Bird-baited traps for surveillance of West Nile mosquito vectors: effect of bird species, trap height, and mosquito escape rates

Host-seeking mosquitoes were sampled in bird-baited traps at four sites in New York state in 2003-2004. Trap placement and efficacy of chickens, Gallus gallus domesticus L., as bait compared with house sparrows, Passer domesticus L., an important reservoir of West Nile virus (family Flaviviridae, genus Flavivirus, WNV), was evaluated. Each site had a chicken-baited trap near ground level (approximately 1.5 m) and in the tree canopy (approximately 9 m), and a house sparrow-baited trap at ground level and canopy level. Each trap allowed mosquito access to birds on one end, and an inner mesh screen blocked bird access on the other end. The two most abundant mosquitoes, Culex restuans Theobald and Culex pipiens pipiens L., were differentiated using molecular characters. In 2003, Cx. restuans and Cx. p. pipiens made up 88% of total mosquito catch. In 2004, Cx. restuans comprised 43% of total catch and Cx. p. pipiens comprised 33%. The remaining species representing at least 1% of total catch were Ochlerotatus trivittatus (Coquillett), Coquilletidia perturbans (Walker), and Culiseta morsitans (Theobald). Capture rates were similar for chicken and house sparrow-baited traps; however, significantly more mosquitoes were captured in the canopy for both bird species. Cx. restuans preferred canopy traps, whereas equal numbers of Cx. p. pipiens were captured at ground and canopy levels. Mosquitoes were more likely to escape (74%) when excluded from birds than when allowed free access to birds (54%). Sentinel bird surveillance for WNV can be improved by trapping in the tree canopy in addition to ground level to capture the most important avian vectors.     

West Nile virus from female and male mosquitoes (Diptera: Culicidae) in subterranean, ground, and canopy habitats in Connecticut

In total, 93,532 female mosquitoes (Diptera: Culicidae) were captured in traps placed in subterranean (catch basin), ground (approximately 1.5 m above ground), and canopy (approximately 7.0 m above ground) habitats in Stamford and Stratford, CT, during 2003-2005. Culex pipiens L. was the most abundant (64.8%) of the 31 species identified. Significantly greater numbers of Cx. pipiens were captured in canopy-placed mosquito magnet experimental traps, and significantly greater numbers were collected in catch basin-placed (Centers for Disease Control) CDC traps than in CDC traps placed elsewhere. Culex restuans Theobald was captured in significantly greater numbers in traps placed in catch basins. Aedes vexans (Meigen), Aedes cinereus Meigen, and Aedes cantator (Coquillett) were significantly more abundant in ground traps. In total, 429 isolations of West Nile virus (WNV) were made from seven species of mosquitoes from late June through the end of October during 2003 through 2005. Three hundred ninety-eight (92.8%) isolates were from Cx. pipiens. Others were from Cx. restuans (n = 16), Culex salinarius Coquillett (n = 5), Ae. vexans (n = 4), Ae. cantator (n = 3), Aedes triseriatus (Say) (n = 2), and Ae. cinereus (n = 1). Multiple isolates from Cx. pipiens were made each week, primarily during the later part of July through the end of September. Weekly minimum infection rates (MIRs) were lower in 2004 (highest weekly MIR = 7.1) when no human cases were reported in Connecticut in comparison with 2003 and 2005 (highest weekly MIR = 83.9) when human cases were documented. Frequencies of infected pools were significantly higher in Cx. pipiens captured in traps in the canopy and significantly higher in catch basin placed traps than in traps at ground level. The physiological age structure of Cx. pipiens captured in the canopy was significantly different from that of Cx. pipiens collected in catch basins. Invariably, Cx. pipiens captured in the canopy were nulliparous or parous with ovaries in Christophers' stage 2, whereas 58.7% of the females captured in catch basins possessed ovaries filled with mature oocytes in Christophers' stage 5. Our results suggest that females in the canopy are seeking hosts, and after digestion of the bloodmeal and development of mature oocytes, they descend to catch basins for shelter and deposition of eggs. WNV was isolated from three, one, and two pools of male Cx. pipiens captured in catch basin-, ground-, and canopy-placed traps, respectively, and from six nulliparous Cx. pipiens females collected in the canopy. Weekly MIR ranged from 1.2 to 31.1 per 1,000 male specimens. These data show that mosquitoes become infected by means other than by blood feeding, possibly by transovarial transmission. The placement of traps in tree canopies and in catch basins can be used to augment current practices of placement of traps near the ground for surveillance of mosquitoes infected with WNV and for studies of the ecology of WNV.     

