Table 1 Summary of characteristics of compounds used as larvicides
Larvicides | Mode of action | Advantages | Limitations | Residual effect |
|---|---|---|---|---|
Bacterial larvicides | Induce the formation in larval midgut of a toxic pore that kill the mosquito by interrupting feeding and homeostasis | Harmless to most aquatic non-target organisms and humans, effective against insecticide resistant mosquitoes | Previous formulations had limited residual effect, require larvae to feed on, not active on late instar larvae and pupae | 2Â weeks previous formulations/up to 6Â months for new formulations |
Spinosyns | Toxic after ingestion and neurotoxic effect (bind to GABA and the nicotinic acetylcholine receptors and stop the normal transmission of nerve impulse and induce insect death). | Efficient against a large spectrum of species safe to non-target organisms, effective against insecticide resistant mosquitoes | Also used in agricultural, limited residual effect requiring frequent re-treatments | Short (1 to 3Â weeks) |
Petroleum products | Direct toxicity after ingestion or by contact reducing the mobility and prevent larvae from breathing causing suffocation and larval death | Control all mosquitoes, cheaper, easy to acquire, mosquito cannot develop resistance to the compound | Toxic to non-target species, frequent retreatment required, can be dispersed by wind, rain, vegetation or animals | Short (1 to 3Â week) |
Monomolecular surface films (MMF) | Prevent larvae from breathing and induce suffocation and larval death | Biodegradable, spread spontaneously over large water surface, safe to non-target organisms, mosquito cannot develop resistance to the compound | Can be dispersed by wind, rain, vegetation or animals | Short (up to 1Â week) |
Insect growth regulators | Prevent the development of larvae to adults or kill larvae when moulting | Efficient against several mosquito species, long residual effect, effective at low dosage, effective against insecticide resistant mosquitoes | Difficult to monitor if sites have been treated or not, toxic for non-target aquatic organisms | Long (3 to 6Â months) |
Essential oils and plant extracts | Toxic after ingestion or growth inhibiting effects | New compounds, could improve control of resistant mosquitoes | Not well characterised, no efficacy trial conducted, difficult to produce large quantities | Short |
Synthetic chemicals | Neurotoxic compounds which kill insects by blocking the normal transmission of nerve impulses | Easy to implement, effective in polluted habitats | Can select for insecticide resistance, harmful to non-target organisms, frequent re-treatment required, only organophosphates approved for larval control | Long (several weeks) |