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More than 1 million people a year die from mosquito-borne illnesses such as malaria, dengue virus, and West Nile virus. And earlier this year, a dramatic increase in birth defects in Brazil was linked to the Zika virus, another mosquito-transmitted disease. Suppressing and controlling the spread of mosquito populations remains a major health challenge for nations in tropical and subtropical regions. Researchers and companies are working worldwide to develop new agents that are safe, effective, and affordable to protect people from mosquitoes. Here, we highlight three patents reporting new mosquito-control strategies from the databases of Chemical Abstracts Service (CAS).
Mosquitoes rely on plant sugars for energy. While female mosquitoes also drink blood, plant sugars are the only food source for male mosquitoes. Noting this, Michelle A. Brown, Martin A. Lomeli Jr., and Samer Elkashef of Olfactor Laboratories, a California-based biotech firm, developed a sugar mixture that kills mosquitoes (WO 2015200753) by exploring the mosquito-killing power of several mixtures of toxic and nontoxic sugars. They found that a 1:1 mixture of sucrose with glycyrrhizin was the most effective, with the sucrose attracting hungry insects and glycyrrhizin killing them through an unknown mechanism. After mosquitoes were fed the mixture for three days, about 50% of the insects died compared with only 2% of mosquitoes fed a sucrose-only diet. Not surprisingly, more male mosquitoes died than did female ones after being exposed to the toxic mixture. The scientists claim in the filing that because the mixture is derived from natural products, it should be less harmful to the environment and human health than synthetic insecticides.
Pyrethroids are a class of insecticides that cause paralysis by preventing sodium ion channels from closing in insect nerve cells. Unfortunately, pyrethroid resistance is becoming a major hurdle in effectively suppressing mosquito populations. The usual approach to addressing such resistance—rotating through conventional insecticides—has created mosquitoes resistant to multiple classes of compounds. A serendipitous discovery from Valent BioSciences suggests a new approach to attacking resistant mosquitoes (US 20150094367). The Valent team found a mixture of permethrin, a commonly used pyrethroid, and fatty acids, such as octanoic, nonanoic, and decanoic acids, knocked down drug-resistant mosquitoes better than it did their nonresistant brethren. The amount of time to kill 50% of the resistant mosquitoes was 3.2 minutes, compared with 5.3 minutes for the nonresistant insects. The fatty acids alone were equally nonlethal to both mosquito groups, and exposure to just permethrin had the expected result of killing nonresistant mosquitoes quicker. Valent did not respond to C&EN’s request to elaborate on the possible mechanism behind this phenomenon before press time. But in its filing, the firm says that this fatty acid formulation may allow for the reuse of other pesticides that are no longer effective on resistant mosquitoes.
Insecticide resistance in mosquitoes is a complex phenomenon that arises from constant exposure to the same class of compounds over multiple insect generations. Scientists at Bayer CropScience recently patented the simultaneous use of two different classes of insecticides, pyrethroids and neonicotinoids, to combat resistant mosquitoes (WO 2015197482). These two compound classes act on different proteins on the surfaces of insect cells, but they both cause paralysis and eventual death in insects. The Bayer team sprayed deltamethrin and clothianidin—a pyrethroid and a neonicotinoid, respectively—on different types of surfaces to test how well the mixture killed resistant mosquitoes. Five weeks after the treatment of a concrete surface, up to 97% of the mosquitoes that came into contact with the surface died within 24 hours. The mortality rate 60 weeks after treatment was still an impressive 83% for insects bumping into the surface in the past 24 hours. Justin McBeath, a vector control specialist at Bayer, tells C&EN that the firm has started a trial program in several endemic countries to test the real-world efficacy of the mixture.
Mitch Garcia wrote this month’s Patent Picks in collaboration with CAS. This feature reports on trends CAS scientists observe from patents in CAS databases. Please send comments and suggestions to patentpicks@acs.org.
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