Genetic discovery could spell death knell for mosquitoes

In 2018, contrary to generally accepted scientific wisdom, UCR entomologist Naoki Yamanaka found that an important steroid hormone requires transport proteins to enter or exit fruit fly cells. The hormone, ecdysone, is called the ‘moulting hormone’. Without it, flies will never mature or reproduce.

Before its discovery, textbooks taught that ecdysone travels freely through cell membranes and slides along easily. “We now know that’s not true,” Yamanaka said.

Every insect species needs ecdysone for some aspect of their journey from egg to progeny-producing adult. And every insect Yamanaka has tested also possesses the ecdysone transporter he found in 2018, plus a few more found in a new study. But in this new study, Yamanaka found that mosquitoes are different.

Mosquitoes have only three of the four transport proteins that fruit flies possess. They lack the main, primary ecdysone transporter.

“This primary is somehow, mysteriously, missing in mosquitoes,” Yamanaka said.

These findings are now published in the Proceedings of the National Academy of Sciences.

The discovery opens the door to a mosquito-specific insecticide that would not harm beneficial bees or other pollinators. However, it would affect mosquitoes such as the mosquitoes used in the study, Aedes aegypti, which spread Zika, dengue, yellow fever, chikungunya and other viruses.

“We can develop chemicals to block the functions of these ecdysone transporters, but not affect the original transporter that is so important to other insects,” Yamanaka said. “The probability of off-target effects would be low.”

A related UC Riverside study, led by cell biologist Sachiko Haga-Yamanaka, is trying to pinpoint similar hormone-transporting machinery in humans.

“Textbooks state that steroid hormones can be freely transported in and out of human cells, but based on our insect research, we doubt that is the case,” Yamanaka said.

Yamanaka’s research is funded by the National Institutes of Health. His lab is now screening for chemicals that can block mosquitoes’ ecdysone importers. He also conducts research into ecdysone transporters in other animals.

However, other methods exist to ensure that local mosquito populations cannot reproduce. Releasing sterile, irradiated male mosquitoes into the wild to mate with females results in eggs that do not hatch, a technique that eliminates the need for insecticides.

While there are effective methods such as these to control local mosquito populations, Yamanaka believes it is important to develop additional tools so that we can address mosquito-related problems in many different scenarios.

“It’s impossible to let mosquitoes die out,” Yamanaka said. ‚ÄúDepending on one tool to keep them under control is dangerous. As the climate warms, it creates even more favorable conditions for them to multiply, and they will likely only become a bigger problem, especially in Southern California.”

To access the UCR story and photos, click here.

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