Attraction of Culex pipiens/restuans (Diptera: Culicidae) mosquitoes to bird uropygial gland odors at two elevations in the Niagara region of Ontario

In an effort to determine whether female Culex pipiens L. and Culex restuans Theobald mosquitoes (Diptera: Culicidae) are attracted to crow, Corvus brachyrhynchus, uropygial gland secretions, CDC miniature light traps (baited with CO2 but with the lights removed) were placed at approximately 1.5- and 5-m elevations, in 10 trees in awoodlot near Niagara Falls, Canada. These traps were assigned either a bird odor or a blank control. Bird odors were created by attaching cotton swabs coated with crow uropygial gland secretions to the trap intake. A significantly greater number of Cx. pipiens/ restuans were found in the 5-m traps compared with 1.5-m traps, with a significant number attracted to the bird odor over the no odor traps at the 5-m elevation, but not at 1.5 m. We also found more Aedes vexans (Meigen) in the 1.5-m traps than the 5-m traps; however, presence or absence of bird odor did not influence the distribution of Ae. vexans.     

Host-feeding habits of Culex and other mosquitoes (Diptera: Culicidae) in the Borough of Queens in New York City,with characters and techniques for identification of Culex mosquitoes

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.     

Host-seeking heights, host-seeking activity patterns, and West Nile virus infection rates for members of the Culex pipiens complex at different habitat types within the hybrid zone, Shelby County, TN, 2002 (Diptera: Culicidae)

Host-seeking heights, host-seeking activity patterns, and West Nile virus (family Flaviviridae, genus Flavivirus, WNV) infection rates were assessed for members of the Culex pipiens complex from July to December 2002, by using chicken-baited can traps (CT) at four ecologically different sites in Shelby County, TN. Host-seeking height was assessed by CT placed at elevations of 3.1, 4.6, and 7.6 m during one 24-h period per month. Host-seeking activity was assessed by paired CT placed at an elevation of 4.6 m. Can traps were sampled at one 10-h daytime interval and at seven 2-h intervals during the evening, night, and morning. Cx. pipiens complex mosquitoes accounted for 87.1% of collected mosquitoes. Culex (Melanoconion) erraticus (Dyar & Knab) accounted for 11.9% of specimens. The average number of Cx. pipiens complex mosquitoes collected per 24-h CT period from July to September was lowest at a rural middle income site (1.7), intermediate at an urban middle income site (11.3), and highest at an urban low income site (47.4). Can traps at the forested site failed to collect Cx. pipiens complex mosquitoes. From July to September at urban sites, Culex pipiens pipiens L. was the rarest of the three complex members accounting for 11.1-25.6% of specimens. At the rural site, Culex pipiens quinquefasciatus Say was the rarest member of the complex. Cx. p. pipiens was not collected after September. Mean abundance of Cx. pipiens complex mosquitoes was higher in traps at 7.6 m than in traps at 4.6 m. Abundances at 3.1 m were intermediate and not significantly different from abundances at the other heights. Initiation of host-seeking activity was associated with the end of civil twilight and activity occurred over an extended nighttime period lasting 8-10 h. All 11 WNV-positive mosquitoes were Cx. pipiens complex mosquitoes collected from urban sites in traps placed at elevations of 4.6 and 7.6 m. Infection rates were marginally nonsignificant by height. Infection rates, host-seeking heights, and activity patterns were not significantly different among members of the Cx. pipiens complex.     

Interspecific competition between larval Culex restuans Theobald and Culex pipiens L. (Diptera: Culicidae) in Michigan

Many invasive species succeed in becoming established in new locations because of their competitive superiority to native species. This has been shown in several examples involving mosquitoes. In this study, we examined the interspecific competition between mosquito larvae of a well-established, non-native species, Culex pipiens, and those of its ecologically similar, native congener Culex restuans. Small but significant differences in survival, growth, and development rates were found in Cx. restuans as a response to varying proportions of Cx. pipiens, suggesting that Cx. restuans is a slightly superior competitor. However, the overall differences between the species were small, and they may be nearly ecological equivalents as larvae. Nevertheless, the observed seasonal pattern of feeding and oviposition activity suggests some phenological avoidance of competition, thus demanding further study of the interaction of these two species.     

