Disrupting a Delicate Balance
Invasive mosquitoes in Hawaiʻi transmit avian malaria and avian pox, causing severe declines in native forest bird populations. Rising temperatures from climate change allow mosquitoes to spread to higher elevations, exacerbating the problem. Conservation efforts, including innovative strategies like the Incompatible Insect Technique, aim to control mosquito populations and protect these endangered birds.
Images: Predator-proof fences on Hawaii’s isolated islands are vital for conserving native wildlife. These barriers, as seen in the steep terrain of Kauaʻi and other islands, prevent invasive species such as rats, cats, and mongoose from entering and disrupting the delicate ecosystems. By creating safe havens for native plants and animals, these fences play a crucial role in maintaining the unique biodiversity of Hawaii, which has evolved in isolation over millions of years. Conservation efforts like these are essential for preserving Hawaii’s natural heritage.
Invasive Mosquitoes Threaten Hawaiʻi’s Manu Nahele
Immediate Takeaways
Impact of Avian Malaria.
Threat of Avian Pox.
Climate Change and Mosquito Invasion.
Innovative Conservation Strategies.
Avian Malaria
Avian malaria is caused by the parasite Plasmodium relictum, which proliferates in the bloodstream of birds, leading to anemia, lethargy, and ultimately death. The disease is particularly lethal for Hawaiʻi’s endemic manu nahele (forest birds). In fact, if an ʻiʻiwi (Vestiaria coccinea) is bitten by a mosquito infected with malaria, there is a 90% chance it will die. Avian malaria is transmitted by the invasive southern house mosquito (Culex quinquefasciatus).
Culex quinquefasciatus
Photo: CDC, James Gathany
Kiwikiu Mortality
Photo: Bret Mossman
Avian Pox
Avian pox, a viral disease, manifests as tumor-like growths both inside and outside a bird’s body, often leading to discomfort, impaired vision, and difficulty feeding. The growths can be fatal, but even if they don’t cause death, they can leave birds vulnerable to starvation and predation. The pox virus is transmitted by mosquitoes or through direct contact with infected birds or contaminated surfaces.
It’s unclear how long avian malaria and avian pox have been present in Hawaiʻi. They may have been brought here by native migratory birds or with the many songbirds that were introduced by humans. In either case, the diseases didn’t pose a major threat to Hawaiian manu nahele because there wasn’t an effective vector to transmit them. That changed, however, in the 1800s.
Mosquitoes, which are not native to Hawaiʻi, spread the virus that causes avian pox. Symptoms of the disease include swollen, tumor-like lesions on unfeathered parts of a bird’s body, like the one on the right foot of this ʻamakihi (Chlorodrepanis virens). Lesions often cause birds to have difficulty with eating, finding food, and flying, leaving them vulnerable to starvation and predation.
Photo: Lauren Cassin Sackett
The importation of nonnative birds was encouraged, both for game hunting and agricultural pest control. By the 1920s, native landbirds had largely disappeared from lowland regions. Groups of Honolulu socialites, like the Hui Manu Society, responded to the lack of birds singing in their gardens by importing tens of thousands of songbirds from other parts of the world.
Introduced songbirds harbored nonnative diseases, including avian malaria and avian pox. Today, these deadly diseases, and the introduced mosquitoes that transmit them, pose the greatest threat to native Hawaiian manu nahele (forest birds). As the climate warms, mosquito populations are invading higher elevations, leaving less space for manu nahele to survive. As said in a famous Hawaiian ʻōlelo noʻeau (proverbial saying), ʻAʻohe kahua o nā manu—there is nowhere for the birds to land, crowded out of their homes and under threat of extinction. But hope is not yet lost.
Invasive mosquitoes
Mosquitoes were introduced to Hawaiʻi by humans and were well-established by the mid-1800s. They thrived in the warm, humid environment but couldn’t survive at higher elevations where cold temperatures prevented them from moving, feeding, and reproducing efficiently. Endemic manu nahele, already limited to high-altitude habitats to escape the mosquitoes, face severe declines as climate change allows the mosquitoes to invade higher elevations.
Having evolved without these diseases, honeycreepers have little natural immunity. This has resulted in the extinction of many species and left others critically endangered, disrupting the unique ecological balance of Hawaiʻi’’s forests and highlighting the urgent need for conservation efforts to control mosquito populations and protect these iconic birds.
Incompatible Insect Technique
The Incompatible Insect Technique (IIT) is an innovative pest control strategy that does not involve genetic modification. Rather, it leverages the biological incompatibility induced by the bacterium Wolbachia to suppress insect populations. In this method, male insects are infected with a specific strain of Wolbachia and released into the wild. When these infected males mate with wild females, the resulting eggs fail to hatch due to cytoplasmic incompatibility, effectively reducing the population over time. Unlike traditional chemical insecticides, IIT targets only the specific pest species, minimizing harm to other wildlife. This technique has shown promise in controlling disease vectors such as mosquitoes that spread dengue fever, Zika virus, and avian malaria, offering a sustainable and ecologically sensitive solution to managing insect-borne diseases.
To learn more about how IIT is being implemented in Hawaiʻi, please visit Birds Not Mosquitoes. Birds, Not Mosquitoes (BNM) is a coalition of state, federal, private, and non-profit partners. Their mission is to protect the native Hawaiian manu nahele by advancing efforts to suppress the non-native southern house mosquito population in high-elevation forests across the Hawaiian Islands.
Northern Cardinal
Native Landbirds
Avian Pox
