Mosquito bites are much more than just a red and itchy summertime nuisance. The diseases that they carry are notoriously difficult to control and kill over 700,000 people worldwide every year. What’s more, many mosquitoes have developed resistance to the synthetic insecticides–the same substances that can also pose environmental and health risks.
As a solution, microbiologists are looking into biopesticides derived from living organisms. According to a study published July 7 in the journal Applied and Environmental Microbiology, a bacteria isolate collected from the Mediterranean island of Crete works as insecticides against Culex pipiens molestus mosquitoes. Nicknamed the London Underground mosquito because they bit people sheltering in the city’s underground train stations during World War II, this species can transmit dangerous human pathogens, including West Nile Virus and Rift Valley Fever Virus.
Extracts with these metabolites produced by three isolates killed 100 percent of mosquito larvae within 24 hours of exposure. It’s those metabolites that could be used to develop biopesticides that have minimal ecological side effects, according to the team.
“They degrade more quickly in the environment and therefore don’t accumulate, and they often don’t kill such a wide range of different insect species as chemical insecticides,” said George Dimopoulos, a study co-author and molecular entomologist and microbiologist at Johns Hopkins University in Baltimore and at the Institute of Molecular Biology and Biotechnology (IMBB) in Crete.
[ Related: Mosquitoes can sense our body heat. ]
Digging for bacteria
In microbiology, an isolate is a single species of bacteria that has been separated out from a mixed culture and also obtained from a pure culture. As a result, all of the bacteria in the culture are the same type. This makes it easier for biologists to study and identify that specific bacteria or bacterium.
For this new study, Dimopoulos and IMBB molecular biologist John Vontas collected 186 different samples from 65 locations across the island of Crete. The samples included topsoil, soil from around plant roots, plant tissues, water samples, and dead insects. Then, they exposed C. pipiens molestus larvae to water solutions that had the most promising isolates found in the samples. Killing mosquito larvae before they grow into adult mosquitoes is a common control method since the insects reproduce so quickly.
More than 100 of the isolates killed all of the mosquito larvae within a week and 37 of those killed the larvae within three days. Those 37 isolates represented 20 genera of bacteria, many of which have not previously been identified for use in biopesticides, according to Dimopoulos.
Additional analysis revealed that the rapid-acting bacteria did not kill the larvae through infection. Instead it spurred the larvae to produce compounds like proteins and metabolites–small molecules produced when an organism is breaking down food. This method is promising because it suggests that an insecticide using this bacteria would not depend on the microbes staying alive. Not being too dependent on living microbes could potentially make the biopesticides work longer. This method could have implications for controlling mosquitoes and potentially agricultural pests.
From discovery phase to science phase
The team is also studying the chemical nature of the insecticidal molecules more closely and pinpointing whether they are proteins or metabolites. They’re also mapping out how much pesticidal activity the bacteria is capable of, including screening the isolates against other strains of pathogen-bearing mosquitoes and insects that threaten crops.
Since biopesticides often degrade quickly and require multiple applications, finding the right way to formulate and deliver these compounds will be a challenge in the future.
“It’s now entering the basic science phase to understand the molecules’ chemical structures and modes of action, and then we’ll shift to a more applied path, really aiming at prototype product development,” Dimopoulos said. “There is a major push toward developing ecologically friendly insecticides.”
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