(BIVN) – The State of Hawaiʻi is moving forward with a plan to release sexually incompatible mosquitoes in the hopes of reducing disease-spreading mosquito populations in the islands.
On May 9, 2022, the Hawaiʻi Board of Agriculture gave preliminary approval to add three mosquito species to the List of Restricted Animals: the Asian tiger mosquito (Aedes albopictus), the yellow fever mosquito (Aedes aegypti), and the southern house mosquito (Culex quinquefasciatus).
In April 2022, the Hawaiʻi Department of Agriculture’s Plant Quarantine Branch received a permit application from the Hawaiʻi Department of Health and the Hawaiʻi Department of Land and Natural Resources, requesting that the state ag board add the three mosquitos to the list.
Officials say they need to list the mosquitos “for immediate field release applications to suppress mosquito populations in areas where Hawaii residents are at risk of disease transmission due to the presence of these mosquitoes.” Mosquito-born disease is also a threat to the endangered native birds of Hawaiʻi.
From the health department document:
As outlined in the suggested conditions for importation, these mosquitoes will either contain the same wild type bacterium (Wolbachia spp.) which is already endemic in the three mosquitoes in Hawaii, or will be inoculated with an incompatible bacterium (Wolbachia spp.) that is not native to the wild mosquito’s current internal fauna. The presence of this different strain of bacteria within the male mosquito’s reproductive system will render the imported male mosquitoes unable to successfully mate with wild females found within Hawaii, a process called cytoplasmic incompatibility. Cytoplasmic incompatibility has been used with much success in other parts of the world to reduce mosquito populations and thus reduce the potential of transmission of mosquito vectored diseases. We intend to import male, sexually incompatible mosquitoes for direct release onto the environment. This process uses cytoplasmic incompatibility to reduce current populations of these species, which are potential vector of human pathogens including Zika virus, dengue virus, chikungunya virus, yellow fever virus, West Nile virus, and lymphatic filariasis. Additionally, these mosquito species arevectors for pathogens to Hawaii’s fauna, including pathogens such as avian malaria, avian pox, and dog heartworm. Importing Hawaii lineage mosquitoes which contain the wild type bacterium, will ensure that we can conduct genetic analysis to confirm that the wild Culex quinquefasciatus is the wild type originally provided to the collaborators, and that the inoculated mosquitoes are indeed incompatible.
These three species are invasive, disease-spreading mosquitoes that can be found throughout Hawaii. These species were introduced accidentally to Hawaii in either the 1800s or early 1900s. Aedes albopictus and Aedes aegypti are known vectors of arboviral pathogens such as Zika virus, dengue virus, yellow fever virus, and chikungunya virus. These species are believed to have been the primary vectors during Maui’s 2001 dengue virus outbreak, Oahu’s 2011 dengue virus outbreak, and Hawaii County’s 2015-2016 dengue outbreak, which led to more than 264 cases of the illness. Culex quinquefasciatus is also a mosquito species of public health concern as it is known to vector West Nile virus on the US mainland and lymphatic filariasis in other Pacific nations. The species is present on Hawaii, Maui, Molokai, Lanai, Kahoolawe, Oahu, Kauai, and the northwest Hawaiian islands. Culex quinquefasciatus can thrive at sea-level to 4800ft in elevation. In Hawaii, these species are also able to transmit pathogens to Hawaii’s native forest birds. Culex quinquefasciatus is a known vector of avian malaria and Aedes albopictus is a vector of avian pox. These diseases have contributed to the extinction of more than half of Hawaii’s endemic honeycreepers and continue to pose a risk to the remaining species. Lastly, these mosquito species are known to transmit dog heartworm within pets found throughout Hawaii.
Efforts to suppress these mosquitoes through utilization of traditional vector control methods (e.g., pesticides) are inadequate at a landscape scale, and may be problematic for other non-target state and federally protected invertebrate species including Hawaiian picture-wing flies (Drosophila spp.), damselflies (Megalagrion spp.), yellowfaced bees (Hylaeus spp.) and anchialine pond shrimps (Vetericaris chaceorum and Procaris hawaiana). Current efforts to control mosquito-vectored disease outbreaks are limited to reducing mosquito breeding site locations and localized applications of various larvicides and adulticides.
On September 6-7, 2016, local, national, and international experts gathered in Hawaii to discuss how to mitigate mosquito-borne diseases. The strategy deemed most favorable in terms of its effectiveness, technical readiness, and safety was Wolbachia-based cytoplasmic incompatibility. Cytoplasmic incompatibility results from the presence of a bacterium, Wolbachia, in the cells of the mosquito. Many arthropod species, including several native species here in Hawaii, naturally contain strains of Wolbachia. Bacteria in the genus Wolbachia are a type of arthropod endosymbiont that do not occur in humans or other vertebrates. Approximately 50% of insect species naturally have the bacteria, although many of these insects can survive without Wolbachia. Conversely, Wolbachi cannot persist outside of insect cells, as it is an obligate endosymbiont. The largest effect of Wolbachia is on mating compatibility between individual insects that carry the bacteria. However, there are secondary effects that are being studied by many labs. These include altered host insect lifespan and reduced vector competence.
In nature, Wolbachia are passed from females to their offspring. Different strains of Wolbachia have also been introduced into insects in laboratories. If a male mosquito with one type of Wolbachia mates with a female mosquito that has a different strain of Wolbachia the resulting offspring can be inviable and not develop into mosquito larvae because of a mismatch of cellular signals (loss of the male parental chromosomes) originating from Wolbachia. If sufficient numbers, on the order to 10 times the wild population size, of male mosquitoes of a different Wolbachia type are released, wild females are more likely to mate with males of a different Wolbachia type and are predicted to have far fewer viable offspring. With subsequent releases, this process can significantly suppress the wild population numbers of mosquitoes over the following generations over a geographic area. Wolbachia male-based insect control programs have been highly successful for reducing local mosquito populations around the world. Results of initial trials in Fresno, California showed decrease of biting Ae. aegypti females by 68%, 95%, and 84% during the peak mosquito seasons in 2017, 2018, and 2019 respectively. Wolbachia cannot be spread by the released males, because Wolbachia are only passed from mother to offspring. It is also worth noting that male mosquitoes do not bite or vector disease.
One way to generate mosquitoes with a different Wolbachia type, is by clearing the naturally-occurring Wolbachia strain from the mosquitoes using the antibiotic tetracycline. Then Wolbachia can be harvested from cells of another insect species (this can be another mosquito or a non-mosquito species) and introduced into the cleared mosquitoes via microinjection. Another method to establish new Wolbachia strains is to mate a Wolbachia-carrying female insect to males that have been cleared of their naturally-occurring Wolbachia via antibiotic treatment. Because Wolbachia are maternally inherited (described above), this cross results in all of the offspring inheriting whichever Wolbachia strain is contained in the female parent. Incompatible Wolbachia strains can also be naturally present in populations of mosquitoes.
The Hawaiʻi Department of Agriculture says the Plant Quarantine Branch will be soliciting comments on the proposal until June 8, 2022.
Comments may be sent to Mr. Jonathan Ho, Inspection and Compliance Section Chief via:
- Email: Jonathan.K.Ho@hawaii.gov
- Phone: (808) 832-0566
- Fax: (808) 832-0582