DAVIS, Calif. — Six scientists, led by British researcher Gregor Devine, and including epidemiologist and dengue mosquito researcher Amy Morrison of the University of California, have found a way to get mosquitoes themselves to transport an insecticide to the places where they lay their eggs.
The day-biting mosquito Aedes aegypti takes a blood meal and then rests in a dark place before heading for water to deposit her eggs. Her eggs normally develop into larvae, pupae and adults; adults are capable of transmitting the killer disease, dengue.
The scientists determined they could place a cloth impregnated with a powdered larval insecticide inside the insect's resting place. The powder will stick to her body when she buzzes off to an aquatic habitat to lay her eggs. There the larvicide will kill not only her offspring but other immature mosquitoes at this site.
When humans treat aquatic habitats with insecticides, the process can be difficult, time-consuming and expensive. When mosquitoes apply insecticides, this targets the exact breeding site (from a discarded tin can to flower vase saucer to sewage seeps) and amplifies the effect because every adult mosquito completes several resting and egg-laying cycles during its lifetime, Devine said.
The research, "Using Adult Mosquitoes to Transfer Insecticides to Aedes aegypti Larval Habitats," was published June 29 in the Proceedings of the National Academy of Sciences.
Devine, with Rothamsted Research in Hertfordshire, United Kingdom, and Morrison, with the UC Mosquito Research Laboratory, have been working together on a variety of field experiments on mosquitoes, including the use of adult mosquitoes to kill their young via a larvicide.
"A major barrier to mosquito control for dengue has been treating all of the infested containers," said Thomas Scott, director of UC Mosquito Research Laboratory. "This is a creative way to exploit the ecology of the system by using the mosquitoes themselves to treat all containers, including the ones that are most difficult for humans to find. This is an exciting new development with important public health implications."
The field work took place in the Amazon city of Iquitos, Peru, where Morrison has studied dengue since 1999. Iquitos, where dengue is endemic, is the most populous city in the world that cannot be reached by road.
The insecticide used in the research — pyriproxyfen — kills larvae, but does not harm people or adult mosquitoes. The World Health Organization declared it safe for drinking at 300 parts per billion, which is 1,000 times the dose needed to control Aedes aegypti.
Some 2.5 to 3 billion people, primarily in tropical and sub-tropical countries, are at risk of contracting dengue. Nicknamed "break bone fever," classic dengue is characterized by high fever, headaches, muscle and joint pain, nausea, vomiting and a rash.
Some 50 to 100 million cases of debilitating dengue fever occur annually. The most severe form of the disease, dengue haemorrhagic fever, strikes half a million a year, according to the Centers for Disease Control and Prevention. Some 22,000 die of dengue haemorrhagic fever each year.
Morrison and Jeff Stancil, a U.S. Navy entomologist from the Naval Medical Research Center Detachment in Peru, were co-applicants on the grant.
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