Longitudinal studies of Aedes aegypti (Diptera: Culicidae) in Thailand and Puerto Rico: blood feeding frequency

We used a histologic technique to study multiple blood feeding in a single gonotrophic cycle by engorged Aedes aegypti (L.) that were collected weekly for 2 yr from houses in a rural village in Thailand (n = 1,891) and a residential section of San Juan, Puerto Rico (n = 1,675). Overall, mosquitoes from Thailand contained significantly more multiple meals (n = 1,300, 42% double meals, 5% triple meals) than mosquitoes collected in Puerto Rico (n = 1,156, 32% double meals, 2% triple meals). The portion of specimens for which frequency of feeding could not be determined was 31% at both sites. We estimated that on average Ae. aegypti take 0.76 and 0.63 human blood meals per day in Thailand and Puerto Rico, respectively. However, frequency of multiple feeding varied among houses and, in Puerto Rico, the neighborhoods from which mosquitoes were collected. In Thailand 65% of the mosquitoes fed twice on the same day, whereas in Puerto Rico 57% took multiple meals separated by > or = 1 d. At both sites, the majority of engorged specimens were collected inside houses (Thailand 86%, Puerto Rico 95%). The number of blood meals detected was independent of where mosquitoes were collected (inside versus outside of the house) at both sites and the time of day collections were made in Puerto Rico. Feeding rates were slightly higher for mosquitoes collected in the afternoon in Thailand. Temperatures were significantly higher and mosquitoes significantly smaller in Thailand than in Puerto Rico. At both sites female size was negatively associated with temperature. Rates of multiple feeding were associated positively with temperature and negatively with mosquito size in Thailand, but not in Puerto Rico. Multiple feeding during a single gonotrophic cycle is a regular part of Ae. aegypti biology, can vary geographically and under different climate conditions, and may be associated with variation in patterns of dengue virus transmission.     

Effect of environmental temperature on the ability of Culex pipiens (Diptera: Culicidae) to transmit West Nile virus

Environmental temperature can affect the ability of mosquitoes to transmit an arbovirus. However, results of various studies indicate that these effects are not consistent among viruses or mosquito species, and there is no information available on the effect of environmental temperature on the ability of North American mosquito species to transmit West Nile (WN) virus. We evaluated the effect of incubation temperature (18, 20, 26, or 30 degrees C) on the ability of Culex pipiens L. derived from specimens collected during the outbreak in New York in 1999 to transmit a strain of WN virus obtained from a crow that died during this outbreak. Although mosquitoes fed on the same viremic chickens, infection rates were directly related to subsequent incubation temperatures. In mosquitoes held at 30 degrees C, virus was recovered from nearly all mosquitoes tested, disseminated infections were detected as early as 4 d after the infectious blood meal, and >90% of all mosquitoes had a disseminated infection 12 or more days after the infectious blood meal. In contrast, for mosquitoes held at 18 degrees C, disseminated infections were not detected until 25 d after the infectious blood meal, and even after 28 d, <30% contained a disseminated infection. Results for mosquitoes held at 20 and 26 degrees C were intermediate for both infection and dissemination rates. The effect of environmental temperature should to be considered when evaluating the vector competence of these mosquitoes and modeling risk of WN virus transmission in nature.     

Transmission studies of a European Sindbis virus in the floodwater mosquito Aedes vexans (Diptera: Culicidae)

