“Mosquitoes are by far the world’s most medically significant insects.”
So says David Moffett, a professor in the School of Biological Sciences, who, with his wife Stacia Moffett, an associate professor, has been studying structure and functions of the mosquito stomach tract for the past four years. The species, Aedes aegypti, a yellow fever carrier, is under particular scrutiny, and David leads the research.
World-recognized problem
The abstract from Moffett’s research project proposal states, “They (mosquitoes) are potential vectors for approximately 100 arboviruses that cause human disease, including yellow fever, dengue and a number of forms of encephalitis. They also transmit nematodes that cause elephantiasis, and plasmodia that cause malaria.”
What that mouthful means is that mosquitoes are, as Moffett says, one of the world’s most dangerous animals.
The eggs can survive brutal winters and yet also be found in deserts, if a puddle of water can last long enough for them to hatch and form larva and for the adults to take flight.
And the world — America in particular — is looking aggressively for control solutions.
Basic science at work
Moffett says that in this kind of research, it is hard to separate knowledge gathering from the probable application of finding safer ways to destroy mosquitoes. But he insists that, for the moment, he is only researching the “gut” function of the mosquito, wherever that information may lead.
“We are gaining a little piece of knowledge that can grow to applications not yet foreseen,” he says.
He also admits that without such an application in view, it would have been difficult to get the National Science Foundation grant, about $200,000, to fund the research.
Why the gut, specifically? Again, it’s science for its own sake.
Researchers have found that the anterior part of the mosquito gut tract is alkaline rather than acidic like most animals. And the concentration is high, about pH10, which is strong enough to kill ingested microorganisms and viruses. But secretions become more acidic towards the posterior part of the tract. This observation, plus the physiological nature of the digestive system, leads Moffett to believe that the larva relies on a sophisticated and highly controlled function of alkali recycling to maintain tract chemistry and trigger digestion.
Moffett’s research has discovered many biochemical and structural details to support such a view.
The investigation is, necessarily, microscopic, and Moffett credits Stacia, whom he calls “a skilled microsurgeon,” for getting the tissue samples.
The samples can survive for a couple hours, he says, but alkali production ceases fairly soon, so they have to work fast to study the process, which includes Stacia making neurochemical images.
He also collaborates with researchers from Georgia, Notre Dame and the University of California Irvine.
Getting them young
Potential application always remains in view. Anything that could disrupt the cycle or be immune to the alkali could be developed into a control.
Here is one possibility.
Larvae are stationary within their water environment, sucking in “detritus” (disintegrating debris) for food, as well as microorganisms. If health officials could introduce microbes or virus agents that the larva would normally ingest, but which are chemically altered to withstand the alkali in the gut, those agents could colonize within the larva, destroying it from the inside. The mosquitoes never get the chance to mature and take wing to ports unknown.
Another possibility is to use information about the neural communication pathways and the signal chemicals that control the system to devise a way of disrupting alkali production, thus allowing the “endemic” (naturally occurring) organisms in the water to kill the larva.
Moffett believes that the gut tract in the mosquito could be so specialized that such approaches would work.
Specific controls like these are considered “third generation.”
The next generation
Moffett anticipates his research will be used in developing third-generation insecticides — chemicals which target a particular species in narrow ways.
The first-generation insecticide was DDT, an indiscriminate killer of all insects. DDT is also inert; it is not biodegradable. Public concern over potential effects to all animal life put an end to its use.
Second-generation insecticides, like “BT,” are alkali-resistant and work specifically against arthropods, which includes mosquitoes. And these compounds eventually break down in the environment.
But a well-publicized incident in the empire state demonstrates how second-generation solutions still haven’t solved the problem.
A couple years before Sept. 11, and the crash of an airliner in a New York City neighborhood a few weeks later, New Yorkers suffered another menace from the air.
People were contracting West Nile Fever — something Moffett calls “an exotic illness” — from mosquito bites.
“The sudden appearance of West Nile Fever in the U.S. reminds us that in an era of global travel, geography does not protect us against the spread of infectious disease,” Moffett commented.
Health officials fought a successful battle with a second-generation insecticide. Unfortunately, the aerially dispensed weapon ultimately washed into the Atlantic, where another arthropod population, lobsters, was also affected before substance breakdown was complete.
The goal for third-generation insecticides is species specificity, which Moffett says is a challenging task. For example, mosquitoes have proteins found in other animals and in humans, making proteins difficult to target for control and still maintain specificity.
The chemicals, or the microorganisms they alter, must be harmless to the environment and other life forms. Only the targeted vector must be affected.
Thus, the more expert he and other researchers become in the gut tract of the mosquito, the greater the chance for success by those who later pursue application. And targeting the larva’s gut means controls can be dispensed more locally than widespread aerial spraying.
Other duties
Moffett earned his bachelor of science degree in zoology from Duke University and his Ph.D. in biology from Miami Coral Gables. He came to WSU in 1974 as a postdoctoral fellow, attaining a position as associate professor soon afterward.
Besides his research, he is also a student adviser and the coordinator of the premedical and predental programs. He teaches cell and system physiology to third-year students in pharmacy and other health fields.
He says he’s always been interested in insects, though more in caterpillars at the start. He sort of drifted into mosquito research, his skills and knowledge complementing Stacia’s. And considering how promising his findings appear, it would seem good that they decided to collaborate.
So when you’re sitting out on your porch on a warm summer evening, and you hear that high-pitched whine around your ear that can mean only one thing, be glad that David and Stacia Moffett are discovering information that could one day put an end to the pest.
