Division of Forestry and Wildlife

Project description

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 nearly 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 30 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 commonly applied by hand to small water bodies during ground-based surveys, this approach cannot cover sufficient area to protect ʻakikiki and ʻakekeʻe habitat across the Alakaʻi Wilderness. Aerial application of Bti has been used extensively for mosquito control targeting human disease, and this methodology was adapted in 2023 for Hawaiian forest environments during a pilot treatment covering 270 acres. Preliminary results demonstrated that droplets of Bti applied from helicopter-mounted sprayers successfully reached the forest floor in quantities sufficient to kill mosquito larvae. Additional funding was then secured to expand treatment to approximately 1,000 acres in the mid-Koaie drainage to enhance mosquito and avian malaria control for the protection of native forest birds. Bti treatments in the mid-Koaie drainage were conducted from June 2024 through June 2025. 

In December 2025, aerial applications resumed over approximately 2,100 acres across the southern Alakaʻi plateau (see map below). Currently, treatments are scheduled to occur every other Monday between 7:00 a.m. and 4:00 p.m. In the event of cancellations, backup flights will be conducted the following Monday. Planned application dates are listed below but are subject to change due to weather conditions 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 find additional information in this Bti FAQ produced by DLNR and Kauaʻi Forest Birds, or from this story on KITV. 

Currently planned application dates (subject to change due to weather or other factors)