Sindbis viruses are arthropod-borne viruses, which are maintained in nature in a Culex mosquitobird associated transmission cycle, but Aedes species have been suspected as playing a role in infecting humans. In this study, we addressed the question whether or not Germany's most abundant floodwater mosquito species Aedes vexans (Diptera, Culicidae) can serve as an efficient vector for Sindbis viruses. Firstly, the overall susceptibility of Ae. vexans was tested by intrathoracic inoculation of 40 plaque forming units (PFU) Karelian fever virus (KFV, an European Sindbis virus isolate) per female mosquito. Viral titres rose after inoculation reaching a maximum (about a 350-fold increase) between days 5 and 7. Throughout the three weeks of the experiment, virus was recovered from 85% of the individuals demonstrating that Ae. vexans became persistently infected with KFV. Oral infection studies were performed using KFV-spiked bovine blood and an artificial feeding device mimicking viremic animals with KFV titres between 3.7 × 10⁶ and 1.3 × 10⁷ PFU/ml. The bodies and legs of the mosquitoes were investigated separately. One week after oral infection, 1 out of 49, and another week later, none of the 36 mosquitoes harboured detectable virus. None of the legs yielded detectable virus at any point in time, indicating that no disseminated infection took place after oral uptake of the virus. Virus titres at 12 and 24 hours after the infectious blood meal were found to directly correspond to the amount of blood meal remaining in the midgut of engorged mosquitoes. Within 24 hours, 50% of the mosquitoes have apparently digested and excreted the blood and no virus could be re-isolated. Interestingly, virus could be recovered from the facces of these mosquitoes, collected from the bottom of the cage at 24 hours after feeding. In conclusion, the strain of German Ae. vexans used in this study was found to be refractory to KFV because of a midgut infection barrier. Thus, we assume that in a scenario in which Sindbis virus viremic birds travel through and roost in Germany during their migration, Ae. vexans would probably not play a role either as a bridge vector for human infections or in establishing a natural transmission cycle in Germany.     

Host feeding of mosquitoes (Diptera: Culicidae) associated with the recurrence of Rift Valley fever in Egypt

In 1993, Rift Valley fever (RVF) virus reappeared in Egypt. We determined the prevalence and feeding patterns of mosquitoes in 5 villages where the virus was active. Of 10 species recovered, Aedes caspius (Pallas), Culex pipiens L., Cx. antennatus (Becker), and Cx. perexiguus Theobald constituted 99% of > 35,000 mosquitoes captured in dry ice-baited CDC light traps. Ae. caspius was most prevalent, except at Nag' El Hagar where it was replaced by Cx. perexiguus. Cx. pipiens ranked 2nd, except at Nag' El Ghuneimiya, where it was replaced by Cx. antennatus. Most blood meals analyzed by an enzyme-linked immunosorbent assay reacted to > or = 1 antiserum. Cx. pipiens was mainly anthropophagic, and therefore may have been the main vector of RVF virus among humans. Ae. caspius feeds were chiefly from humans, bovines, and equines. Cx. antennatus and Cx. perexiguus fed generally on bovines. Mixed blood meals from humans and RVF virus susceptible animals were identified in the predominant mosquitoes. Prevalence and host selection, as well as predicted probability for a blood meal being interrupted, indicated that Ae. caspius may have served as a bridge vector between humans and bovines in 4 of the villages. Cx. perexiguus may have played this role at Nag' El Hagar. Because potential vectors are abundant, susceptible domestic animals are associated closely with humans, and surveillance of imported livestock is not systematic, we conclude that RVF virus sporadically will recur in Egypt.     

Laboratory and field evaluation of polymerase chain reaction-based forensic DNA profiling for use in identification of human blood meal sources of Aedes aegypti (Diptera: Culicidae)

We modified polymerase chain reaction (PCR)-based forensic DNA profiling for field studies on the feeding behavior of Aedes aegypti, the principal mosquito vector of dengue virus. Human DNA was extracted from oral swabs of human subjects and from blood-engorged mosquitoes, DNA was quantified by slot blot, and alleles at variable number tandem repeats and three short tandem repeats loci were amplified by PCR. Alleles were separated electrophoretically and then visualized by silver staining. A custom software program was written to match DNA fingerprints of potential human hosts to allelic profiles detected in engorged mosquitoes, and to calculate error rates for identification of human hosts of single and multiple-host blood meals. At 29 degrees C in the laboratory, human DNA recovered from mosquito blood meals declined an average of 67% 8 h after feeding and 90% after 24 h. We obtained complete allelic profiles from seven of 10 mosquitoes collected after 24 h. In a field trial, complete DNA profiles were obtained successfully for 43 people living in a rural village in south central Thailand and for 20 of 100 Ae. aegypti that contained blood and were collected in those peoples' homes. Blood imbibed from more than one person was detected in 45% (9 of 20) of the meals. Sixty-five percent of the meals contained blood from nonresidents of the house in which the mosquito was collected or from people who were not profiled; data consistent with the hypothesis that human movement is important for the spread of dengue virus within and among communities. When using alleles at four loci, all of the Thais and nine members spanning three generations of a Chinese-American family had unique allelic profiles. Error rates from classifying possible multiple-host meals as single-host meals were low (1-8%), with the highest error associated with closely related people. Results from our laboratory and field studies indicated that DNA profiling can be used to study the details and epidemiological implications of Ae. aegypti blood-feeding behavior.     

