A behavioural and electrophysiological study of oviposition cues for Culex quinquefasciatus

Both the synthetic oviposition pheromone. erythro-6-acetoxy-5-hexadecanolide (0.01-80 mug) and a polluted water sample (0.01-80%) significantly increased oviposition by gravid female Culex quinquefasciatus Say (Diptera: Culicidae) in a laboratory assay against clean water. An additive effect resulted when 0.05 mug oviposition pheromone was combined with the polluted water dilution series. Undiluted, however, both the oviposition pheromone and the polluted water sample, alone and in combination, reduced the oviposition response to control levels. A previously reported oviposition site odour component, 3-methylindole, also significantly increased oviposition at 1 x 10(-11) to 1 x 10(-8) g but at 1 X 10(-7) g significantly less oviposition occurred than in control treatments. The biological activities of the compounds were additionally evaluated electrophysiologically by an EAG assay. Female mosquitoes were electrophysiologically sensitive to the oviposition cues, both pheromone and habitat-related; EAG responses of males were considerably lower than of females with 3-methylindole.