Larval Contact Assay: A Procedure to Evaluate Mosquito Larval Mortality following Direct Contact with Test Larvicidal Compound

To evaluate the potential of a test larvicidal compound, a dopamine receptor antagonist, using larval contact assay, begin with live mosquito larvae at their desired developmental or instar stage in aqueous media. Transfer equal numbers of the larvae to the wells of a multi-well plate.

Replace the media in the wells with deionized water to prevent any interference from contaminants that may negatively impact the larvae. Add increasing concentrations of the test compound to the respective wells.

Gently swirl the plate to facilitate contact between larvae and test compound. Incubate the plate under appropriate conditions.

Upon contact with the larvae, the test compound enters the body wall or outermost layer and reaches the spiracles, openings of the tracheal system, which are connected to the ganglia - cluster of nerve cells - comprising the central nervous system.

On the nerve cells, the test compound binds to the secondary binding sites of dopamine receptors, which are involved in critical cellular processes. This binding, even with neurotransmitter dopamine bound to the dopamine receptor, prevents receptor activation and downstream signaling, disrupting larval development, ultimately causing death. 

Record the number of non-responsive larvae, lacking movement, in each well at specific time point following test compound exposure across varying compound concentrations.

Increased larval mortality rate with increasing concentration indicates the larvicidal potential of the test compound.