Vertical and venereal transmission of California group viruses by Aedes triseriatus and Culiseta inornata mosquitoes.

Aedes triseriatus and Culiseta inornata mosquitoes were compared in their ability to transmit vertically La Crosse (LAC) and snowshoe hare (SSH) viruses. LAC virus was transovarially transmitted by 53% of Ae. triseriatus, the natural vector, and by 22% of Cs. inornata mosquitoes. SSH virus was transovarially transmitted by 89% of Cs. inornata, a proposed natural vector, and by 29% of Ae. triseriatus. A genetic approach, using LAC, SSH, and LAC/SSH reassortant viruses was then used to elucidate viral genetic determinants of transovarial transmission of bunyaviruses by Ae. triseriatus mosquitoes. Viruses containing the LAC medium sized (M) RNA segment were most efficiently transovarially transmitted by Ae. triseriatus mosquitoes. LAC, SSH, and Tahyna (TAH) viruses were compared in their ability to be venerally transmitted. All three viruses replicated in the reproductive tract of male Aedes triseriatus and were venereally transmitted to female mosquitoes. LAC and TAH viruses infected previously blood fed (BF) but not non-blood fed (NBF) Aedes triseriatus female mosquitoes.     

Culex annulirostris (Diptera: Culicidae) host feeding patterns and Japanese encephalitis virus ecology in northern Australia

Japanese encephalitis virus (JEV) transmission in northern Australia has, in the past, been facilitated by Culex annulirostris Skuse feeding on domestic pigs, the primary amplifying hosts of the virus. To further characterize mosquito feeding behavior in northern Australia, 1,128 bloodmeals from Cx. annulirostris were analyzed using a double-antibody enzyme-linked immunosorbent assay. Overall, Cx. annulirostris obtained > 94% of blood meals from mammals, comprising marsupials (37%), pigs (20%), dogs (16%), and cows (11%), although the proportion feeding on each of these host types varied between study locations. Where JEV activity was detected, feeding rates on pigs were relatively high. At the location that yielded the first Australian mainland isolate of JEV from mosquitoes, feral pigs (in the absence of domestic pigs) accounted for 82% of bloodmeals identified, representing the first occasion that feeding on feral pigs has been associated with JEV transmission in Australia. Interestingly, < 3% of Cx. annulirostris had fed on pigs at locations on Badu Island where JEV was detected in multiple pools of mosquitoes in a concurrent study. This suggests that either alternative hosts, such as birds, which comprised 21% of blood meals identified, or infected mosquitoes immigrating from areas where domestic pigs are housed, may have contributed to transmission at this location. Because Cx. annulirostris is both an opportunistic feeder and the primary JEV vector in the region, environmental characteristics and host presence can determine JEV transmission dynamics in northern Australia.     

Impact of transmission cycles and vector competence on global expansion and emergence of arboviruses

Arboviruses are transmitted between arthropod vectors and vertebrate host. Arboviral infection in mosquitoes is initiated when a mosquito feeds on a viremic host. Following ingestion of a viremic blood meal by mosquitoes, virus enters midgut along with the blood, infects and replicates in midgut epithelial cells, and then escapes to the hemocoel, from where it disseminates to various secondary organs including salivary glands. Subsequently, when mosquito bites another host, a new transmission cycle is initiated. The midgut and salivary glands act as anatomical barriers to virus infection and escape. These complex interactions between the virus and vector dictate the vector competence. Thus, vector competence reflects the success in overcoming different barriers within the vector. Along with these, other intrinsic factors like midgut microbiota and immune responses, extrinsic factors like temperature and humidity, and genetic factors like vector genotype and viral genotype have been discussed in this review. Recent advancement on novel molecular tools to study vector competence is also included. Different modes of arboviral transmission like horizontal, vertical, and venereal and how these play role in sustenance and emergence of arboviruses in nature are also discussed. These factors can be exploited to reduce the susceptibility of vectors for the viruses, so as to control arboviral diseases to certain extent.     

