A field trial of the synthetic oviposition pheromone with Culex quinquefasciatus say (Diptera: Culicidae) in Kenya

Abstract

The synthetic attractant pheromone 6-acetoxy-5-hexadecanolide in a formulation of 20 mg containing 5 mg of the active (-)-(5i?,6S)-isomer in an effervescent tablet produced a high, positive overall response by gravid females of Culex quinquefasciatus Say when the mosquitoes were exposed to the pheromone in established breeding sites in western Kenya. Significantly more females (82%) oviposited around the pheromone source compared to a control. The activity of the pheromone persisted in the established breeding place for four days after application. The addition of the insect growth regulator S-31183 (2-[l-methyl-2-(4-phenoxyphenoxy)ethoxy]pyridine) to the formulation did not affect the activity of the pheromone. Newly-made breeding sites exposed domestically were not attractive initially for oviposition by gravid females but, after 18 days, they became more attractive. Trays treated with synthetic pheromone diverted females from similar unbaited trays exposed within 10 m. A sample of larvae taken from a site treated with pheromone and insect growth regulator showed 100% mortality by the pupal stage. Thus, the efficacy of the pheromone has been demonstrated for the first time in the field and the possibility of using this material in combination with a 'safe' insecticide confirmed.

Sampling GravidCulex quinquefasciatus(Diptera: Culicidae) in Tanzania with Traps Baited with Synthetic Oviposition Pheromone and Grass Infusions

“…quinquefasciatus deposited more egg rafts in grass infusion or pheromone than in tap water. Similar observations on the effect of pheromone have been reported by Otieno et al (1988). Strong attraction of Cx.…”

“…(5R,6S)-6-acetoxy-5-hexadecanolide (the synthetic oviposition pheromone, henceforth termed ÔpheromoneÕ) significantly affects oviposition site selection by this mosquito in East Africa (Otieno et al 1988. Recent studies in Muheza, Tanzania, also have indicated that volatiles from soakage pits and grass infusions attract Cx.…”

“…Oviposition attractants show great promise for surveillance (Reiter 1983, 1986) and, possibly, control (Otieno et al 1988) of Cx. quinquefasciatus.…”

“…Gravid females of Cx. quinquefasciatus are able to distinguish between sites with and without an oviposition pheromone at distances of up to 10 m (Otieno et al 1988). However, gravid females did not oviposit immediately in water carrying the pheromone alone in both Kenya (Otieno et al 1988) and Tanzania .…”

“…quinquefasciatus are able to distinguish between sites with and without an oviposition pheromone at distances of up to 10 m (Otieno et al 1988). However, gravid females did not oviposit immediately in water carrying the pheromone alone in both Kenya (Otieno et al 1988) and Tanzania . Although grass infusion-baited traps have proven their usefulness in sampling gravid Culex mosquitoes in the United States (Reiter 1983, Ritchie 1984, reports of sampling gravid mosquitoes in Africa are not available.…”