intervention is perlite, an industrial mineral most commonly used as a soil additive in building materials and gardens. The tested perlite insecticide called Imergard WP can be applied as a residual spray indoors on walls and ceilings – and possibly even on roofs. The spray does not contain any additional chemicals, is non-toxic to mammals and is inexpensive. First results show that mosquitoes do not seem to have any resistance to the perlite spray.
In the study, North Carolina State University entomologists worked with the Innovative Vector Control Consortium (IVCC) 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 spray’s effects on wild and more vulnerable strains of Anopheles gambiae mosquitoes, the primary malaria vector in sub-Saharan Africa.
The researchers used four different tests to check the effectiveness of Imergard WP. Control study huts did not have mosquito repellent spray. In the second group, the hut walls were coated with a common pyrethroid. In the third group, hut walls were sprayed with Imergard WP, while in the fourth group hut walls were sprayed with a mixture of Imergard WP and the common pyrethroid.
Huts with walls treated with Imergard WP with and without pyrethroid showed the highest mosquito mortality rates. The results showed that the death rate of mosquitoes landing on walls treated with Imergard WP was greater than 80% up to five months after treatment and 78% after six months. The treatments were effective against both susceptible and wild-type mosquitoes.
“The statically transmitted pearlite particles essentially dehydrate the mosquito,” said Mike Roe, William Neal Reynolds Distinguished Professor of Entomology at NC State and the corresponding author of the paper. “Many die within a few hours of contact with the treated surface. Mosquitoes are not repelled by a treated surface because there is no olfactory mechanism to smell stones. “
Cabins sprayed only with the usual pesticide had a mosquito mortality rate of around 40 to 45% over five months, with that rate dropping to 25% by the sixth month of the study.
“Processing perlite as an insecticide is new,” said David Stewart, commercial development manager at Imerys, the company that founded Imergard WP, and co-author of the paper. “This material is not a silver bullet, but a new tool that can be viewed as part of an insect vector management program.”
The study was published in the journal Insects. NC state postdoctoral fellow Jean M. Deguenon from Benin and a Fulbright alumnus in Roe’s laboratory is the lead author of the work. Study co-authors 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 de Recherche Entomologique de Cotonou, Benin; and Bo Wang, David Gittins and Larissa Tihomirov from Imerys.
The study was funded by Imerys and the Department of Defense’s Deployed War-Fighter Protection Program (Grant W911QY1910003). All opinions, results, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the position or policies of the government and no official endorsement should be made.
Note to editors: The following is a summary of the paper.
ImergardTMWP: A non-chemical alternative to a residual spray indoors that is effective against pyrethroid-resistant Anopheles gambiae (sl) in Africa
Authors: Jean M. Deguenon, Charles S. Apperson, Marian G. McCord, and R. Michael Roe, NC State University; Roseric Azondekon, Fiacre R. Agossa, Gil G. Padonou, Rodrigue Anagonou, Juniace Ahoga, Boris N’dombidje, Bruno Akinro and Martin C. Akogbeto, Center for Entomological Research of Cotonou; and David A. Stewart, Bo Wang, David Gittins, Larissa Tihomirov, Imerys.
Posted: May 23, 2020 in Insects
DOI: 10.3390 / insects11050322
abstract: Malaria is the deadliest mosquito-borne disease, killing mostly people in sub-Saharan Africa (SSA). The meanwhile widespread resistance of mosquitoes to pyrethroids and the rapidly growing resistance to other classes of insecticide recommended by the World Health Organization (WHO) could destroy the successes achieved in mosquito control in recent years. It is of the utmost importance to look for new, inexpensive and safe alternatives with new mechanisms of action that could improve the effectiveness of current insecticides. The effectiveness of a novel mechanical insecticidal mineral from volcanic rock, ImergardTM WP, was investigated to determine its effectiveness as a stand-alone residual wall spray and as a mixture with Deltamethrin (K-Othrine® Polyzone) in experimental huts in Cove, Benin. The assessment was carried out with susceptible (Kisumu) and wild-type Anopheles gambiae (sl). Deltamethrin used alone showed a mortality of 40–45% (72 hours after exposure) in the first four months, which decreased to 25% after six months in the wild. Gambiae from Cove. ImergardTMWP alone and mixed with Deltamethrin under the same test conditions resulted in mortality rates of 79–82% and 73–81%, respectively, over the same six month period. ImergardTMWP reached the 80% bioeffectiveness threshold of the WHO for residual activity in the first five months with 78% residual activity after six months. ImergardTMWP can be used as a blend with chemical insecticides or as a standalone pesticide for mosquito control in Africa.