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A mixture of anti-mosquito compounds isolated from a Gram-negative bacterium called Xenorhabdus budapestensis has a powerful deterrent activity against three important mosquito species (Aedes aegypti, Anopheles gambiae, and Culex pipiensand works at lower doses than currently available repellents, including DEET and picaridine, according to a study published in the newspaper Progress of science.
Aedes aegypti mosquitoes after an experiment; the lack of red in their bowels indicates that the compounds repelled the mosquitoes, who chose not to feed themselves. Image credit: Mayur Kajla.
"It remains to be determined whether these natural chemical compounds, called fabclavines, are suitable for human use, but the study opens a new field of exploration for the search for repellent and destructive compounds. insects, "said Professor Susan, lead author of the study. Paskewitz, researcher at the Department of Entomology at the University of Wisconsin-Madison.
"We did not think we were going to find a repellent. It was a bit of luck.
Before the study, Professor Paskewitz and his colleagues already knew that extracts from Xenorhabdus budapestensis, a bacterial symbiont of Steinernema bicornutum nematodes, did not kill the mosquitoes, but when the extracts were added to their food, the mosquitoes refused to eat.
They designed a set of experiments to test the repulsive potential of the bacterial extract and identify the responsible compounds.
Using a feed system for commercial mosquitoes, they made modifications to mimic more faithfully a mosquito feeding on a human being. For example, they chose a skin-like membrane to contain a special red-dyed mosquito diet that simulates human or animal blood. They also tested a variety of fabric liners to sit on the membrane, which would be covered with the repellents to be filtered.
The researchers coated the tissue with water, DEET or picaridin and let the mosquitoes feed for 30 minutes before freezing and counting the number of those who were engorged with red fluid (fed) or not fed. Mosquitoes did not feed when the cloth was coated with an insect repellent.
They then tested purified extracts of the bacteria and discovered that an extract dominated by two molecules of fabclavine effectively deterred mosquitoes from feeding themselves.
When comparing efficacy against picaridine and DEET found in more than 500 insect repellents registered with the US Environmental Protection Agency, bacterial extract was effective at doses eight times and three times lower respectively.
"If you can use less of an active ingredient in a formulation, it may cost less," said Professor Paskewitz.
"The compounds extracted from Xenorhabdus budapestensis may still be useful for other applications and continue to explore their potential, "said Dr. Mayur Kajla, lead author of the study, also from the Department of Entomology at the University of Wisconsin-Madison.
"These compounds may prove more effective against more arthropods," added Professor Paskewitz.
"DEET works against ticks, but it's not as effective as mosquitoes. We will test bacterial compounds against other types of stinging insects and their related species. "
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Mayur K. Kajla et al. 2019. Bacteria: a new source of energy to deter mosquitoes. Progress of science 5 (1); doi: 10.1126 / sciadv.aau6141
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