Infectivity and pathogenicity of a novel baculovirus, CuniNPV from Culex nigripalpus (Diptera: Culicidae) for thirteen species and four genera of mosquitoes

The infectivity and pathogenicity of newly discovered baculovirus, CuniNPV (family Baculoviridae, genus Nucleopolyhedrovirus) originally isolated from the mosquito Culex nigripalpus Theobald, was evaluated in laboratory bioassys against thirteen species and four genera of mosquitoes native to the northeastern U.S. Purified virus at a dosage rate of 1.6 x 10(7) occlusion bodies/ml with 10 mM Mg2+ added was used in exposures with second through fourth instars at temperatures ranging from 17 to 27 degrees C. High infection rates and accompanying mortality were achieved in Cx. pipiens L. (83.0-14.4%), Cx. pipiens f. molestus (80.4% infection), and Cx. salinarius Coquillett (48.0-43.1%). Cx. restuans Theobald was also susceptible but infection rates were lower (21.3-12.5%). The gross pathology associated with infection was identical to that reported in Cx. nigripalpus. Infected larvae were lethargic and were often suspended at the water surface. Development of CuniNPV was observed in the nuclei of the midgut epitheial cells in the gastric caeca and posterior region of the stomach of host larvae. One hundred percent mortality was observed in all larvae that exhibited gross symptoms of infection within 4-d p.i. Cx. territans Walker (subgenus Neoculex Dyar) was the only Culex mosquito that was not susceptible. No infections were obtained with any species of Aedes [Ae. vexans (Meigen)], Culiseta [Culiseta morsitans (Theobald)] or Ochlerotatus [Ochlerotatus canadensis (Theobald), Oc. cantator (Coquillett), Oc. communis (De Geer), Oc. excrucians (Walker), Oc. japonicus (Theobald), Ochlerotatus stimulans (Walker), and Ochlerotatus triseriatus (Coquillett)]. The host range of CuniNPV appears to be restricted to Culex mosquitoes within the subgenus Culex. An inhibitory effect on transmission of CuniNPV was observed when a liver powder/Brewer's yeast mixture was used as a source of food reinforcing the critical role of Mg2+ and sensitivity of the infection process to the presence other divalent cations (Cu2+, Fe2+, and Zn2+) in the larval medium that interfered with the infection process. The high infectivity and pathogenicity of CuniNPV for the principal vectors of West Nile virus in North America make CuniNPV an attractive candidate for future development as a biopesticide.     

Potential for North American mosquitoes (Diptera: Culicidae) to transmit rift valley fever virus

To determine which arthropods should be targeted for control should Rift Valley fever virus (RVFV) be detected in North America, we evaluated Culex erraticus (Dyar and Knab), Culex erythrothorax Dyar, Culex nigripalpus Theobald, Culex pipiens L., Culex quinquefasciatus Say, Culex tarsalis Coquillett, Aedes dorsalis (Wiedemann), Aedes vexans (Meigen), Anopheles quadrimaculatus Say, and Culicoides sonorensis Wirth and Jones from the western, midwestern, and southern United States for their ability to transmit RVFV. Female mosquitoes were allowed to feed on adult hamsters inoculated with RVFV, after which engorged mosquitoes were incubated for 7-21 d at 260C, then allowed to refeed on susceptible hamsters, and tested to determine infection, dissemination, and transmission rates. Other specimens were inoculated intrathoracically, held for 7 d, and then allowed to feed on a susceptible hamster to check for a salivary gland barrier. When exposed to hamsters with viremias > or =10(8.8) plaque-forming units/ml blood, Cx. tarsalis transmitted RVFV efficiently (infection rate = 93%, dissemination rate = 56%, and estimated transmission rate = 52%). In contrast, when exposed to the same virus dose, none of the other species tested transmitted RVFV efficiently. Estimated transmission rates for Cx. erythrothorax, Cx. pipiens, Cx. erraticus, and Ae. dorsalis were 10, 8, 4, and 2%, respectively, and for the remaining species were < or = 1%. With the exception of Cx. tarsalis and Cx. pipiens, all species tested had moderate to major salivary gland barriers. None of the C. sonorensis became infected and none of the An. quadrimaculatus tested transmitted RVFV by bite, even after intrathoracic inoculation, indicating that these species would not be competent vectors of RVFV. Although Ae. vexans from Florida and Louisiana were relatively efficient vectors of RVFV, specimens of this species captured in Colorado or California were virtually incompetent, illustrating the need to evaluate local population for their ability to transmit a pathogen. In addition to laboratory vector competence, factors such as seasonal density, host feeding preference, longevity, and foraging behavior should be considered when determining the potential role that these species could play in RVFV transmission.     

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.     

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.     