Vector competence of Australian mosquitoes (Diptera: Culicidae) for Japanese encephalitis virus

Australian mosquitoes were evaluated for their ability to become infected with and transmit a Torres Strait strain of Japanese encephalitis virus. Mosquitoes, which were obtained from either laboratory colonies and collected using Centers for Disease Control and Prevention light traps baited with CO2 and octenol or reared from larvae, were infected by feeding on a blood/sucrose solution containing 10(4.5 +/- 0.1) porcine stable-equine kidney (PS-EK) tissue culture infectious dose50/mosquito of the TS3306 virus strain. After 14 d, infection and transmission rates of 100% and 81%, respectively, were obtained for a southeast Queensland strain of Culex annulirostris Skuse, and 93% and 61%, respectively, for a far north Queensland strain. After 13 or more days, infection and transmission rates of > 90% and > or = 50%, respectively, were obtained for southeast Queensland strains of Culex sitiens Wiedemann and Culex quinquefasciatus Say, and a far north Queensland strain of Culex gelidus Theobald. Although infection rates were > 55%, only 17% of Ochlerotatus vigilax (Skuse) and no Cx. quinquefasciatus, collected from far north Queensland, transmitted virus. North Queensland strains of Aedes aegypti L., Ochlerotatus kochi (D?nitz), and Verrallina funerea (Theobald) were relatively refractory to infection. Vertical transmission was not detected among 673 F1 progeny of Oc. vigilax. Results of the current vector competence study, coupled with high field isolation rates, host feeding patterns and widespread distribution, confirm the status of Cx. annulirostris as the major vector of Japanese encephalitis virus in northern Australia. The relative roles of other species in potential Japanese encephalitis virus transmission cycles in northern Australia are discussed.     

Importance of recrudescent avian infection in West Nile virus overwintering: incomplete antibody neutralization of virus allows infrequent vector infection

After the acute infection period, birds persistently infected with West Nile virus (family Flaviviridae, genus Flavivirus, WNV) occasionally shed virus into the bloodstream, but these virions normally are inactivated by neutralizing antibody. The current work tested the hypothesis that these host neutralizing antibodies protect mosquito vectors from WNV infection and reevaluated the minimum WNV infectious dose necessary to infect Culex tarsalis Coquillett. To determine whether host antibodies protect mosquitoes from infection, Cx. tarsalis and Culex stigmatosoma Dyar were fed bloodmeals containing avian blood, WNV, and sera with or without WNV-specific neutralizing antibodies. When viral particles were completely bound by antibody, mosquitoes were protected from infection; however, when incompletely bound, WNV titers as low as 10(2.3) plaque-forming units (pfu)/ml resulted in 5% infection. These data indicated that avian antibodies were protective to mosquito vectors and were not dissociated during digestion. Because recrudescent viremias may not attain the same magnitude as initial acute viremias, Cx. tarsalis vector competence was reevaluated focusing on the fate of low-titered bloodmeals. Females were evaluated for vector competence after ingesting bloodmeals containing 10(2.2), 10(3.4), 10(4.5), 10(5.5), or 10(6.5) WNV pfu/ml. Infection increased with bloodmeal titer, with 1% of the mosquitoes ingesting 10(3.4) pfu/ml and 45% of the mosquitoes ingesting 10(6.5) pfu/ml developing disseminated infections. The incomplete neutralization of recrudescent virus may be sufficient to infect a low proportion of competent blood-feeding Culex mosquitoes and perhaps allow persistently infected birds to provide a mechanism for arbovirus overwintering.     

Patterns of eastern equine encephalomyelitis virus infection in Culiseta melanura (Diptera: Culicidae)

Infection of the mosquito Culiseta melanura (Coquillett) by eastern equine encephalomyelitis virus was examined using transmission electron microscopy (TEM) of whole tagmata and fluorescent antibody assay (FA) and infectious assay (IA) of dissected tissues. Following infectious blood meals from chicks circulating different virus titers, mosquitoes were examined after extrinsic incubation intervals of 1-22 d. Virus was first detected by FA and IA in midguts and nonalimentary tissues 24 h after infection. Nascent virus was first visualized by TEM in several tissues, including midgut, fat body, and salivary glands, of high-titer-infected mosquitoes 48 h after they engorged. Moderate- and low-titer blood meals resulted in slightly slower appearance and dissemination of virus. Results were consistent with dissemination of virus from the posterior midgut to salivary glands via the hemolymph. Neural tissues contained little or no virus, whereas fat body appeared to be an important organ for virus replication and dissemination. Dissemination barriers did not accompany mosquito infections.     

