Source Reduction

Source  reduction is removal or permanent  destruction of mosquito breeding sites. The larval habitats may be destroyed by  filling depressions that collect water, by draining swamps, or by ditching  marshy areas to remove standing water. Container-breeding mosquitoes are  particularly susceptible to source reduction as people can be educated to  remove or cover standing water in cans, cups, and rain barrels around houses.  Mosquitoes that breed in irrigation water can be controlled through careful  water management.

For some mosquito species, habitat elimination  is not possible. For these species, chemical insecticides can be applied  directly to the larval habitats. Other methods, which are less disruptive to  the environment, are usually preferred:

  • Oils  may be applied to the water surface, suffocating the larvae and pupae. Most  oils in use today are rapidly biodegraded.
  • Toxins  from the bacterium Bacillus thuringiensis var. israelensis (Bti) can be  applied in the same way as chemical insecticides. They are very specific,  affecting only mosquitoes, black flies, and midges.
  • Insect  growth regulators such as methroprene are specific to mosquitoes and can be  applied in the same way as chemical insecticides.
  • Potential  biological control agents, such as fungi (e.g., Laegenidium giganteum) or mermithid nematodes (e.g., Romanomermis culicivorax), are less  efficient for mosquito control and are not widely used. Likewise, mosquito fish  (including Gambusia affinis)  have largely been ineffective except in a few studies.

Theoretically, it seems that source reduction would  be an ideal approach to mosquito control: eliminate mosquitoes before they  reach the stage where they can transmit malaria.  However, larval habitats may be small, widely  dispersed, and transient. Anopheles gambiae,  one of the primary vectors of malaria in Africa, breeds in numerous small pools  of water that form due to rainfall. The larvae develop within a few days,  escaping their aquatic environment before it dries out. It is difficult, if not  impossible, to predict when and where the breeding sites will form, and to find  and treat them before the adults emerge. Therefore, larval mosquito control for  the prevention of malaria in Africa has not been attempted on a large scale.

More information available at Center for Disease Control and Prevention (