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Microbial Repellent In the fight against mosquitoes, bacteria may come to the rescue
Photo by Jeff Miller
A study from the Department of Entomology shows that a bacterial extract may serve as an effective mosquito repellent in smaller doses than common deterrents DEET and picaridin. Here, a mosquito feeds on the hand of entomology professor Susan Paskewitz during the collection of live specimens for unrelated field research.
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SUMMER 2019
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hen Que Lan passed away unexpectedly of complications from gastric cancer in 2014, the UW entomology professor left behind a promising research project. Her work suggested bacteria might offer a new and effective way to repel mosquitoes. She had started out looking for bacterial compounds that could kill mosquitoes. Before her passing, Lan discovered that, although one particular bacterial extract was not lethal to mosquitoes, when it was put in their food, the insects refused to eat. Lan’s colleague, entomology professor Susan Paskewitz, helped secure additional funding to keep the study going and found a scientist, Mayur Kajla, interested in carrying the work forward. In January 2019, their findings were published in the journal Science Advances. Paskewitz and Kajla, an assistant scientist in the Department of Entomology at the
time of publication, describe the first mosquitorepelling compounds to be derived from microbes. “We didn’t come at it thinking we would find a repellent,” says Paskewitz, chair of the entomology department and director of the Midwest Center of Excellence for Vector-Borne Disease. “It was a bit of serendipity.” 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 the compounds to be effective against Aedes aegypti, Anopheles gambiae, and Culex pipiens — mosquito species known to transmit diseases such as Zika, West Nile, malaria, and chikungunya, which afflict millions of people worldwide. Whether these natural chemical compounds, called fabclavines, are suitable for human use remains to be determined. But the study opens up a new area of exploration in the search for insect-repelling and insect-killing compounds, Paskewitz says. When Kajla joined the project, he designed a set of experiments to test the repellent potential of the bacterial extract and identify the compounds responsible. He modified a commercial mosquito feeding system to more closely mimic a mosquito feeding on a human. For instance, he selected a skin-like membrane to contain a special, red-dyed mosquito diet that simulates human or animal GROW ONLINE blood. He also tested a variEXTRA: VIDEO ety of cloth coverings to sit See how the bacterial atop the membrane, which extract affects feeding mosquitoes at would be coated with the grow.cals.wisc.edu/ repellents being screened. microbial-repellent. 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 fed (engorged with red liquid) or unfed. The mosquitoes did not feed when the cloth was coated in repellent. He then tested purified extracts from the bacteria and, with assistance from UW–Madison co-author