Culex pipiens (Diptera: Culicidae): a bridge vector of West Nile virus to humans

Host-feeding patterns of Culex pipiens L. collected in southwest suburban Chicago in 2005 were studied using polymerase chain reaction (PCR) and DNA sequencing techniques. Culex spp. mosquitoes, most identified to Cx. pipiens and the remainder to Cx. restuans by PCR, had fed on 18 avian species, most commonly American robin (Turdus migratorious), house sparrow (Passer domesticus), and mourning dove (Zenaida macroura). Additional blood meals were derived from four mammal species, primarily humans and raccoons (Procyon lotor). During a West Nile virus (WNV) epidemic in 2005, West Nile virus (WNV) RNA was detected in heads and thoraces of five Cx. pipiens (n = 335, 1.5%) using quantitative PCR. The hosts of these virus-infected, blood-fed mosquitoes included two American robins, one house sparrow, and one human. This is the first report of a WNV-infected Cx. pipiens mosquito collected during an epidemic of WNV that was found to have bitten a human. These results fulfill a criterion for incrimination of Cx. pipiens as a bridge vector.     

West Nile virus-infected dead corvids increase the risk of infection in Culex mosquitoes (Diptera: Culicidae) in domestic landscapes

A comparative study of West Nile virus (family Flaviviridae, genus Flavivirus, WNV) infection rates in Culex mosquitoes collected at 13 sites, seven reporting WNV-positive dead corvids (case sites) and six without reported dead birds (control sites) was conducted in Davis, CA, from 14 to 21 July at the beginning of the 2006 WNV outbreak. In total, 3051 Culex mosquitoes were collected using gravid traps and CO2-baited traps; WNV-infected mosquitoes were only collected with CO2-baited traps. WNV-infected Culex pipiens L. were collected at one of the seven case sites. Six of seven case sites yielded WNV-infected Culex tarsalis Coquillett, whereas only one of six control sites had WNV-infected Cx. tarsalis. Overall, the odds of finding WNV-positive mosquitoes were 19.75 times greater at sites reporting a WNV-infected dead corvid than sites without a WNV-infected dead corvid. Maximum likelihood estimates of the overall infection rates at the case sites were 3.48/1000 for Cx. tarsalis and 8.69/1000 for Cx. pipiens compared with 1.02/1000 in Cx. tarsalis collected at the control sites. Results indicate that Cx. tarsalis was important in early season enzootic transmission within Davis and that sites reporting WNV-infected dead corvids are areas to focus control and surveillance efforts.     

Mosquito abundance and bionomics in residential communities in Orange and Los Angeles Counties, California

Mosquito abundance and bionomics were studied intensively during summer and spring at two residential communities of contrasting economic status. Culex quinquefasciatus was the most abundant adult and immature mosquito collected in both communities, followed by Culiseta incidens, Culex stigmatosoma, and Culex tarsalis. Cx. stigmatosoma and Cx. tarsalis were more abundant in CO2 traps hung in tree canopy than at ground level and fed most frequently on birds. Cx. quinquefasciatus was abundant in both ground level and tree canopy CO2 traps and fed on both mammals and birds. Cs. incidens was collected most frequently by ground level CO2 traps and fed primarily on dogs. Cx. quinquefasciatus and Cs. incidens readily exploited peridomestic breeding sources, and resting adults were aggregated at houses with positive breeding sources. Although Cx. stigmatosoma and Cx. tarsalis larvae were collected primarily at peripheral breeding sources, the dispersion of resting adults was still clumped at houses within both communities. Mosquitoes were most abundant in the more affluent community due to an increased number of breeding sites created by automatic watering devices and poorly managed peripheral drainage channels. Resident opinion of recent mosquito annoyance was not related to the presence of mosquito breeding sources or the abundance of either resting or host-seeking mosquitoes.     