Transmission of a newly recognized virus (Bunyaviridae, Bunyavirus) isolated from Aedes albopictus (Diptera: Culicidae) in Potosi, Missouri

Aedes albopictus (Skuse) mosquitoes collected in Potosi, Mo., were tested for their ability to transmit a newly recognized Bunyamwera sero group virus isolated from the same mosquito population. Mosquitoes were fed artificial blood meals containing 4.5-6.2 log10 TCID50 of virus per ml. After 7-29 d at 25 degrees C, 79-99% of the mosquitoes had disseminated infections and 0-26% transmitted virus to fluid-filled capillary tubes. Transmission was first observed after 7 d of extrinsic incubation. Tests failed to detect transovarial transmission in 5,145 progeny from ovarian cycles 2-4. Following parenteral inoculation with 5.3-6.0 log10 TCID50 of virus, four of nine adult hamsters developed viremia. Ten of 16 suckling mice died following intracerebral inoculation of 5.0 log10 TCID50 of virus (fifth Vero cell passage); the average survival time was 8.8 d (SD, 3.5). No mortality occurred in 10 suckling mice inoculated with 3.6 log10 TCID50 of virus (second Vero cell passage).     

Partitioning of glycogen, lipid, and sugar in ovaries and body remnants of female Aedes aegypti (Diptera: Culicidae) fed human blood

We examined the accumulation of glycogen, lipid, and sugar obtained from a human blood meal for egg development and body energy reserves by small and large female Aedes aegypti (L.). Small and large mosquitoes were fed a single meal of human blood on day 2 after emergence. Mosquitoes were collected at 4, 12, 24, 48, and 72 h after blood feeding and ovaries and body remnants were separated by dissection and then assayed. Large mosquitoes had greater reserves than small mosquitoes. Mosquitoes deposited similar proportions of lipid reserves obtained from blood meals in their ovaries regardless of body size. Small mosquitoes deposited a significantly higher proportion of their glycogen in ovaries than large mosquitoes. The pattern of energy accumulation and use indicates that to avoid starvation, mosquitoes fed a single human blood meal will need to feed again before ovipositing, and that multiple feeding may be more important for small than for large Ae. aegypti.     

Effect of triethylamine on the recovery of selected South American alphaviruses,flaviviruses, and bunyaviruses from mosquito (Diptera: Culicidae) pools

We evaluated the effect of triethylamine (TEA) on the recovery of infectious virus from pools of mosquitoes for two South American alphaviruses (eastern equine encephalomyelitis and Venezuelan equine encephalomyelitis subtypes IIIC and ID), one flavivirus (Ilheus) and two bunyaviruses (Mirim [Guama group] and Itaqui [group C]). Mosquitoes were inoculated intrathoracically with virus, held for 7-10 d at 26 degrees C, and handled under one of four regimens before testing for the presence of virus by plaque assay. Mosquitoes were killed by freezing at - 70 degrees C for 3 min and tested immediately for the presence of virus; killed by freezing at -70 degrees C for 3 min and then held at room temperature for 1 h before testing for the presence of virus; anesthetized with TEA and assayed immediately for the presence of virus; or anesthetized with TEA and then held at room temperature for 1 h before being assayed for the presence of virus. For each of the viruses tested, viral titers in mosquitoes anesthetized with TEA were similar to those in mosquitoes killed by freezing at-70 degrees C. Likewise, there was no significant difference in viral titers in mosquitoes anesthetized with TEA and held at room temperature for 1 h or in mosquitoes frozen at -70 degrees C and held at room temperature for 1 h before being processed for virus by isolation. Triethylamine is advantageous for the handling of mosquitoes in a field environment. The elimination of the need for a cold chain, without compromising virus recovery, increases the feasibility of conducting research projects requiring the isolation of live virus from mosquitoes in remote tropical environments.     

Why do female Aedes aegypti (Diptera: Culicidae) feed preferentially and frequently on human blood?

