Malaria.com

Mosquito Larvae Eradication

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QUESTION

What measures can be taken to eradicate mosquito larvae?

ANSWER

The main methods to control mosquito larval populations are by reducing areas available for adults to breed and also directly killing larvae. So, for example, adult mosquitoes need standing, stagnant water in order to lay their eggs. Getting rid of these sources of standing water, for example by filling in unwanted ditches and removing empty containers that can become filled with rainwater, therefore reduces the available breeding habitat for mosquitoes. Similarly, dripping a small amount of oil on top of standing water creates a thin film of oil over the surface of the water, preventing adults from laying eggs. In addition, the oil prevents the larvae from gaining access to air, suffocating them and killing them. There are other methods for killing larvae too. Directly spraying insecticides onto water is one method, but often not very specific, and can have a negative effect on other forms of aquatic life. One popular method for biocontrol is to introduce other animals which eat mosquito larvae, thus keeping numbers down. Examples include certain species of fish, as well as small crustaceans called copepods.

Use of Fish for Malaria Eradication

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QUESTION

Why is very little research being done on the possibility of mosquito fish being used as a means of controlling the hatching of new eggs?

ANSWER

Actually there is a lot of scientific literature on the use of fish as a biological control of mosquitoes, usually through consumption of the mosquito larvae or pupae while they are in freshwater. The most common species used for this purpose are the guppy (Poecilia reticulata) and the appropriately named mosquito fish (Gambusia affinis). Other fish groups, like cyprinodontids (i.e. Aphanius species), tilapia and minnows will also eat mosquito larvae.

In addition, other freshwater predators, such as copepods, have been shown to be highly effective in  killing mosquito in laboratory and field experiments, though results are sometimes inconsistent (see Lardeaux, 2008 “Biological control of Culicidae with the copepod Mesocyclops aspericornis and larvivorous fish (Poeciliidae) in a village of French Polynesia,” in Medical and Veterinary Entomology, vol 6, issue 1, pages 9-15, for a comparison of the anti-mosquito effect of these different groups).

The Lardeaux paper also describes the failure of the program: despite introduction of larvivorous animals, biting rates of mosquitoes did not significantly reduce, indicating some of the complications that can be associated with biological control programs.

However, in Vietnam, field studies have shown significant reductions of local Aedes mosquitoes associated with the presence of copepods in standing water sources, which shows the potential positive effects of incorporating natural biological control agents within part of an integrated vector control strategy (Nam et al., 2000 “National progress in dengue vector control in Vietnam: Survey for Mesocyclops (Copepoda), Micronexa (Corixidae) and fish as biological control agents,” in the American Journal of Tropical Medicine and Hygiene, vol 62, issue 1, pages 5-10).

Another example of successful introduction of fish as biological control agent comes from Ethiopia (Fletcher et al., 1992 “Control of mosquito larvae in the port city of Assab by an indigenous larvivorous fish, Aphanius dispar,” in Acta Tropica, vol 52, issue 2-3, pages 155-166).