Early Evening Questing and Oviposition Activity by the Culex (Diptera: Culicidae) Vectors of West Nile Virus in Northeastern North America

Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, MA 02115, USA.
Journal of Medical Entomology (Impact Factor: 1.95). 04/2007; 44(2):211-4. DOI: 10.1603/0022-2585(2007)44[211:EEQAOA]2.0.CO;2
Source: PubMed


To determine whether the Culex (Diptera: Culicidae) mosquitoes that transmit West Nile virus (family Flaviviridae, genus Flavivirus, WNV) in the northeastern United States seek hosts and oviposit contemporaneously, we recorded when these mosquitoes attacked caged birds and when they deposited eggs. They traversed oviposition sites most frequently approximately 2 h after astronomical sunset, and eggs generally were deposited at that time. Although they most frequently approached avian hosts approximately 2 h after sunset during midsummer, they are more opportunistic during mid- to late fall. Because the Culex mosquitoes that serve as the main vectors of West Nile virus in the northeastern United States quest for hosts and seek to oviposit well after sunset, insecticidal aerosols would be most effective when applied at that time.

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    • "The olfactometer was made of Perspex glass with internal diameter of 10 and 120 cm length from the release chamber to treatment/control chambers at the two arms. The experiment was done between 18:00 h and 20:00 h using a group of 20 gravid mosquitoes for each replicate because maximum nocturnal oviposition activity was observed in the first 2 h after the sunset and majority of the egg deposition occurred during the first 4 h (Reddy et al., 2007). In a dimly lit room, mosquitoes were aspirated and released in the releasing chamber of the olfactometer. "
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    ABSTRACT: Oviposition response of gravid Culex quinquefasciatus females to a series of synthetic fatty acid esters was evaluated at 10ppm under laboratory conditions. Octyl tridecanoate and propyl octadecanoate elicited respectively 85% and 73% increased ovipositional responses compared to control among the 16 esters tested. Other 14 esters showed highly significant repellency (67-96%) to gravid females. Standard 3-methyl indole received 69% increased egg deposition compared to control. In the Y-tube olfactometer, respectively 78, 64 & 58% orientation to octyl tridecanoate, propyl octadecanoate and 3-methyl indole was exhibited by the gravid C. quinquefasciatus females. Gravid females exhibited 19-41% reduced orientation toward treatment odors of other esters significantly different from respective control. Electroantennogram studies revealed 4-18 fold increased antennal response, in which 3-methyl indole, octyl tridecanoate and propyl octadecanoate elicited respectively 8, 18 and 15 fold EAG response compared to control. Relative EAG response of octyl tridecanoate compared to standard 3-methyl indole was significantly different. Reduced EAG responses were elicited by FAE-06, 08, 13, 14 & 15, while the relative EAG responses of other esters were at par with the standard stimulus. These, esters could be utilized potentially as oviposition attractants and repellents against C. quinquefasciatus females to reduce the breeding in polluted water along with existing integrated vector control methods.
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    • "Predictions for longer time scales (years or season to season) have indicated that suboptimal habitats may be chosen as the end of the suitable oviposition season is approached (Edgerly et al., 1998) and that timely rainfall can synchronize mosquito populations through oviposition (Shaman et al., 2002, 2005; Shaman & Day, 2007). For finely grained time scales, i.e. daily and hourly, it has been demonstrated that light plays a major role, inhibiting oviposition when continuous in laboratory settings (Suleman & Shirin, 1981) and delaying oviposition time in the field (Macdonald et al., 1981; Reddy et al., 2007). Similar inhibitory effects on oviposition at fine-grained temporal scales have been shown for strong winds and heavy rainfall (de Meillon et al., 1967). "
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    ABSTRACT: Oviposition is a major event in the life history of mosquitoes, shaping both individual fitness and vectorial capacity. Several exogenous factors have been shown as important for the dynamic forcing of oviposition at finely (hourly) and coarsely (monthly or season to season) grained temporal scales. However, field studies addressing the interplay of weather factors on oviposition dynamics at the intermediate (days to weeks) time scale are missing. Here, we present the results from a field study that showed the oviposition dynamics of the southern house mosquito, Culex quinquefasciatus Say (Diptera: Culicidae), to be: (i) primarily dictated by relative humidity; and (ii) disrupted by rainfall events that resulted in a modified sensitivity to relative humidity. Rainfall changed the concentration of ammonia, a major limiting resource of microbes used as food by mosquito larvae. Following major rainfall events, the importance of relative humidity in forcing the oviposition dynamics also changed. Finally, our results indicate that qualitative changes in oviposition habitats modify the importance of weather variables as predictors of mosquito oviposition dynamics.
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