A bacterial compound might make for a better natural mosquito repellent. (Credit: MNStudio/Shutterstock) In the search for new compounds to fight off mosquitos, researchers have struck pay dirt in an increasingly common location: Soil bacteria. A pair of molecules produced by a species of insect-infecting bacteria appear to convince mosquitos not to feed on human blood, researchers from the University of Wisconsin-Madison report Wednesday in Science Advances. The find could eventually serve an alternative to chemical insect deterrents like DEET. The researchers were looking at a genus of bacteria known as Xenorhabdus, which lives symbiotically with a species of dirt-dwelling nematode that parasitizes insects. Xenorhabdus live inside the nematodes, and though scientists don't quite know how, the microscopic worms can't successfully infect and utilize their insect hosts without the bacteria. To help it with this task, Xenorhabdus produces an array of compounds known as secondary metabolites — compounds that aren't directly necessary for survival, but which grant the bacteria extra abilities. Scientists have recently been looking at secondary metabolites in a range of microbial species to search for things that might have useful properties. The Wisconsin researchers turned their attention to Xenorhabdus, and because they knew it was specialized to infect insects, they thought it might be a good place to look for potential mosquito deterrents. That hunch turned out to be accurate. Extracts from the bacteria kept three species of mosquito from coming near food or from actually feeding on it in the lab. Further analysis revealed two molecules known as fabclavines to be the likely repelling agents. In tests, the two fabclavines were as good or better than DEET and picaridin — two commonly-used artificial mosquito repellents — at keeping mosquitoes from both landing and feeding. This included Aedes aegypti mosquitos, which can spread Zika, dengue, chikungunya and other infectious diseases. Mosquitos spread diseases when they pierce our skin to sip blood, so preventing them from feeding — instead of killing them outright — would be enough to protect humans. There haven't been any tests of the fabclavines on humans yet to see if they're safe for use, and the researchers say that further work lies ahead to pin down whether both compounds or just one of them are necessary to deter mosquitos. It's also unknown whether these compounds would be cheaper and easier to produce than DEET, another consideration for getting them to market. But, they could serve as effective organic alternatives to DEET, which is largely considered safe, though it's not recommended for infants and there's evidence that it can harm some species of fish. Yet again, it's proof that when it comes to human problems, nature might already have a solution.