Larvicides

Targeting the breeding sites of mosquitoes is generally an attractive option for control. This is because a relatively large number of larvae will be present within a much smaller area, compared to the much larger treatment area for flying adults.

All mosquitoes must have water in which to complete their lifecycle, however not all mosquitoes prefer the same conditions. Some mosquito larvae develop in polluted or brackish water environments and some prefer cleaner water. Other species prefer to lay their eggs on small water bodies (e.g. puddles, hoof prints or in small containers. The type and number of breeding sites within any given area is a good indication of the types of vectors which may be present (and how abundant they are).

This diversity of breeding preferences can be well illustrated by considering two important vector genera such as Anopheles (a genus which contains the malaria vectors) and Aedes (containing the major vectors of dengue and yellow fever):

• Most species of Anopheles prefer clean, unpolluted water and larvae have been found in fresh or salt-water marshes, mangrove swamps, rice fields, grassy ditches, the edges of streams and rivers, and small, temporary rain pools. Many species prefer habitats with vegetation and others prefer habitats that have none. Some breed in open, sun-lit pools while others prefer shaded breeding sites in forests, tree holes or the leaf axils of some plants.
• The major vector species within the genus Aedes (Aedes aegypti and Aedes albopictus) are recognised as container-breeding species. These prefer small volumes of water (artificial or natural) and encompassing environments like rainwater in used tires, discarded tins and plastic containers, abandoned car parts, water-collecting trays under plant-pots and natural situations such as the water collected in dead leaves, tree holes, and rock pools.

Breeding sites can be targeted either through engineering initiatives (e.g. drainage schemes), improved sanitation (e.g. removal of debris which can catch rainwater) or through specific targeting with mosquito larvicides. In many situations, it is necessary to combine some of these methods for an integrated approach. The diversity in breeding site preferences between species can present a challenge for effective implementation, especially where mixed species are present.

Learn more about the larvicides available from Bayer. To find out about products available in your country, contact your local Bayer expert