Larvicides

Larvicides are substances used to kill the larval stages of insects, particularly species that breed in aquatic habitats such as mosquitoes, flies, and midges. They are applied to water bodies or other larval habitats to prevent development into flying adults, contributing to pest control and disease prevention in vector management programs. Larvicides can be chemical, biological, or microbial, and may be formulated for use in containers, ponds, drainage ditches, rice fields, or other standing water.

Chemical larvicides include organophosphates such as temephos, as well as insect growth regulators (IGRs) like methoprene and pyriproxyfen, which disrupt larval development. In some programs, formulations based on pyrethroids are used as larvicides, though their use may be limited by environmental concerns and resistance. Biological and microbial larvicides rely on living organisms or their products to target larvae. Examples include bacteria such as Bacillus thuringiensis israelensis (Bti) and Bacillus sphaericus (Bs), which produce toxins specific to dipteran larvae, as well as fungal agents like Metarhizium anisopliae and Beauveria bassiana and natural products such as spinosad.

Application of larvicides is typically part of integrated vector management, alongside source reduction, environmental management, and sometimes adulticiding. They are commonly used in areas where water bodies cannot be drained or treated by other means, and they may require repeated applications to maintain control depending on factors such as rainfall, water turnover, and larval turnover rates. Environmental and safety considerations include potential impacts on non-target organisms, water quality concerns, and regulatory approvals; Bti and Bs are generally regarded as having low non-target risk when used as directed. Resistance management practices, such as rotating active ingredients, are often recommended to sustain long-term effectiveness.