NMSU researchers identify top commercial products to repel mosquitoes

May 23, 2016

As Congress haggles over how many millions or billions of dollars to spend to help stop the spread of the Zika virus in the U.S. before summer, researchers at New Mexico State University are already testing wearable mosquito repellent devices to determine which ones can best help us protect ourselves against these insects.

“The goal is to find out what works and what doesn’t,” said Immo Hansen, an NMSU associate professor of biology involved in the investigation. “There are so many products on the market that simply don’t work, so I think it’s really important to test them in a scientific way.”

This month, a group from Hansen’s Molecular Vector Physiology Lab, in the College of Arts and Sciences, began a series of tests to determine the effectiveness of a dozen commercially available wearable repellents, including clip-ons and wristbands. Though the study is ongoing, preliminary data revealed that citronella-based bracelets and wristbands have little effect on mosquitoes, whereas OFF Clip-On devices not only repel mosquitoes, they also kill them.

“Some people are really resistant to putting repellents on their skin, so they would rather choose a wearable device,” said Stacy Rodriguez, manager of NMSU’s Molecular Vector Physiology Lab and lead researcher on this project. “Right now, we are just trying to see if the wearable devices are as effective as the spray-on devices.”

The group plans to publish the results of this research by mid-summer.

This analysis is a follow-up to a study the group conducted last fall on 10 commercially available spray-on repellents. During this experiment, Rodriguez and her colleagues recognized the most reliable sprays as DEET products and lemon eucalyptus-based insect repellents.

For the current study, the group is testing the wearable devices using a 70-foot wind tunnel located in an NMSU research facility. After taking baseline readings, the researchers put on the repellent devices and position themselves upwind of a series of test cages. Depending on the product’s repellency, the caged mosquitoes either fly away from the test subjects or toward them.

The wearable devices are being tested against the same two species of mosquito used in the spray repellent study: the Asian tiger mosquito (Aedes albopictus) and the yellow fever mosquito (Aedes aegypti), both of which carry the Zika virus.

“These two mosquitoes have very different levels of attraction to even one certain individual,” Rodriguez said. “Since attraction varies, repellency is also going to vary, so it’s important to test multiple species when you’re looking at repellents and their efficacy.”

Thanks to body chemistry, mosquitoes are also more inclined to bite someone who “smells” good to them.

“Everybody has a different bacterial flora on his or her skin,” Hansen said. “The bacteria break down components of sweat and produce a different set of olfactory clues for the mosquitoes. Some people just smell better to mosquitoes than others, and there’s really nothing you can do about that except wear repellents. There’s nothing you can do to change the bacterial flora on your skin.”

Consequently, these chemical differences can impact which repellents work best for you.

“Something that might work for one person because of his or her body chemistry, might not work for somebody else because he or she has different chemistry,” Rodriguez said.

While the Asian tiger mosquito hasn’t established significant populations in New Mexico, Aedes aegypti – one of the primary vectors of dengue, Zika virus and yellow fever – can be found in your backyard in Las Cruces.

“Be aware; prepare,” Hansen said. “Get yourself a good repellent, wear long sleeves, long pants. Try to avoid getting bit.”

The mosquito that carries the Zika virus can breed in as little as one centimeter of standing water, Hansen explained. For those with ponds, his recommendation was to get Gambusia, or mosquito fish, from the Doña Ana County Vector Control to keep backyard mosquito populations at bay.

Next fall, Hansen and Rodriguez plan to investigate mosquito attractants for use in baits. Surprisingly, even though humans attract mosquitoes all the time, Rodriguez explained that creating a chemical to attract mosquitoes is actually harder than repelling them.

“We have such complex odors that it’s actually hard to emulate that in cream or a bait trap,” she said. “It’s actually much more complex than creating something that disguises your human smell.”

For more information on NMSU’s Molecular Vector Physiology Lab, visit http://biology-web.nmsu.edu/~hansen/index.htm.

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