Proteins Show Promise For Mosquito Control
(Beyond Pesticides, September 16, 2004) Researchers at the University of Wisconsin-Madison are working on a new, more targeted approach to mosquito management that doesn't require the use of broad-spectrum insecticides. Que Lan, PhD, an insect physiologist, and her colleagues in the entomology department are investigating ways to control mosquitoes by targeting specific proteins in order to inhibit the mosquito's ability to metabolize cholesterol.

Cholesterol, the sticky substance that accumulates on the lining of human arteries, is an important component of cell membranes in both vertebrates and invertebrates. In mosquitoes, it is vital for growth and development as well as egg production. Unlike humans, mosquitoes cannot synthesize cholesterol. They must obtain it from decomposed plants they eat while in their larval stage, living in shallow waters. Plants make phytosterol, which is converted to cholesterol in the mosquito's gut.

Since cholesterol is hydrophobic, organisms must have a way to shield it from water when transporting it in a liquid medium, such as blood or cell fluids. That shield is typically a carrier protein. Using the yellow fever mosquito, Dr. Lan and her research colleagues discovered that a sterol-carrying protein, AeSCP-2, is the vehicle that transports the cholesterol in mosquito cells.

Lan and her colleagues reasoned that if they could block the carrier protein, it would disrupt the uptake of cholesterol by the mosquito. Screening what she calls "a small chemical library of 16,000 compounds," Lan and her team found 57 compounds that inhibited the cholesterol-binding capacity of SCP-2. The top five most viable inhibitor compounds were then tested on mosquito larvae, producing promising results--the larvae died. The results were dose-dependent; that is, at higher concentrations, larger numbers of larvae died. Still, the concentrations were very small, Lan says, in the range of 10 parts per million.

"Control is urgent," Dr. Lan, who is from China, says. "Mosquito-borne illnesses are endemic in parts of China. Malaria is a big problem in south-central China. South of the Yangtze River the infant mortality rate is high, especially in homes without screens on the windows."

The common insecticides that are used to kill mosquitoes are broad-spectrum adulticides, which kill all adult flying insects they contact, including mosquito predators such as dragonflies, leaving populations with fewer natural controls. While traditional adulticide methods look like action, in actuality they accomplish very little. Dr. Lan believes that a more fine-tuned chemical approach is more practical: only one compound is selected, it works for a short period, and it targets a single insect. "People might ask, 'Why do we need more pesticides?'" Lan says. The answer is twofold: resistance and the effect on non-target species. "I believe you should develop smart pesticides to only kill the mosquitoes," Lan says. "We don't want to go down the same road as DDT."

To that end, her team is testing the most promising handful of SCP inhibitor compounds on a variety of insect and vertebrate species. So far three of the five compounds tested were not toxic to mouse cells and the other two were only slightly toxic. They will also test the compounds on other pest species, including flies, roaches and termites. Environmental and degradation tests have yet to be performed. "We want a specific target with low residue time- two to three weeks and it should be degraded," Lan says.

While more research is needed to find out whether this particular technique will be a viable as well as safe alternative to adulticides, there are other least-toxic methods of mosquito control already. In the last few months, there have been quite a few promising studies on alternative methods of insect control, such as cinnamon oil to control mosquitoes, garlic oil to repel birds, and a non-toxic lotion to control head lice.

Read more about Dr. Lan's research in Medical News Today

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