Oviposition and behavioral responses of Culex quinquefasciatus to skatole and synthetic oviposition pheromone in Tanzania

Studies on the behavioral and oviposition responses of Culex quinquefasciat us to 3-methylindole or skatole tan oviposition site cue) and (5R,6S)-6-ace toxy-5-hcxadecanolide (the synthetic oviposition pheromone, SOP) were condu cted in Muheza, northeast Tanzania. Cx. quinquefasciatus displayed a bimoda l 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 m ean number of egg rafts oviposited per day between the two peaks was differ ent (P < 0.05). Oviposition responses of gravid Cx. quinquefasciatus differ ed across the range of concentrations of skatole. Larger numbers of egg raf ts were deposited in bowls treated with 10(-6) mu g or 10(-5) pg skatole th an in bowls with tap water (P < 0.05). The number of egg rafts deposited in bowls treated with 10(-4) or 10(-1) mu g skatole was not different from th at laid in tap water (P > 0.05). Under field conditions skatole was found t o be effective for a period of seven days, after which its biological activ ity decreased significantly. It was further found that more egg rafts of Cx . quinquefasciatus were deposited in water treated with SOP than in water t reated 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 oviposit ion site selection of Cx quinquefasciatus under field conditions.