Using a proteomics approach, we identified 13 differentially abundant proteins in heads of nondiapause, early, and mid-diapause Culex pipiens L. adult females. Three proteins that were more abundant during early diapause showed highest identities to pupal cuticle protein (PCP). The majority of less abundant proteins were involved in energy metabolism and cytoskeletonal reorganization. The increase of PCP in early diapause may be involved in enhancing stress resistance in the cuticle, a response akin to the general enhancement of stress resistance associated with overwintering insects. PCP also may have utility as a biomarker for early diapause in this species.

The host-feeding patterns of mosquitoes (n = 247) collected in the Borough of Queens in New York City in July and August 2000 were investigated using an indirect ELISA and a polymerase chain reaction (PCR)-heteroduplex assay. Culex pipiens L. and Cx. restuans Theobald fed primarily on birds, and their feeding habits support their implication as enzootic vectors of West Nile virus. Culex salinarius Coquillett and Coquillettidia perturbans (Walker) fed mainly on mammals, with fewer blood meals taken from birds, and these two species are potential bridge vectors of West Nile virus. Culex mosquitoes took blood meals (n = 54) from 11 different avian species. Only the northern cardinal (Cardinalis cardinalis), American robin (Turdus migratorius), and Brown-headed cow bird (MolIothrus ater) were fed upon by all three Culex species. Multiple blood feedings on avian hosts were detected in Cx. pipiens and Cx. restuans. Species identifications of Culex mosquitoes made using morphological characteristics were confirmed with a PCR assay that employed species-specific primers. All Cx. pipiens (n = 20) and Cx. salinarius (n = 10) specimens were correctly identified, but three (20%) of 15 Cx. restuans were misidentified as Cx. pipiens.

In the northeast United States, control of West Nile virus (WNV) vectors has been unfocused because of a lack of accurate knowledge about the roles different mosquitoes play in WNV transmission. We analyzed the risk posed by 10 species of mosquitoes for transmitting WNV to humans by using a novel risk-assessment measure that combines information on the abundance, infection prevalence, vector competence, and biting behavior of vectors. This analysis suggests that 2 species (Culex pipiens L. and Cx. restuans Theobald [Diptera: Cilicidae]) not previously considered important in transmitting WNV to humans may be responsible for up to 80% of human WNV infections in this region. This finding suggests that control efforts should be focused on these species which may reduce effects on nontarget wetland organisms. Our risk measure has broad applicability to other regions and diseases and can be adapted for use as a predictive tool of future human WNV infections.

Wolbachia is a common maternally inherited bacterial symbiont able to induce crossing sterilities known as cytoplasmic incompatibility (CI) in insects. Wolbachia-modified sperm are unable to complete fertilization of uninfected ova, but a rescue function allows infected eggs to develop normally. By providing a reproductive advantage to infected females, Wolbachia can rapidly invade uninfected populations, and this could provide a mechanism for driving transgenes through pest populations. CI can also occur between Wolbachia-infected populations and is usually associated with the presence of different Wolbachia strains. In the Culex pipiens mosquito group (including the filariasis vector C. quinquefasciatus) a very unusual degree of complexity of Wolbachia-induced crossing-types has been reported, with partial or complete CI that can be unidirectional or bidirectional, yet no Wolbachia strain variation was found. Here we show variation between incompatible Culex strains in two Wolbachia ankyrin repeat-encoding genes associated with a prophage region, one of which is sex-specifically expressed in some strains, and also a direct effect of the host nuclear genome on CI rescue.

The urban area of Dakar, Senegal, contains > 5,000 market-garden wells that provide permanent sites for mosquito larvae, in particular Anopheles arabiensis Patton, the major vector of malaria. A study of the bioecology of mosquito larvae was conducted over 1 yr with a monthly visit to 48 of these wells. Overall, 9,589 larvae were collected of which 80.1% were Culicinae and 11.9% Anophelinae. Larvae from stages III and IV (n = 853) were identified to 10 species. An. arabiensis represented 86% of the anophelines collected and An. ziemanni Grunberg 14%. The most common Culicinae species included Aedeomyia africana Neveu-Lemaire, Culex quinquefasciatus Say, and Mimomyia splendens Theobald. Maximum anopheline abundance was observed at the end of the dry season in June, whereas maximum Culicinae abundance was observed at the end of the rainy season in September. Most wells (67%) did not harbor any An. arabiensis larvae and in the remaining 33% the larval abundance was low, averaging 0.54 larvae in stages III-IV per tray sample. To identify factors that determine the abundance of larvae in these wells, a co-inertia (multivariate) analysis was carried out to account for physicochemical variables (depth, turbidity, temperature, pH, conductivity, Na+, Cl-, HCO3-, CO3--, and NO3- concentrations) and biological variables (abundance of mosquito species, predators [e.g., fish, Dytiscidae, Notonectidae, odonates], molluscs [Bulinus and Biomphalaria], and surface plants [water lettuce, Lemna, and filamentous algae]). The co-inertia analysis indicated that the abundance of An. arabiensis was associated with Cx. quinquefasciatus and Cx. decens for the physiochemical data but was not associated with other mosquito species for floro-faunistic data. The conditions associated with abundant An. arabiensis were warm temperature (28-30 degrees C), clear and not too deep water (< 0.5 m), elevated concentrations of HCO3- and CO3--, low concentrations of NO3- and NaCl, low populations of larvivorous fish and invertebrate predators (notably odonates), the presence of water lettuce, and an absence of Lemna. These results indicate that many contributing factors influence the ecology of the immature stages of An. arabiensis.