Oviposition activity patterns and West Nile virus infection rates for members of the Culex pipiens complex at different habitat types within the hybrid zone, Shelby County, TN, 2002 (Diptera: Culicidae)

Oviposition activity and West Nile virus (family Flaviviridae, genus Flavivirus, WNV) infection rates were assessed for members of the Culex pipiens complex from July through December 2002 by using gravid traps placed at four ecologically different sites in the southern portion of the hybrid zone in Shelby County, TN. Molecular assays identified three members of the Cx. pipiens complex: Cx. pipiens pipiens L., Cx. p. quinquefasciatus Say, and Cx. p. pipiens-Cx. p. quinquefasciatus hybrids (hybrids). The Cx. pipiens complex accounted for 90% of mosquitoes collected in gravid traps. All 285 WNV-positive mosquitoes were Culex mosquitoes, and 277 (97%) were Cx. pipiens complex mosquitoes. Infection rates among members of the Cx. pipiens complex were not significantly different. Infection rates were significantly higher at two urban sites than at a rural site, and WNV was not detected at a forested site. At urban sites, abundances of members of the Cx. pipiens complex corresponded to a simple latitude model of the hybrid zone. Cx. p. quinquefasciatus was most abundant (46.4%), followed by hybrids (34.1%) and Cx. p. pipiens (19.5%). The relative abundances at a rural site were reversed with Cx. p. pipiens (48.4%) being most abundant. This demonstrates that spatial habitat variation may profoundly influence the distribution of members of the Cx. pipiens complex within the hybrid zone. Members of the Cx. pipiens complex did not display different oviposition patterns. However, oviposition patterns assessed hourly at urban and rural sites were significantly different. At urban sites, oviposition activity of Cx. pipiens complex mosquitoes was bimodal with an evening peak associated with sunset and a morning peak associated with sunrise. At the rural site, the evening peak was pronounced and the morning peak weak and similar to nighttime activity.     

Sentinel pigeon surveillance for West Nile virus by using lard-can traps at differing elevations and canopy cover classes

Sentinel pigeons, Columba livia, were installed in lard-can traps at heights of 1.5 m and 7.6-9.1 m within differing canopy cover classes in New York City. Adult mosquitoes were collected weekly from July to October 2002, as were serum samples from each pigeon. Culex pipiens L. and Culex restuans Theobald comprised 97% of mosquitoes collected and were most numerous in canopy-level, forested traps. The West Nile virus (family Flaviviridae, genus Flavivirus, WNV) seroconversion rate was significantly greater for pigeons in canopy-level traps, although seroconversions occurred concurrently with human cases in the city and were of little prognostic value to public health agencies. Our results indicate that sentinel pigeons were most effective for monitoring enzootic transmission of WNV when placed in single-sentinel caging 7.6-9.1 m above ground level.     

Blood-feeding patterns of the Culex pipiens complex in Sacramento and Yolo Counties, California

Mosquitoes in the Culex pipiens complex are competent vectors of West Nile virus (WNV; family Flaviviridae, genus Flavivirus) in the laboratory, and field-collected mosquitoes have tested positive for the virus in California and elsewhere. A better understanding of Cx. pipiens complex blood-feeding patterns will help define the threat that these mosquitoes pose to human health and their role in WNV amplification in northern California. We collected blood-engorged Cx. pipiens complex mosquitoes from resting sites near and away from human habitation in Sacramento and Yolo Counties. Cytochrome c oxidase 1 gene sequences were used to identify the vertebrate species from which blood meals were taken. Of 330 engorged mosquitoes collected at 28 sites from June through August 2007 and May through August 2008, >99% fed on an avian host. Three mosquitoes contained bovine blood and none had fed on a human. American Robins (Turdus migratorius) were bitten most often, and the proportion of American Robin blood meals increased significantly over the summer. Other important avian hosts included House Finches (Carpodacus mexicanus), Barn Swallows (Hirundo rustica), Western Meadowlarks (Sturnella neglecta), and Mourning Doves (Zenaida macroura). In rural areas, Barn Swallows, Brewer's Blackbirds (Euphagus cyanocephalus), and House Sparrows (Passer domesticus) were frequent hosts. In settings near human habitation, Mourning Doves and Western Meadowlarks were common hosts. Our data indicate that in north central California mosquitoes in the Cx. pipiens complex may be more important as epiornitic than epidemic vectors of WNV.     

