Conservationists on Kauai have begun releasing hundreds of thousands of male mosquitoes incapable of reproducing in an effort to combat avian malaria, a disease threatening native honeycreepers with extinction.

The Kauai Forest Bird Recovery Project on Thursday released the first batch of mosquitoes into a state forest reserve on the Alakai Plateau following a decade of planning, permitting and community outreach.

Using “incompatible insect technology,” or IIT, the effort aims to suppress mosquito populations by introducing males that cannot successfully reproduce with wild females, according to the state Department of Land and Natural Resources. Because only female mosquitoes bite and transmit avian malaria, reducing their numbers could help protect honeycreepers such as the akikiki and akekee, whose populations are critically low.

“The idea is that you release male mosquitoes which do not bite onto the landscape that are reproductively incompatible with the wild females that are on the landscape, and because they’re incompatible, when they meet, the eggs aren’t fertilized, and therefore they don’t hatch and we don’t have the next generation of mosquitoes,” KFBRP Program Manager Lisa Crampton said. “So it leads to mosquito population suppression, and by reducing the populations of mosquitoes on the landscape, we hope that we will reduce the amount of avian malaria, which is driving the forest bird declines on the landscape.

IIT has been widely used to combat human malaria, but this marks its first deployment on Kauai to target mosquitoes carrying avian malaria.

“It is a tried and true technique that has been used across multiple jurisdictions globally to suppress mosquitoes that transmit human health diseases,” Crampton said.

The mosquitoes are bred at a facility in California and transported to Kauai, where approximately 500,000 are being released each week. They are distributed via helicopter using biodegradable tubes designed to disperse the insects evenly across the landscape.

The mosquito control efforts are part of an integrated pest management strategy that includes the use of a larvicide known as BTI, which targets mosquito larvae. The larvicide has been applied on the Alakai Plateau for nine years and, more recently, from helicopters.

“So we think about this as integrated pest management, where BTI targets one phase of the mosquito lifestyle, the larval phase, and the IIT targets the adult stage and the, you know, the egg production stage,” Crampton said. “The idea is that BTI reduces populations of adults to begin with, making it more likely that these males will encounter a female or the female will encounter one of these incompatible males. And conversely, the fact that we are producing fewer and fewer viable eggs means that the BTI will be targeting only a few larvae down there and hopefully we’ll be able to apply BTI at greater integrals because there will be much lower production. So the two tools really do work hand in hand to control mosquito populations.”

Crampton emphasized the urgency of the effort, pointing to the dire situation of several honeycreeper species. Fewer than 20 akikiki remain in the wild. A captive breeding program in collaboration with San Diego Zoo Wildlife has successfully maintained a flock of 40 birds, providing hope for the species’ future.

Crampton also said the akekee population is critically low, with potentially fewer than 50 individuals remaining. The next species of concern is the anianiau, which is also found only on Kauai. With a population of around 3,000, the species has seen a 65% decline over the past five years.

Other species, such as the Kauai amakihi, have remained stable at around 10,000 individuals for over the last decade.

Conservationists are hopeful that after a year of IIT and BTI efforts, birds currently in breeding programs or their offspring may be reintroduced to the wild.

“It is, for sure, our hope that we will be able to release birds back onto the landscape once we have done this IIT suppression work and the BTI mosquito suppression work for a year or so, continuously over that part of the Southern Alakai Plateau, which is the best forest bird habitat that we know of on Kauai,” Crampton said. “So we are very hopeful that that will be the future of these birds that are in conservation breeding programs, that if not them, then their offspring will one day be released back into the wild.”