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February 28, 2024

Biologists from the U.S. Geological Survey are racing the clock to pull four species of native Hawaiian Honeycreeper forest birds back from the brink of extinction.  

Factors such as habitat loss, invasive species, and non-native predators have been fueling the birds’ decline for centuries. However, introduced diseases, particularly avian malaria spread through mosquitoes, which are not native to the Hawaiian Islands, coupled with climate change, are the greatest threat facing Hawaiian forest birds today. 

“As the climate warms and more mosquitoes move into the once malaria-free regions of the mountains, healthy birds are running out of places to escape the cycle of infection,” said Eben Paxton, a research ecologist with the USGS Pacific Island Ecosystems Research Center (PIERC) in Hawai‘i. 

Image: An Endangered Honeycreeper, the  ‘Akeke‘e (Kaua‘i Akepa), in Hawai‘i

Now, PIERC biologists are working with a range of partners, including other Interior Department bureaus and the Birds Not Mosquitoes Coalition, to intercept the disease cycle using a novel conservation tool.

Dr. M. Renee Bellinger, a PIERC research geneticist, explained how they are utilizing mosquito control through the Wolbachia Incompatible Insect Technique (ITT).  

Wolbachia is a naturally occurring bacteria found in some insects, including mosquitoes, that can be used to alter the reproductive capabilities of their host.   

“The Wolbachia method operates to control mosquito populations through mating of males and females that carry incompatible strains of the bacteria, which stops eggs from developing,” said Bellinger. 

How it works is biologists transfer an incompatible Wolbachia strain into mosquitoes raised in a controlled environment, then select only males for release into the wild. Because male mosquitoes do not bite birds or humans, they have no impact other than serving as a conduit to blocking mosquito reproduction in the specified environment. Once the transinfected males mate with wild females, their eggs will be nonviable and unable to hatch.   

Essentially, it’s a natural form of mosquito birth control.  

According to Bellinger, this Wolbachia technique has been used to control mosquito populations since the 1960’s, as well as to manage the spread of diseases such as Dengue and yellow fever. However, efforts in Hawai‘i will be the first time the method could be used to mitigate avian malaria, as well as the first time the method will be used for large-scale conservation. 

Getting to this point, Bellinger said, was no small feat. While the technology to control Wolbachia previously existed, it hadn’t been developed for the specific type of mosquito currently plaguing the Hawaiian landscape.   

“To get the exact product we needed, we first needed to develop it,” said Bellinger. 

In this case, scientists were looking at Culex, a genus of mosquito known to carry avian malaria.  

Culex mosquito eggs are viewed under a mircroscope

Still, researchers had to dial in further to determine the exact type of Culex surviving on the Hawaiian archipelago, how the insects impact avian malaria and vice versa, and quantify how likely they are to serve as a vector of the disease.  

In a California laboratory, Bellinger said scientists have been raising tens of thousands of male mosquitoes with a Wolbachia strain that is incompatible with the Culex that invaded Hawai'i. Releases of lab-reared males into the Maui landscape began in November 2023 via biodegradable pods. The pods are deployed from helicopters, over areas most critical to the forest birds.  

Now, scientists will monitor the results; working to recapture the mosquitoes to see how the controlled males are faring, and how future batches can be adjusted by utilizing Bipartisan Infrastructure Law (BIL) funds to support the data acquisition.  

Simultaneously, Paxton and his colleagues will conduct field projects to study future impacts on the Honeycreepers, looking for patterns of the avian malaria and disease dynamic cycle.  

“We’re running two races against the same clock: a sprint and a marathon,” said Paul Heimowitz, the Terrestrial Invasive Species Program manager for the USGS Ecosystems Mission Area. “We’re working fast to prevent imminent extinction of the forest birds by controlling the disease at the source. Meanwhile, the long-term goal is to eradicate Culex mosquitoes from the Hawaiian Islands altogether,” he said.   

Image: An Endangered Honeycreeper, the `Akikiki (Kaua`i Creeper), in Hawaii

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