Hematophagous Diptera collected from a horse and paired carbon dioxide-baited suction trap in southern California: relevance to West Nile virus epizootiology

Hematophagous Diptera landing on a horse were removed by vacuum, and their numbers were related to a paired carbon dioxide-baited suction trap at three locations in southern California where West Nile virus activity was high during the preceding year. Insects collected from the horse included mosquitoes (nine species), biting midges (Culicoides sonorensis Wirth & Jones), and black flies (Simulium bivittatum Malloch). Mosquitoes were predominantly collected from the head, crest, withers, neck, chest, and shoulders of the horse, whereas biting midges and black flies were predominantly collected from the ventral midline of the horse. Culex erythrothorax Dyar was by far the most abundant mosquito species collected overall. Frequency of engorgement for mosquitoes captured from the horse ranged by species from zero to 58.3%, with Culex pipiens quinquefasciatus Say having the lowest value (16.7% or one of six mosquitoes) of species that fed on the horse. The number of insects captured at the horse and paired CO2-baited suction trap was not different for Anopheles franciscanus McCracken, Culex tarsalis Coquillett, and S. bivittatum. Cx. p. quinquefasciatus was captured in greater numbers in the CO2-baited suction trap, whereas Anopheles hermsi Barr & Guptavanji, Cx. erythrothorax, Culiseta inornata (Williston), and Culiseta particeps (Adams) were captured in greater numbers from the horse. The horse biting rate was very low for Cx. p. quinquefasciatus, intermediate for Cx. tarsalis, and very high for Cx. erythrothorax. Both Cx. tarsalis and Cx. erythrothorax should be considered likely epizootic vectors of West Nile virus to horses in rural southern California.     

Culex restuans (Diptera: Culicidae) relative abundance and vector competence for West Nile Virus

The abundance and vector competence of Culex restuans Theobald and Culex pipiens L. were compared to determine the relative importance of these species as West Nile virus (WNV) vectors in the northeastern United States. Abundance was estimated from egg raft collections at 12 sites in Albany, Suffolk, and Richmond counties, New York, during July, August, and September 2002 and 2003. Cx. restuans was more abundant than Cx. pipiens in both urban and rural areas, comprising 86% of 1,623 egg rafts collected. Vector competence for WNV was estimated after feeding on an artificial bloodmeal and in vitro transmission assays. The vector competence of the two species for WNV was similar, but the dynamics of infection seems to be mosquito species dependent. These findings suggest an important role for Cx. restuans in WNV transmission cycles in New York.     

Considerations for accurate identification of adult Culex restuans (Diptera: Culicidae) in field studies

Understanding the ecology and behavior of different mosquito species (Diptera: Culicidae) is essential for identifying their role in disease transmission cycles and public health risk. Two species of Culex mosquitoes in the northeastern United States, Culex pipiens L. and Culex restuans Theobald, have been implicated in enzootic transmission of West Nile virus (family Flaviviridae, genus Flavivirus, WNV). Despite the difficulty of differentiating these two species as adults, many public health workers and vector biologists collecting adults in the field separate these species based on external morphology. This approach is often used rather than examination of dissected male genitalia or polymerase chain reaction (PCR)-based diagnostics due to time or cost constraints. We evaluated the reliability of seven published morphological characters to differentiate adults of these species by comparing blindly scored morphology with PCR-based confirmations. Our study demonstrates that morphological identification of Cx. pipiens is marginal and often not reliable for Cx. restuans. We also examined error rates with molecular-based approaches. DNA samples were contaminated with as little as one leg from another species. We conclude that to fully understand the respective roles of Culex species in the epidemiology of WNV and other pathogens, more attention should be paid to these considerations for accurate species identification.     

Natural infection of Culex theileri (Diptera: Culicidae) with Dirofilaria immitis (Nematoda: Filarioidea) on Madeira Island, Portugal

Field and laboratory studies were performed to verify whether Culex theileri Theobald functions as a natural vector of Dirofilaria immitis (Leidy) on Madeira Island, Portugal. CO2-baited light traps (EVS traps) were use to sample mosquitoes monthly basis between February 2002 and February 2003 in the area of Quebradas (Funchal). Three mosquito species were captured, including 58 Culex pipiens L., 790 Cx. theileri, and three Culiseta longiareolata (Macquart). Only C. theileri tested positive for D. immitis. The presence of this filarial worm was detected by direct observation, infectivity assay dissection technique, and polymerase chain reaction methods. Infected mosquitoes were recovered in October and December 2002 and January 2003. These data provide evidence that Cx. theileri could be the main vector of D. immitis in Funchal, Madeira.     