Weather and land cover influences on mosquito populations in Sioux Falls, South Dakota

This study compared the spatial and temporal patterns of Culex tarsalis Coquillett and Aedes vexans Meigen populations and examined their relationships with land cover types and climatic variability in Sioux Falls, SD. Between 24 and 30 CDC CO2-baited light traps were set annually in Sioux Falls from May to September 2005-2008. Land cover data were acquired from the 2001 National Land Cover Dataset and the percentages of selected land cover types were calculated within a 600-m buffer zone around each trap. Meteorological information was summarized from local weather stations. Cx. tarsalis exhibited stronger spatial autocorrelation than Ae. vexans. Land cover analysis indicated that Cx. tarsalis was positively correlated with grass/hay, and Ae. vexans was positively correlated with wetlands. No associations were identified between irrigation and the host-seeking population of each species. Higher temperature in the current week and 2 wk prior and higher precipitation 3-4 wk before collection of host-seeking adult mosquitoes had positive influences on Cx. tarsalis abundance. Temperature in the current week and rainfall 2-3 wk before sampling had positive influences on Ae. vexans abundance. This study revealed the different influences of weather and land cover on important mosquito species in the Northern Great Plains region, which can be used to improve local vector control strategies and West Nile virus prevention efforts.     

Vector competence of Mexican and Honduran mosquitoes (Diptera: Culicidae) for enzootic (IE) and epizootic (IC) strains of Venezuelan equine encephalomyelitis virus

Experimental studies evaluated the vector competence of Ochlerotatus taeniorhynchus (Wiedemann), Culex cancer Theobald, Culex pseudes (Dyar and Knab), Culex taeniopus Dyar and Knab, and a Culex (Culex) species, probably Culex quinquefasciatus Say, and Culex nigripalpus Theobald from Chiapas, Mexico, and Tocoa, Honduras, for epizootic (IC) and enzootic (IE) strains of Venezuelan equine encephalomyelitis (VEE) virus. Culex pseudes was highly susceptible to infection with both the IC and IE strains of VEE (infection rates >78%). Patterns of susceptibility to VEE were similar for Oc. taeniorhynchus collected in Mexico and Honduras. Although Oc. taeniorhynchus was highly susceptible to the epizootic IC strains (infection rates > or = 95%, n = 190), this species was less susceptible to the enzootic IE strain (infection rates < or = 35%, n = 233). The Culex (Culex) species were refractory to both subtypes of VEE, and none of 166 contained evidence of a disseminated infection. Virus-exposed Cx. pseudes that refed on susceptible hamsters readily transmitted virus, confirming that this species was an efficient vector of VEE. Although Oc. taeniorhynchus that fed on hamsters infected with the epizootic IC strain transmitted VEE efficiently, only one of six of those with a disseminated infection with the enzootic IE virus that fed on hamsters transmitted virus by bite. These data indicate that Cx. pseudes is an efficient laboratory vector of both epizootic and enzootic strains of VEE and that Oc. taeniorhynchus could be an important vector of epizootic subtypes of VEE.     

Host-feeding patterns of Culex pipiens and other potential mosquito vectors (Diptera: Culicidae) of West Nile virus (Flaviviridae) collected in Portugal

The host blood-feeding patterns of mosquito vectors affects the likelihood of human exposure to zoonotic pathogens, including West Nile Virus (family Flaviviridae, genus Flavivirus, WNV). In Portugal, data are unavailable regarding the blood-feeding habits of common mosquito species, including Culex pipiens L., considered the primary vector of WNV to humans. The sources of bloodmeals in 203 blood-fed mosquitoes of nine species collected from June 2007 to November 2010 in 34 Portuguese counties were analyzed by sequencing cytochrome-b partial fragments. Cx. pipiens was the most common species collected and successfully analyzed (n = 135/78). In addition, blood-fed females of the following species were analyzed: Ochlerotatus caspius Pallas (n = 20), Culex theileri Theobald (n = 16), Anopheles maculipennis s.l. Meigen (n = 10), Culiseta longiareolata Macquart (n = 7), Aedes aegypti L. (n = 6), Culex perexiguus Theobald (n = 3), Culiseta annulata Schrank (n = 3), and Ochlerotatus detritus Haliday (n = 3). The Cx. pipiens mosquitoes fed predominantly on birds (n = 55/78, 70.5%), with a high diversity of avian species used as hosts, although human blood was identified in 18 specimens (18/78, 23.1%). No significant differences were found between the host-feeding patterns of blood-fed Cx. pipiens collected in residential and nonresidential habitats. The occurrence of human derived blood meals and the presence of a mix avian-human bloodmeal accordingly suggest this species as a potential vector of WNV. Therefore, in Portugal, Cx. pipiens may play a role both in the avian-to-avian enzootic WNV cycle and in the avian-to-mammal transmission. In this context, the identity of Cx. pipiens (considering the forms molestus and pipiens) and the potential consequence on feeding behavior and WNV transmission are discussed.     