Adult female Aedes aegypti (L.), the vector of dengue and yellow fever viruses, have an affinity for feeding on human blood and a tendency to forego feeding on sugar. This observation challenges two tenets of mosquito biology: (1) mosquitoes imbibe plant carbohydrates for synthesis of energy reserves and blood for reproduction and (2) egg production is reduced when mosquitoes feed on human blood compared with blood from other species. Sub-optimal amounts of the amino acid isoleucine in human blood (particularly free isoleucine in plasma) are thought to be responsible for lowered egg production when human blood is ingested. We tested the hypothesis that feeding on human blood is associated with a selective advantage for Ae. aegypti and is an underlying reason for this mosquito's intimate and epidemiologically important relationship with human beings. Our five experiments examined the effects of different isoleucine concentrations on accumulated energy reserves, frequency of host contact, survival, and egg production. When mosquitoes imbibed blood meals over a 7- to 10-d period and were not fed sugar, increased isoleucine concentration decreased energy reserves and did not increase egg production. Aedes aegypti took smaller but more frequent blood meals when feeding on a low-isoleucine human host daily compared with a high-isoleucine mouse host. Previous reports that isoleucine enhances egg production were confirmed only when females were fed sugar, an unusual behavior for most domestic Ae. aegypti populations. Females fed human blood and water had greater age-specific survival (l(x)), reproductive output (m(x)), and cumulative net replacement (R0) than cohorts fed human blood plus sugar or isoleucine-rich mouse blood with or without access to sugar. The unique isoleucine concentration of human blood is associated with Ae. aegypti's unusual propensity to feed preferentially and frequently on humans--a behavior that increases this mosquito's fitness, synthesis of energy reserves, and contact with human hosts, making it an especially effective disseminator of human pathogens.     

Comparison of the transmission potential of two genetically distinct Sindbis viruses after oral infection of Aedes aegypti (Diptera: Culicidae)

Within mosquitoes, arboviruses encounter barriers to infection and dissemination that are critical determinants of vector competence. The molecular mechanisms responsible for these barriers have yet to be elucidated. The prototype Sindbis (SIN) strain, AR339, and viruses derived from this strain, such as TR339 virus, have limited infection and transmission potential in the medically important arthropod vector, Aedes aegypti (L.). However, the Malaysian SIN virus strain, MRE16, disseminates in nearly 100% of Ae. aegypti 14 d after oral infection. Here, we compare the spatial and temporal infection patterns of MRE16 and TR339 viruses in Ae. aegypti. The results indicate that a midgut escape barrier is primarily responsible for the significantly lower dissemination and transmission potentials observed after oral infection with TR339 virus. MRE16 and TR339 viruses now represent a well-characterized model system for the further study of virus determinants of vector infection, particularly determinants affecting the midgut escape barrier in Ae. aegypti.     

Host feeding pattern of Japanese encephalitis virus vector mosquitoes (Diptera: Culicidae) from Kuttanadu, Kerala, India

Identification of blood meals of vector mosquitoes is an important tool in the epidemiological investigations of vector-borne diseases. The blood meals of three mosquito species involved in the transmission of Japanese encephalitis virus (JEV) from the Kuttanadu area, Kerala, were determined using the agarose gel diffusion technique. A total of 4959 blood smears belonging to Culex (Culex) tritaeniorhynchus Giles (3273), Cx. (Culex) gelidus Theobald (64), Mansonia (Mnd.) indiana Edwards (735) ,and Ma. (Mnd.) uniformis (Theobald) (887) were tested. Cx. tritaeniorhynchus had predominantly fed on bovids (46.4%), and a good proportion (29%) had fed on more than one host. Cx. tritaeniorhynchus was highly zoophagic, and human feeding accounted for only 1.5% of those individuals successfully tested. Cx. gelidus showed bovid feeding at 36% and pig feeding at 12.5%. The test results showed 42.3% Ma. indiana and 12.2% Ma. uniformis had fed on humans. Multiple feeding was observed in Ma. indiana and Ma. uniformis, and most of the double feedings were from bovids and ovids (7.9 and 20.1%, respectively). Pig feeding accounted for 4.8% of the feedings by Cx. tritaeniorhynchus, 5.3% of Ma. indiana, and 6.4% of Ma. uniformis. This study is significant because of the role played by these mosquitoes in the transmission of JEV in the Kuttanadu area of Kerala, India.     

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.