Physical factors and chemical cues in the oviposition behavior of arboviral vectors Culex annulirostris and Culex molestus (Diptera: Culicidae)

Abstract

The role of physical factors (water depth and container color) and chemical cues (substances of mosquito origin and microbial mediated products) in attracting ovipositing adults of Culex annulirostris Skuse and Culex molestus Forskål were evaluated under laboratory conditions. Oviposition preference of Cx. annulirostris increased with the increase in water depth. For Cx. molestus , there was no significant difference in ovipositional preference between different water depths. Black and red were the most preferred colors for oviposition of Cx. annulirostris and Cx. molestus , respectively, whereas yellow and green were the least preferred colors for both species. For both Cx. annulirostris and Cx. molestus , fresh conspecific egg rafts with apical droplets did not act as an oviposition attractant. Cx. annulirostris preferred water containing conspecific larvae 6 times more often for oviposition than the control water. However, larvae of other species of mosquitoes— Cx. molestus and Aedes camptorhynchus (Thomson)—did not act as oviposition attractants. The oviposition preference of Cx. annulirostris for water containing conspecific larvae increased with the increase in larval density. Failure of antennectomized Cx. annulirostris females to discriminate between water containing conspecific larvae and water alone suggest the possible involvement of volatile olfactory stimuli in oviposition site selection. Cx. molestus preferred conspecific rearing water (water in which the mosquitoes completed development) for oviposition 7.6 times more than the control water. Preference for rearing water by Cx. molestus was caused by both visual and microbial mediated attractants. The bacterium Pseudomonas vesicularis (Dole and Freytag) isolated from the rearing water as well as from fermented food attracted the ovipositing Cx. molestus , confirming the role of bacteria as an oviposition attractant.