Influence of Synthetic Oviposition Pheromone and Volatiles from Soakage Pits and Grass Infusions Upon Oviposition Site-Selection of Culex Mosquitoes in Tanzania

The response of Culex mosquitoes to (5R,6S)-6-acetoxy-5-hexadecanolide (the synthetic oviposition pheromone, SOP), emanations from soakage pit water (SPW), and grass infusions (GI) was studied in pit latrines in Muheza, Tanzania. Water treated with the synthetic oviposition pheromone received more egg rafts of Culex quinquefasciatus Say and Cx. cinereus Theobald than did the untreated water (P < 0.001). The residual activity of SOP did not decrease over a nine-day period, with the geometric mean number of egg rafts laid in the SOP-treated water varying daily between 2.5 and 8.9 as compared to 0.1–1.6 egg rafts laid in tap water. However, SOP did not attract ovipositing mosquitoes to nonbreeding sites, and both treatment and control received few eggs. SPW and GI attracted ovipositing Cx. quinquefasciatus, Cx. cinereus, and Cx. tigripes Grandpré and de Charmoy with the number of eggs rafts deposited in bowls containing SPW or GI being larger than that deposited in bowls with tap water (P < 0.05). More egg rafts of Cx. quinquefasciatus were deposited in SOP-treated water than in SPW (P < 0.05). When SOP was compared with SOP + SPW, more egg rafts of Cx. quinquefasciatus were deposited in bowls with the latter combination than in bowls containing SOP or SPW only (P < 0.05), indicating a synergistic effect between SOP and SPW. Similarly, when SOP-treated water and GI were compared with SOP + GI, more egg rafts of Cx. quinquefasciatus were laid in the latter bowl, indicating a synergistic effect between SOP and GI. The result suggest that the combined use of SOP and organically enriched water can be employed in monitoring of Cx. quinquefasciatus for control programs. This is the first record of the attraction of Cx. cinereus and Cx. tigripes to oviposition stimuli.