Introducing birth control in mosquitoes

March 22nd, 2012
An Aedes aegypti mosquito prepares to bite a human. Credit: USDA.
Female mosquitoes require energy for their egg development, which they acquire from vertebrate blood. But by sucking on blood, they become vectors of numerous disease pathogens of human and domestic animals. If the mechanisms that govern their egg production are better understood, novel approaches to controlling the reproduction and population of mosquitoes can be devised.

Now a research team led by Alexander Raikhel, a distinguished professor of entomology at the University of California, Riverside, has received a five-year $2.8 million grant from the National Institutes of Health to study the molecular basis of hormonal regulation of mosquito reproduction.

The researchers will focus on deciphering the genes involved in mediating the action of hormones involved during egg production in mosquitoes — specifically, Aedes aegypti, the mosquito that spreads dengue and yellow fever.

"What we are setting out to do is introduce birth control, based on hormones, in mosquitoes," said Raikhel, an expert in the molecular biology of mosquitoes and a member of the National Academy of Sciences. "Our task is to find a way to interrupt the host-seeking behavior of mosquitoes by manipulating their hormones and thus interrupting their egg development. With egg development halted, the population of mosquitoes would eventually collapse."

Nearly 2.5 billion people are at risk for contracting dengue fever. Each year, there are 100 million cases of dengue in the world. Yellow fever results in 30,000 deaths per year; about 200,000 cases are reported each year.

Raikhel explained that a hormone unique to insects, called the "juvenile hormone," plays a key role in transforming a young female adult to a mature one that is capable of blood feeding, egg development, and thus spreading pathogens. The absence of this hormone in the body of the female mosquito impedes the growth of the mosquito to the adult stage. For the mosquito to reach the adult stage, levels of this hormone must first rise and then drop.

"This hormone is crucial for egg development," Raikhel said. "If we can figure out how its levels can be manipulated so that egg development is prevented, we can reduce the number of mosquitoes."

Each mosquito cell has a receptor for the juvenile hormone. The exact nature of this receptor, however, has eluded researchers for many years.

"In this project, we plan also to understand the structure and function of this receptor," Raikhel said. "One reason this receptor has been very difficult to study is that, unlike other receptors like it, it does not lie on the surface of the cell. Instead it lies inside the cell."

Raikhel's lab will attempt to block the action of the juvenile hormone's receptors.

"Several levels of interception can be designed in the lab so that no egg development in mosquitoes results," he said.

While his lab will focus in this project on only Aedes aegypti, the methods developed can be applied also to other disease-spreading mosquitoes.

Provided by University of California - Riverside

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