Biological control is the management and control using biological means.
Natural predation '' (Mosquitofish), a natural mosquito predator. , custom-built to house bats for biocontrol of mosquitos
Biological pest control, or "biocontrol", is the use of the natural predators of pests like mosquitoes to manage the pest's populations. There are several types of biocontrol, including the direct introduction of parasites, pathogens, and predators to target mosquitoes. Effective biocontrol agents include predatory fish that feed on mosquito larvae such as
mosquitofish (
Gambusia affinis) and some
cyprinids (carps and minnows) and
killifish.
Tilapia also consume
mosquito larvae. Direct introduction of tilapia and mosquitofish into ecosystems around the world have had disastrous consequences. However, utilizing a controlled system via
aquaponics provides the mosquito control without the adverse effects to the ecosystem. Other predators include dragonfly (fly)
naiads, which consume mosquito larvae in the breeding waters, adult
dragonflies, which eat adult mosquitoes, and some species of
lizard and
gecko. Biocontrol agents that have had lesser degrees of success include the predator mosquito
Toxorhynchites and predator
crustaceans—
Mesocyclops copepods,
nematodes and
fungi. Predators such as birds, bats, lizards, and frogs have been used, but their effectiveness is only anecdotal.
Biocides Instead of chemical insecticides, some researchers are studying biocides. Like all animals, mosquitoes are subject to disease. Invertebrate pathologists study these diseases in the hope that some of them can be utilized for mosquito management. Microbial pathogens of mosquitoes include viruses, bacteria, fungi, protozoa, nematodes and microsporidia. Most notably, scientists in
Burkina Faso were studying the
Metarhizium fungal species. This fungus in a high concentration can slowly kill mosquitoes. To increase the lethality of the fungus, a gene from a spider was inserted into the fungus causing it to produce a
neurotoxin. The gene was regulated to only activate when in mosquito hemolymph. Research was done to show the fungi would not affect other insects or humans. Two other species of fungi that can kill adult mosquitoes are
Metarhizium anisopliae and
Beauveria bassiana. Dead spores of the
soil bacterium Bacillus thuringiensis, especially
Bt israelensis (BTI) interfere with
dipteran larval
digestive systems. It can be dispersed by hand or dropped by
helicopter in large areas. BTI loses effectiveness after the larvae turn into pupae, because they stop eating. BTI was reported to be widely applied in West Africa with limited adverse effects, and may pose lesser risk than chemical pesticides.
Wolbachia method In the
Wolbachia method, both male and female mosquitos that carry the
Wolbachia bacterium are released into natural populations.
Wolbachia boosts the natural immune response of the mosquito so that it does not easily get infected and become a host vector for mosquito-borne diseases. Therefore it is unable to easily transmit those viruses to people. This is known as replacement strategy as it aims to replace the natural population with
Wolbachia-carrying ones. Since 2011, the
World Mosquito Program has conducted several trials and projects, in 14 countries across Asia, Latin America and Oceania. In a cluster-randomized trial in Yogyakarta, Indonesia, release of Wolbachia-infected Aedes aegypti mosquitoes was associated with a 77% reduction in dengue incidence compared with control areas (Utarini et al., 2021).
Incompatible Insect Technique (IIT) This approach also uses
Wolbachia but involves the release of only male mosquitos that carry the
Wolbachia bacterium. When these male mosquitos mate with wild female mosquitos, her eggs do not hatch due to lack of biocompatibility.
Wolbachia is not endemic to wild mosquito populations although it is endemic in 50% of all insect species. This is known as suppression strategy as it aims to suppress the natural reproduction cycle.
Wolbachia-Aedes suppression has been piloted in various countries such as Myanmar (1967), French Polynesia (2009, 2012), USA (2014-2016, 2018), Thailand (2016), Australia (2017), Singapore (since 2016) and Puerto Rico (2020).
Projects Maui and Kuai, Hawaii - A series of IIT projects were planned to protect endangered bird species from
avian malaria. The projects involve the release of large numbers of male mosquitos infected with a strain of
Wolbachia that is incompatible with the strain carried by resident females. These mosquitos would not be irradiated or subject to genetic modification.
Sterile Insect Technique (SIT) Introducing large numbers of sterile males is another approach to reducing mosquito numbers. This is called
Sterile Insect Technique (SIT). Radiation is used to disrupt DNA in the mosquitoes and randomly create mutations. Males with mutations that disrupt their fertility are selected and released in mass into the wild population. These sterile males mate with wild type females and no offspring is produced, reducing the population size.
Projects Guangzhou, China - A combination of SIT with IIT, were used in a mosquito control program in Guangzhou, China. The pilot trial was carried out with the support of the
IAEA in cooperation with the
Food and Agriculture Organization of the
United Nations (FAO). The pilot demonstrated the successful near-elimination of field populations of the world's most invasive mosquito species,
Aedes albopictus (Asian tiger mosquito). The two-year trial (2016–2017) covered a 32.5-hectare area on two relatively isolated islands in the
Pearl River in Guangzhou. It involved the release of about 200 million irradiated mass-reared adult male mosquitoes exposed to
Wolbachia bacteria. The trial reported that this combined incompatible and sterile insect technique nearly eliminated local Aedes albopictus populations on the treated river islands ==Genetic modification==