Evaluation of four sampling techniques for surveillance of Culex quinquefasciatus (Diptera: Culicidae) and other mosquitoes in African rice agroecosystems

Field studies were conducted in a rice, Oryza sativa L., agroecosystem in Mwea Kenya to compare the efficiency of CO2-baited Centers for Disease Control (CDC) light traps against nonbaited CDC light traps and gravid traps against oviposition traps in outdoor collection of Culex quinquefasciatus Say (Diptera: Culicidae) and other mosquitoes. Collectively, 21 mosquito species from the genera Culex, Anopheles, Mansonia, Ficalbia, and Aedes were captured during the 10-wk study period. Cx. quinquefasciatus was the predominant species in all trap types with proportions ranging from 57% in the nonbaited CDC light traps to 95% in the gravid traps. Significantly higher numbers of Cx. quinquefasciatus and Culex annulioris Theobald were collected in the CO2-baited CDC light traps than in the nonbaited CDC light traps, but the numbers of other mosquito species, including malaria vectors Anopheles arabiensis Patton and Anopheles funestus Giles did not differ significantly between the two trap types. More Cx. quinquefasciatus females were collected in grass infusion-baited gravid traps than egg rafts of this species in oviposition traps containing the same infusion. Although most mosquitoes captured in CO,-baited and nonbaited CDC light traps were unfed, most of those collected in gravid traps were gravid. From these findings, it is concluded that at least in the rice-growing area of Mwea Kenya, CO2-baited CDC light traps in conjunction with gravid traps can be used in monitoring of Cx. quinquefasciatus both for control and disease surveillance.     

Cross-correlation map analyses show weather variation influences on mosquito abundance patterns in Saginaw County, Michigan, 1989-2005

Weather is important determinant of mosquito abundance that, in turn, influences vectorborne disease dynamics. In temperate regions, transmission generally is seasonal as mosquito abundance and behavior varies with temperature, precipitation, and other meteorological factors. We investigated how such factors affected species-specific mosquito abundance patterns in Saginaw County, MI, during a 17-yr period. Systematic sampling was undertaken at 22 trapping sites from May to September, during 1989-2005, for 19,228 trap-nights and 300,770 mosquitoes in total. Aedes vexans (Meigen), Culex pipiens L. and Culex restuans Theobald, the most abundant species, were analyzed. Weather data included local daily maximum temperature, minimum temperature, total precipitation, and average relative humidity. In addition to standard statistical methods, cross-correlation mapping was used to evaluate temporal associations with various lag periods between weather variables and species-specific mosquito abundances. Overall, the average number of mosquitoes was 4.90 per trap-night for Ae. vexans, 2.12 for Cx. pipiens, and 1.23 for Cx. restuans. Statistical analysis of the considerable temporal variability in species-specific abundances indicated that precipitation and relative humidity 1 wk prior were significantly positively associated with Ae. vexans, whereas elevated maximum temperature had a negative effect during summer. Cx. pipiens abundance was positively influenced by the preceding minimum temperature in the early season but negatively associated with precipitation during summer and with maximum temperature in July and August. Cx. restuans showed the least weather association, with only relative humidity 2-24 d prior being linked positively during late spring-early summer. The recently developed analytical method applied in this study could enhance our understanding of the influences of weather variability on mosquito population dynamics.     

Attractiveness of vertebrate hosts to Culex pipiens (Diptera: Culicidae) and other mosquitoes in Israel.

Host preferences of mosquitoes, mainly Culex pipiens L. and Aedes caspius (Pallas), were studied in Israel using live baits, chemical attractants, light, and suction traps. The feeding habits of Cx. pipiens were opportunistic. This species used a wide range of mammalian and avian hosts; a calf, chickens, turkeys, and sheep were the most attractive baits. A. caspius fed mainly on large mammals and was most attracted to calf and sheep baits. Although sheep were attractive, few Cx. pipiens and no Ae. caspius engorged after entering the traps. In addition to defensive behavior and the mechanical protection afforded by the wool, sheep may possess a close-acting repellent that deters mosquitoes from biting. CO2 was the best attractant for host-seeking Cx. pipiens and Ae. caspius, Aedes detritus (Haliday), Culiseta annulata (Schrank), Culiseta longiareolata (Macquart), and Uranotaenia unguiculata Edwards were caught in small numbers, and their bloodmeal hosts were recorded.