Biological control is based on the introduction of organisms that prey upon, parasitize, compete with or otherwise reduce populations of the target species. Against Aedes, a selection of larvivorous fish species and predatory copepods (small freshwater crustaceans) are effective against the immature larval stages of vector mosquitoes.
The biological control organisms are bred and distributed into water-storage containers or wells. Small-scale projects have shown that the success of biological control is mainly reliant on the organization of the project:
- Breeding of fish/copepods;
- Community mobilization and participation (willingness to accept the introduction of organisms into water containers);
- Distribution system for fish/copepods (regular restocking and monitoring).
A variety of fish species have been used to eliminate mosquitoes from larger containers used to store potable water in many countries, and in open freshwater wells, concrete irrigation ditches and industrial tanks. Commonly, guppies adapt well to these types of confined water bodies and have been most commonly used. Only native larvivorous fish should be used because exotic species may escape into natural habitats and threaten the indigenous fauna. WHO has published further information on the use of fish for mosquito control.
More information is available from the WHO:
- Standard Operating Procedures on breeding and dissemination (click here)
- WHO Use of fish in mosquito control (click here)
Various predatory copepod species (small crustaceans) have also proved effective against dengue vectors in operational settings. However, although copepod populations can survive for long periods, as with fish, reintroductions may be necessary for sustained control. A vector control programme in northern Viet Nam using copepods in large water-storage tanks, combined with source reduction, successfully eliminated Ae. aegypti in many communes and has prevented dengue transmission for a number of years. To date, these successes have not been replicated in other countries.