Hawaii's Unlikely Heroes: Swarms of Mosquitoes Combat Avian Decline

In 1826, mosquitoes arrived in Hawaii and pushed native birds toward extinction. Now, scientists are releasing millions of mosquitoes to save them

Hawaii's native birds face extinction due to avian malaria transmitted by mosquitoes. Conservationists are releasing sterile male mosquitoes to reduce disease-carrying populations. This innovative strategy aims to protect honeycreeper species from the deadly infection.

The problem started with an introduced mosquito

Hawaii's honeycreepers evolved in isolation for millions of years, producing dozens of distinct species. The i'iwi, known for its bright scarlet plumage and distinctive bill, is one example of this evolutionary diversity. But that diversity has declined dramatically.

The mosquito that transmits avian malaria and the organism responsible for the disease are both non-native to Hawaii. As a result, many endemic birds have little immunity to the infection.

For years, elevation provided some protection. Mosquitoes struggle to survive in colder conditions, allowing some honeycreepers to persist in forests at elevations of roughly 4,000 to 5,000 feet. These areas became important refuges for birds that had lost much of their lower-elevation habitat.

Climate change is now threatening those refuges.

As temperatures increase, mosquitoes are able to move farther upslope, entering areas that previously remained too cold for them. Conservationists have observed mosquitoes invading habitats that once provided some of the last remaining safe areas for native birds.

A mosquito solution to a mosquito problem

The current strategy involves releasing large numbers of laboratory-reared male mosquitoes. The males do not bite. Instead, their role is reproductive.

The mosquitoes are associated with a technique known as the incompatible insect technique, which uses different strains of the naturally occurring bacterium Wolbachia. When a male carrying one strain mates with a female carrying an incompatible strain, the resulting eggs do not hatch.

Because female mosquitoes generally mate only once, mating with one of these incompatible males can prevent her from producing viable offspring. The objective is to gradually reduce the number of mosquitoes capable of transmitting avian malaria.

So far, about 10 million male mosquitoes have been released by helicopter into high-elevation forests on Maui. The insects are transported in cardboard tubes before being released in areas where endangered birds are still found. The approach requires repeated releases because mosquitoes live only a few weeks. Maintaining the suppression effort therefore requires continued funding and regular operations in remote forest areas.

The broader conservation coalition behind the effort, Birds, Not Mosquitoes, describes the strategy as an attempt to address an extinction crisis that is becoming more difficult to manage as temperatures rise.

The birds are already close to disappearing

The scale of the crisis can be seen in the populations of individual species. The 'akikiki, a small Hawaiian honeycreeper, has declined from a wild population of more than 1,000 birds about 15 years ago to an estimated two to five birds in the wild. More than 40 are held in captivity, where conservationists operate a carefully managed breeding program.

The kiwikiu, also known as the Maui parrotbill, is another species in rapid decline. Only about 100 were estimated to remain in the wild when the source material was compiled. Conservationists spent more than a decade restoring habitat for the species, including planting tens of thousands of trees.

But even restored habitat has not necessarily remained safe. In 2019, 14 kiwikiu were released into a new reserve. Within weeks, almost all died after unusually hot weather allowed mosquitoes to move into the area and spread avian malaria.

Scientists are also studying genetically modified mosquitoes

Wolbachia-based strategy is not the only technology being investigated. Scientists are researching whether mosquitoes could eventually be genetically modified so that they can no longer transmit avian malaria.

One proposed approach involves inserting a gene that prevents the Plasmodium parasite from completing its life cycle inside the mosquito. Researchers describe this as a gene drive, a form of genetic modification designed to increase the likelihood that a particular genetic trait will be inherited by offspring.

Researchers say genetically modified mosquitoes remain at an early research stage. They say such mosquitoes could be years away from any potential release, and any proposed release would face significant regulatory requirements.