Oviposition and Behavioral Responses of Culex quinquefasciatus to Skatole and Synthetic Oviposition Pheromone in Tanzania

Studies on the behavioral and oviposition responses of Culex quinquefasciatus to 3-methylindole or skatole (an oviposition site cue) and (5R,6S)-6-acetoxy-5-hexadecanolide (the synthetic oviposition pheromone, SOP) were conducted in Muheza, northeast Tanzania. Cx. quinquefasciatus displayed a bimodal pattern of oviposition. The highest peak (64.8%) was between 18:00 and 20:00 hr, while the second peak (18.9%) was between 06:00 and 08:00 hr. The mean number of egg rafts oviposited per day between the two peaks was different (P < 0.05). Oviposition responses of gravid Cx. quinquefasciatus differed across the range of concentrations of skatole. Larger numbers of egg rafts were deposited in bowls treated with 10^–6 g or 10^–5 g skatole than in bowls with tap water (P < 0.05). The number of egg rafts deposited in bowls treated with 10^–4 or 10^–1 g skatole was not different from that laid in tap water (P > 0.05). Under field conditions skatole was found to be effective for a period of seven days, after which its biological activity decreased significantly. It was further found that more egg rafts of Cx. quinquefasciatus were deposited in water treated with SOP than in water treated with skatole (P = 0.0002). An additive effect was observed when the SOP + skatole combination was used to attract gravid Cx. quinquefasciatus to oviposition sites. It is concluded that skatole and SOP mediate oviposition site selection of Cx. quinquefasciatus under field conditions.