December 22, 2022 report
Mosquitoes highly resistant to insecticides found in Vietnam and Cambodia
by Bob Yirka , Phys.org

A team of researchers affiliated with multiple institutions in Japan, working with colleagues from Vietnam, Cambodia, Singapore, Taiwan, Indonesia and Ghana, has found evidence of mosquitoes that are highly resistant to common insecticides in both Vietnam and Cambodia.

Insects such as mosquitoes carry a host of infectious diseases, ranging from dengue and yellow fever to the Zika virus and malaria. So scientists have developed a host of chemicals aimed at killing or repelling mosquitoes, most of which are called pyrethroids and target the mosquito's central nervous system. In this new effort, the researchers have found evidence of mosquitoes in Vietnam and Cambodia evolving to become highly resistant to pyrethroids.

The work involved going into the field and collecting mosquitoes in Vietnam, Indonesia, Ghana and Taiwan. The researchers then sprayed each of the samples with permethrin, a pyrethroid that is commonly used in all of the areas where the samples were collected. They found that just the 20% of the mosquitoes collected from Vietnam died. Death rates from mosquitoes in the other samples were as expected.

The researchers then took a look at the genomes of the mosquitoes that had survived exposure to the insecticide and found a mutation in the L982W gene—a gene that has already been linked to resistance in mosquitoes. The team then collected more samples, this time from Singapore and Cambodia, and studied their genes, looking specifically at L982W. They found 10 unique strains with mutations similar to those seen in the Vietnamese mosquitoes—and almost all of them were in Cambodia.

The researchers estimated that up to 78% of the mosquitoes in the samples they collected from Cambodia or Vietnam were resistant to pyrethroid—and those with the pyrethroid mutation were found to have on average a 50- to 100-fold increase in resistance. They also looked for combinations of mutations that lead to resistance and found that those with a combination of L982W and other mutations could survive pyrethroid exposure levels of 500 to 1,000 times more than the amount that normally kills mosquitoes.

The researchers conclude that other countries should begin testing for resistance to determine the true magnitude of the problem.

The work is published in the journal Science Advances.
https://phys.org/news/2022-12-mosquitoe ... etnam.html

Couldn't be from all the sprays that are available at every drink shop

Long read and scientific follow-up for those particularly interested in this topic:

Discovery of super–insecticide-resistant dengue mosquitoes in Asia: Threats of concomitant knockdown resistance mutations
Science Advances
21 Dec 2022
Vol 8, Issue 51
DOI: 10.1126/sciadv.abq7345
Kelly Servick

Genetically engineered mosquitoes resist spreading any form of dengue

Abstract
Aedes aegypti (Linnaeus, 1762) is the main mosquito vector for dengue and other arboviral infectious diseases. Control of this important vector highly relies on the use of insecticides, especially pyrethroids. The high frequency (>78%) of the L982W substitution was detected at the target site of the pyrethroid insecticide, the voltage-gated sodium channel (Vgsc) of A. aegypti collected from Vietnam and Cambodia. Alleles having concomitant mutations L982W + F1534C and V1016G + F1534C were also confirmed in both countries, and their frequency was high (>90%) in Phnom Penh, Cambodia. Strains having these alleles exhibited substantially higher levels of pyrethroid resistance than any other field population ever reported.

The L982W substitution has never been detected in any country of the Indochina Peninsula except Vietnam and Cambodia, but it may be spreading to other areas of Asia, which can cause an unprecedentedly serious threat to the control of dengue fever as well as other Aedes-borne infectious diseases.

Full article: https://www.science.org/doi/10.1126/sciadv.abq7345