Electrophysiological investigation of larval water and potential oviposition chemo-attractants for Anopheles gambiae s.s.

Potential Anopheles gambiae s.s. breeding sites were sampled in rural sites in the Tanga region of Tanzania. Sites containing the largest numbers of An. gambiae larvae were small, shaded pools and rice fields. Water samples were collected from the larval sites and these, together with ether extracts of the water samples, were active in electro-antennogram (EAG) studies with female mosquitoes from a laboratory colony of Anopheles (Cellia) gambiae KWA. EAG response thresholds varied for 10 randomly selected water samples, from 0.01%-100% dilution for the whole water samples and from 0.001%-1.0% dilution for the ether extracts. Potential chemical components of the water samples were also electrophysiologically active with female An. gambiae antennae; thresholds varied from 1 ng (3-methylindole and indole) to 10 μg (m-cresol and 4-methylcyclohexanol).