Media Reports on UW-Madison Researchers Using Bacteria in Worms as Mosquito Repellent

Bacteria In Worms Make A Mosquito Repellent That Might Beat DEET

January 16, 2019

Jonathan Lambert, NPR

The next great insect repellent might come from a strain of bacteria that lives inside a common parasitic worm.

A study published Wednesday in Science Advances has found that a compound derived from these bacteria is three times more potent than DEET in repelling mosquitoes. More research must be done to demonstrate its safety, but this bacterial chemical could play an important role in the fight against mosquito-borne illness.

Susan Paskewitz, a professor of entomology at the University of Wisconsin-Madison who oversaw the study, explains that the project started in the lab of her late colleague, Que Lan. She and her student Il-Hwan Kim were studying bacteria called Xenorhabdus budapestensis, which lives inside the tiny roundworms called nematodes. These nematodes parasitize insects in the soil, sneaking into their bodies and releasing hordes of Xenorhabdus, which soon kill the insect. Then, without the insect's immune system to contend with, the nematodes devour the carcass and multiply.

According to Paskewitz, Lan wanted to crack Xenorhabdus' insecticidal code in hopes that it might lead to a novel mosquito killer. She put the bacteria into the artificial blood supply she feeds to her mosquito colonies, hoping they would ingest the bacteria and she could track whether the mosquitoes were harmed. But her mosquitoes wouldn't go anywhere near the treated blood, much less ingest it. "The mosquitoes would die from drying out rather than touch the thing," says Paskewitz. That observation stuck in Paskewitz's mind, suggesting that something produced by these bacteria make might be useful as an insect repellent.

Read more here.

A new kind of mosquito repellent that comes from bacteria

January 17, 2019

Kelly April Tyrrell, UW-Madison

People may soon have a new weapon in the battle against mosquitoes, and it comes from an unusual source: bacteria.

Published Jan. 16 in the journal Science Advances, University of Wisconsin–Madison researchers describe the first mosquito-repelling compounds to be derived from the microbes.

These compounds, purified from extracts from the bacterium Xenorhabdus budapestensis, appear to work at lower doses than repellents currently on the market, including DEET and picaridin. The study showed them to be effective against Aedes aegyptiAnopheles gambiae and Culex pipiens, mosquito species known to transmit diseases such as Zika, West Nile, malaria and chikungunya, diseases that afflict millions of people worldwide,.

Whether these natural chemical compounds, called fabclavines, are suitable for human use remains to be determined, but the study, says UW–Madison Professor of Entomology Susan Paskewitz, opens up a new area of exploration in the search for insect-repelling and insect-killing compounds.

“We didn’t come at it thinking we would find a repellent,” she says. “It was a bit of serendipity.”

In fact, the project did not begin with Paskewitz at all. It started with her colleague, Que Lan, who tragically passed away in 2014 from complications of cancer. At the time, Lan was looking for bacterial compounds that would kill mosquitoes. Paskewitz helped secure additional funding to keep the study going and found a scientist, lead study author Mayur Kajla, interested in carrying the work forward.

When Kajla joined the project, the research team already knew that extracts from the bacteria did not kill mosquitoes but when it was added to their food, the mosquitoes refused to eat. He designed a set of experiments to test the repellent potential of the bacterial extract and identify the compounds responsible.

Using a commercial mosquito feeding system, Kajla made modifications to more closely mimic a mosquito feeding on a human being. For instance, he selected a skin-like membrane to contain a special, red-dyed mosquito diet that simulates human or animal blood. He also tested a variety of cloth coverings to sit atop the membrane, which would be coated with the repellents being screened.

Kajla coated the cloth with water, DEET or picaridin and allowed mosquitoes to feed for 30 minutes before freezing them and counting the number that were engorged with red liquid (fed) or unfed. The mosquitoes did not feed when the cloth was coated in repellent.

Read more here.