Mosquitoes (Diptera: Culicidae) face their hosts' haemostatic mechanisms when attempting to feed on blood. Accordingly, they antagonize haemostasis by salivary agents that include anti-clotting, anti-platelet and vasodilatory compounds. Because haemostasis is a complex and redundant physiological response that varies between vertebrates, it is to be expected that haematophagous animals have a salivary armoury that most efficiently counteracts their preferred hosts. The mosquito Culex quinquefasciatus Say, which has a strong tendency to ornithophagy, appears to have only recently adapted to mammals and may not have evolved efficient mechanisms to counteract mammalian platelet responses, while birds only have relatively inefficient thrombocytes. Accordingly, we compared the probing behaviour of Cx. quinquefasciatus with two other mosquito species from different backgrounds: Aedes aegypti (L.) and Anopheles albimanus Weidemann, that have apparently had a longer evolutionary association with mammals. Culex takes much more time to find blood on a mammalian host (human or mouse) when compared to the two other mosquito species, but does not differ in probing behaviour when feeding on a chicken. Salivary anti-haemostatic components were also measured in those three species of mosquito and results are discussed in context with the probing behaviour.

A Hermes-based transposable element transformation system incorporating an enhanced green fluorescent protein (EGFP) marker was used to produce two transgenic lines of Culex quinquefasciatus (Say). The transformation frequency was approximately 12% and transformation of Culex was shown to be dependent on the presence of Hermes transposase. Injected Culex embryos were treated with four different heat shock regimes, two of which produced transformed individuals. These individuals were mated with wild-type mosquitoes and produced offspring which expressed the dominant EGFP gene in Mendelian ratios predicted for the stable integration of a gene at a single locus. The two transformed lines displayed distinct patterns of phenotypic expression, the expression of which has remained stable after fifteen generations. In these transgenic lines both the Hermes element and flanking plasmid DNA integrated into the Culex genome, as has been previously seen in Hermes-mediated transgenic strains of Aedes aegypti (L.). The high frequency of Culex transformation together with the dependence on the presence of Hermes transposase suggests that, as for Ae. aegypti, this mode of transposition into the germ-line genome occurs by an alternate mechanisms to the cut and paste type of transposition seen for this element in other insect species and in the somatic nuclei of mosquitoes. This is the first report of the genetic transformation of a species in the genus Culex and demonstrates that this medically important mosquito species can now, along with several other Culicine and Anopheline mosquito species, be genetically manipulated.

Mosquitoes were collected on human bait over a 16-month period (September 1988 to December 1989) in an urban and a rural area of Kinshasa, Zaïre. P. falciparum malaria sporozoite rates were determined by ELISA. In the urban area Culex quinquefasciatus accounts for 96% of the 121 bites/person/night (b/p/n). The only anopheline is Anopheles gambiae, sensu stricto, with an average of 5.1 b/p/n and a sporozoite rate of 1.86%. The entomological inoculation rate (EIR) averages 0.08 infective b/p/n. Malaria transmission is almost interrupted at the end of the dry season. In the rural area mosquito nuisance is small (20 b/p/n), almost entirely due to six species of Anopheles including four vectors of malaria: An.gambiae (13.3 b/p/n), An.funestus (2.4 b/p/n), An.nili (0.4 b/p/n) and An.brunnipes (0.7 b/p/n) with mean sporozoite rates of 7.85%, 6.60%, 6.63% and 0.53% respectively. An.paludis (0.4 b/p/n) and An.hancocki (0.2 b/p/n) were not found infective. Malaria transmission is intense and perennial: the overall EIR varies monthly between 0.60 and 3.29 infective b/p/n. The specific contributions of An.gambiae, An.funestus and An.nili average 1.07, 0.14 and 0.03 infective b/p/n respectively. Malaria transmission peaks during the rainy season in both study areas. The daily mean survival rates for An.gambiae were 0.91 and 0.78 in the rural and urban area, respectively. All An.gambiae examined belonged to the forest cytotype (Coluzzi et al., 1979). Through its effect on the sporozoite rate, the higher vector survival rate in the rural environment appears to be the major determinant of the greater malaria transmission rate in the rural area as compared to urban Kinshasa.

Insecticide resistance and absence of clinical cures or vaccines for many vector-borne diseases has stimulated interest in using genetically modified arthropod vectors for disease control. Current transgenic strategies focus on vector susceptibility to pathogen infection, which is an inefficient target for pathogen transmission interference. Manipulation of vector survival is theoretically more effective, resulting in larger reductions in the expected number of human infections. A hypothetical method to manipulate vector survival is to drive mortality-inducing Wolbachia into populations. For varying patterns and degrees of induced mortality, we outline the conditions under which virulent Wolbachia introductions into vector populations are expected to succeed and quantify the resultant reduction in pathogen transmission. The most critical component to the success of this strategy is the pattern of induced mortality. For operationally feasible introductions, induced mortality must be delayed until after vector reproduction begins. If this condition is not met, introduction thresholds become exceedingly high, ranging from approximately 40% to 90% of the total adult population. Delayed induced mortality patterns can reduce introduction thresholds to approximately 15-45% of the total adult population. Reduction in cytoplasmic incompatibility with male age has negligible effects on introduction success regardless of the induced mortality pattern. Under proper circumstances, symbiont-induced manipulation of vector survival can theoretically result in up to 100% reduction in pathogen transmission, depending on Wolbachia parameters, magnitude and pattern of induced mortality, and duration of pathogen incubation in the vector. Our results indicate that a broadening of the current paradigm for genetic manipulation of vectors to parameters other than arthropod vector competence is justified and will reveal new research possibilities for vector-borne disease control.