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Mosquito

Mosquitoes, thriving in Wisconsin after recent rains, could someday be combated with repellent made from bacteria instead of chemicals, according to UW-Madison researchers.

Two compounds from a bacterium found on worms prevented mosquitoes from feeding in a campus lab experiment. The amount of bacteria needed to ward off mosquitoes was three times less than for DEET and eight times less than for picaridin, two chemicals found in many insect repellents.

The study showed the bacterial compounds to be effective against several mosquito species, including those known to transmit diseases such as Zika, West Nile, malaria and chikungunya.

“Maybe we can use this as some kind of repellent to replace or supplement some of the things out there that people are sometimes a little more nervous about using,” said Susan Paskewitz, chairwoman of UW-Madison’s Department of Entomology and one of the researchers involved.

Susan Paskewitz

Paskewitz

Some consumers worry about the health effects of DEET and picaridin, even though there’s no scientific evidence to support such concerns, Paskewitz said.

The new research involves purified extracts from the bacterium Xenorhabdus budapestensis, which often uses nematode worms as a host, Paskewitz said. When nematodes invade insects, they release the bacterium to kill them, she said.

Que Lan, a UW-Madison entomology professor who died from cancer in 2014, started the project. She was studying whether the bacterium could be put in water or a mosquito food source to kill mosquitoes and control their populations.

When Lan tried to get adult mosquitoes to feed on a food source laced with the bacterium, “they wouldn’t touch it,” Paskewitz said. “That was fascinating because the adult female was somehow recognizing that it was not a good place for her to go.”

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Mayur Kajla

Kajla

The finding led to a study of compounds from the bacterium, called fabclavines, as potential repellents. Scientist Mayur Kajla used a cloth, a skin-like membrane and a red-dyed mosquito diet simulating blood to test how well the compounds, DEET and picaridin deterred mosquitoes from feeding.

The dose of fabclavines required to prevent feeding was considerably less than for the chemicals, Kajla said. The finding was published in January in the journal Science Advances.

mosquitoes with red

Mosquitoes given a regular food source without bacterial compounds have red guts.

mosquitoes without red

The lack of red in these mosquitoes' guts shows they fed on a food source with bacterial compounds.

Paskewitz and Kajla are working with UW School of Medicine and Public Health researchers to test the compounds in human cells. Initial tests suggest some toxicity, which could be problematic, but the investigation continues.

The low dose of the compounds required to ward off mosquitoes could mean less toxicity, Paskewitz said. It’s too early to know how costly it would be to make repellent with the bacterial compounds instead of chemicals, she said.

Animal studies would be next, possibly followed by human trials. Paskewitz and Kajla have filed for a patent on the work through the Wisconsin Alumni Research Foundation.

“I am itching to put it on my hand and put it in a case of mosquitoes, but I can’t do it yet,” Paskewitz said in a statement.

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