Mosquito control efforts in Alakaʻi Wilderness, Summer 2024

The Alaka’i Wilderness Preserve is home to unique and rare forest birds that are declining at alarming rates. Recent data show that ‘akikiki are extinct in the wild and ‘akeke’e and other honeycreeper species are reaching perilously low population numbers due to avian malaria carried by invasive mosquitoes. To control avian malaria, DLNR Forestry & Wildlife and the Kauaʻi Forest Bird Recovery Project are controlling mosquitoes over large areas of the Alakaʻi Wilderness. One approach involves aerial application of a highly mosquito-specific bacteria that controls mosquito larvae called Bti, derived from the bacterial strain Bacillus thuringiensis israelensis. Bti has been used for more than thirty years as an environmentally safe and effective larval control tool in sensitive habitats and even in organic agriculture. It only affects larvae of mosquitoes and close relatives such as blackflies and does not affect other insects, wildlife, or humans.

While Bti is often applied by hand to small water bodies while walking through a forested area, it would be impossible to cover enough area on foot to protect ʻakikiki and ʻakekeʻe habitat across the Alakaʻi Wilderness. Aerial application of Bti products has been used extensively for control of human disease, and this year we have successfully adapted this methodology for Hawaiian forest environments over a small pilot treatment area of 270 acres. Preliminary results show that droplets of Bti product applied from helicopter-mounted sprayers reach the forest floor in sufficient quantities to kill mosquito larvae. We have secured funds to expand the treatment area to ~1000 acres in the mid-Koaie drainage to provide more control of mosquitoes and avian malaria to protect forest birds from June 2024 through March 2025. Treatment will occur over several days for a couple of hours at dawn and dusk. Planned application dates are listed below, but are subject to change due to weather and other operational factors.

Bti is a different, complementary tool from the Incompatible Insect Technique, commonly known as mosquito birth control. IIT uses a different bacteria (Wolbachia) to reduce the amount of viable mosquito eggs produced in the wild. You can learn about different mosquito control tools and which are (and are not) used in Hawaiʻi from our partners at Birds Not Mosquitoes. You can also learn more about IIT and Wolbachia on our Mosquito FAQ page. You can also find additional information in this Bti FAQ produced by DLNR and Kauaʻi Forest Birds, or from this story on KITV.

Mosquito control efforts using IIT to begin in January of 2025

With climate change predictions, there is an urgency now to work with partners, like Birds not Mosquitos to find solutions that work for people, native forest birds, and Hawaii’s native ecosystems as a whole. Technologies have only recently been developed where control could be addressed at larger scales. These technologies include the use of Wolbachia, a naturally occurring bacteria that could be used as mosquito birth control. Wolbachia have been used successfully in other parts of the world as illustrated by this video. Please refer to the video below to see how Wolbachia may work to control mosquitos in Hawaiʻi.

The Incompatible Insect Technique (IIT) uses Wolbachia, a naturally-occurring bacteria to help suppress mosquito populations. This approach takes advantage of the fact that mosquitoes with different, incompatible strains of Wolbachia can’t produce viable offspring. Male mosquitoes with one strain of Wolbachia can only reproduce with females with a compatible strain of Wolbachia. Conversely, males with one strain of Wolbachia cannot produce viable offspring with females that have a different, incompatible strain of Wolbachia.

For this project, egg rafts of the southern house mosquito were collected from Hawaiʻi and sent to a facility on the U.S. continent. In a laboratory setting, researchers transfered an incompatible strain of Wolbachia into the mosquitoes, then reared large numbers of them. Once separated by sex, only male mosquitoes (which do not bite) are transported from the rearing facility and released back into mosquito breeding grounds in Hawaiʻi to mate with wild females. The development and production of incompatible males is done in a facility on the U.S. continent because Hawaiʻi doesn’t currently have a facility for producing large amounts of incompatible male mosquitoes.

When the released Wolbachia-incompatible male mosquitoes mate with wild females, the females lay eggs that never hatch. With consecutive releases, mosquito populations decrease because no new generations are produced. Fewer mosquitoes is great for our birds! The decrease in mosquito populations means that there will be fewer mosquitoes that are able to transmit fatal avian malaria to our endangered honeycreepers. 

Mosquito Sampling-Photo by Theo Black