Adding small amounts of liquid soap to certain pesticides can significantly increase their effectiveness against malaria-carrying mosquitoes, scientists found.
Research shows that combining liquid soap and neonicotinoid insecticides can boost their effectiveness more than tenfold.
The findings offer hope in efforts to tackle disease-carrying mosquitoes that have becoming increasingly resistant to insecticides.
The study, published in PLOS Neglected Tropical Diseases, was led by Dr Colince Kamdem and Dr Caroline Fouet of the University of Texas at El Paso.
“Mosquitoes have become strongly resistant to most insecticides over the past two decades,” said Dr Kamdem, the study's lead author.
“It's a race now to develop alternative compounds with new modes of action.”
Dr Fouet added that neonicotinoids are a promising alternative, "but their potency against certain mosquito species needs boosting".
“In this case, soap is the boosting substance," she said.
In 2020, there were an estimated 241 million malaria cases and 627,000 deaths, the World Health Organisation reported.
The disease, prevalent in sub-Saharan Africa, Asia and Latin America, causes symptoms including fever, fatigue, headaches and chills.
Dr Kamdem, who previously worked at Cameroon’s Centre for Research in Infectious Diseases, stumbled on the effectiveness of soap while conducting routine insecticide tests.
He observed more mosquito deaths when a seed oil-based product, a compound similar to kitchen soap, was added to insecticides.
This observation led to the testing of three low-cost, linseed-oil based soaps – Maitre Savon de Marseille, Carolin Savon Noir and La Perdrix Savon – with four different neonicotinoids.
“All three brands of soap increase mortality from 30 per cent to 100 per cent, compared to when the insecticides were used on their own,” said Ashu Fred, the study's first author and a PhD student at the University of Yaounde 1 in Cameroon.
The team reported no benefits when soap was added to pyrethroid insecticides. Despite this, the study opens new avenues in the fight against malaria.
“We would love to make a soap-insecticide formulation that can be used indoors in Africa and be healthy for users," Dr Kamdem said. “There are unknowns as to whether such a formulation will stick to materials like mosquito nets, but the challenge is both promising and very exciting.”