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Scientists Spice Up Their Mosquito Weaponry with Mustard
Scientists with the Agricultural Research Service (ARS) have shown that seed meal from plants in the mustard family can kill mosquito larvae, which start their lives in stagnant water before emerging into winged adults that take to the air in search of a blood meal.
Mustard. Photo: Mak/Unsplash
At the ARS National Center for Agricultural Utilization Research in Peoria, Illinois, a team of scientists has set their sights on the discovery and development of environmentally friendly approaches for controlling mosquitoes at the habitat level and for individual consumer applications.
On a habitat basis, they’re focusing on products derived from plants and other natural sources that may offer an ecologically friendly way to target mosquito larvae, the pest’s most vulnerable life stage.
Together with ARS co-authors Robert Behle, Mark Berhow, Susan McCormick, Steven Vaughn, Ephantus Muturi and William Hay, Lina Flor-Weiler, an entomologist with the ARS center’s Crop Bio-protection Research Unit is the first to report the potential of mustard seed meal to kill mosquito larvae, which feed on bits of organic matter and microorganisms in shallow bodies of water.
As larvae, the pests are largely confined to a concentrated area after hatching from eggs deposited there by adult female mosquitoes—a scenario that makes for an ideal pre-emptive strike against the pests before they can mature.
Sometimes, the environmental sensitivity of these areas or the presence of non-target organisms warrant a non-chemical solution to control mosquito larvae, such as with formulations that inhibit their growth, suffocate them or infect them with specialized bacteria.
In studies begun in 2022, the researchers examined the larval-killing potential of isothiocyanates, a group of plant defense chemicals that are released when mustard seed meals are soaked in water.
“The mustard plant stores inactive defense compounds (glucosinolates) in the seed that can be converted into biologically active isothiocyanates by enzymes called myrosinases,” explained Hay, an ARS plant physiologist.
Prior research by other groups has shown that isothiocyanates can kill insect pests and soilborne parasites and pathogens, including root-damaging nematodes and disease-causing fungi.
The researchers prepared seed meal from four types of mustard family plants (brown mustard, pennycress, garden cress and white mustard) and added varying concentrations of them to small beakers of water containing larvae of Aedes aegypti mosquitoes.
Of the four seed meal types, garden cress proved the most lethal, killing more than 95 percent of mosquito larvae after only 24 hours and 100 percent in less than 48 hours.
All seed meals were toxic to the larvae, except for a pennycress treatment that had been heated. This was intentionally done to deactivate myrosinase enzymes (which are necessary for the production of isothiocyanate) and confirm that their absence in the seed meal allowed the larvae to survive.
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