Mosquito bionomics and the lack of arbovirus activity in the Chino area of San Bernardino County, California

Mosquito bionomics, including temporal abundance, metabolic status, and blood-feeding patterns, and arbovirus activity were studied at representative dairy and residential habitats in Chino, Calif., during 1987 and 1988. Host-seeking Culex tarsalis Coquillett and Cx. quinquefasciatus Say females were more abundant and appeared earlier each season at traps near dairy breeding sources than at traps in residential areas, whereas Cx. stigmatosoma Dyar, which also breeds in dairy effluent, was most abundant at residential traps. All three Culex species remained gonotrophically active throughout winter and did not appear to enter diapause. Dairy cows diverted the normally ornithophagic Cx. tarsalis and Cx. quinquefasciatus females from avian hosts in dairy, but not in residential, habitats. Cx. stigmatosoma fed almost exclusively on birds. The diversion of host-seeking Cx. tarsalis females to bovine hosts and reduced abundance because of mosquito abatement may have combined to reduce the receptivity of the Chino area to St. Louis encephalitis virus.     

Ochlerotatus taeniorhynchus: a probable vector of Dirofilaria immitis in coastal areas of Yucatan, Mexico

Mosquito collections were done on microfilaremic dogs, positive for Dirofilaria immitis (Leidy), for 15 consecutive nights in Celestun, Yucatan, southeastern Mexico, during January 2007. In total, 275 mosquitoes (3 male and 272 female) of five species were collected: Ochlerotatus taeniorhynchus (Wiedemann), Ochlerotatus sollicitans (Walker), Culex quinquefasciatus Say, Culex interrogator (Dyar & Knab), and Aedes aegypti (L.). Oc. taeniorhynchus was the species most frequently collected, and it had the highest rate of feeding success and the highest attack rates. First (L1) and third (L3) instars of Dirofilaria were observed in all mosquito species collected except for Ae. aegypti: 23 of 223 Oc. taeniorhynchus, three of 40 Cx. quinquefasciatus, and one of six Oc. sollicitans and one of one Cx. interrogator were infected with Dirofilaria (10.3% of total examined mosquitoes). This is the first report of Dirofilaria (presumably D. immitis) isolation from wild-caught mosquitoes in Mexico. Results imply that D. immitis can develop from microfilaria to infective L3s in Oc. taeniorhynchus, Cx. quinquefasciatus, and Oc. sollicitans, but L3s (infectious) were only recovered in heads of Oc. taeniorhynchus. Thus, Oc. taeniorhynchus can be considered a potential vector of dirofilariasis in Celestun, because infective L3 Dirofilaria were found in the vicinity of the mouthparts, and this mosquito has a strong association with microfilaremic dogs in this study area.     

Effect of the anesthetizing agent triethylamine on western equine encephalomyelitis and St. Louis encephalitis viral titers in mosquitoes (Diptera: Culicidae)

Triethylamine (TEA) is a chemical compound that provides an effective means to anesthetize mosquitoes. The mosquitoes remain alive but are incapacitated for several hours; they do not recover following treatment. There was no effect on the titers of infectious virus recovered from western equine encephalomyelitis or St. Louis encephalitis virus-infected Culex tarsalis Coquillett and Aedes dorsalis (Meigen) that were anesthetized with TEA prior to storage at -70 degrees C. Furthermore, TEA had no effect on isoenzyme profiles of uninfected Cx. tarsalis.     

Mosquito abundance is correlated with cliff swallow (Petrochelidon pyrrhonota) colony size

We measured the abundance of mosquitoes [primarily Aedes vexans (Meigen) and Culex tarsalis Coquillett] at cliff swallow (Petrochelidon pyrrhonota Vieillot) colonies of different sizes in southwestern Nebraska in 1999. Using CO2 traps placed inside and outside of colonies, we found that total mosquito abundance increased significantly with the number of active cliff swallow nests at a colony site. We found no effect of date or weather conditions on the number of mosquitoes caught it the different sites. By classifying the landscape from aerial photographs within a 2-km-diameter circle centered on each colony site, we found no significant relationships between habitat type near a colony site and cliff swallow colony size or mosquito abundance. Proximity to livestock could not account for our results. Culex tarsalis was proportionately more likely to be caught inside a colony than at traps 30 in away, but the proportion of C. tarsalis inside a colony did not vary with colony size. Our results cannot be explained by date- or weather-related sampling artifacts or by differences in habitat between sites. Most likely, mosquitoes, especially A. vexans, are attracted to the vicinity of large cliff swallow colonies.     

Comparative analysis of distribution and abundance of West Nile and eastern equine encephalomyelitis virus vectors in Suffolk County, New York, using human population density and land use/cover data

Five years of CDC light trap data from Suffolk County, NY, were analyzed to compare the applicability of human population density (HPD) and land use/cover (LUC) classification systems to describe mosquito abundance and to determine whether certain mosquito species of medical importance tend to be more common in urban (defined by HPD) or residential (defined by LUC) areas. Eleven study sites were categorized as urban or rural using U.S. Census Bureau data and by LUC types using geographic information systems (GISs). Abundance and percent composition of nine mosquito taxa, all known or potential vectors of arboviruses, were analyzed to determine spatial patterns. By HPD definitions, three mosquito species, Aedes canadensis (Theobald), Coquillettidia perturbans (Walker), and Culiseta melanura (Coquillett), differed significantly between habitat types, with higher abundance and percent composition in rural areas. Abundance and percent composition of these three species also increased with freshwater wetland, natural vegetation areas, or a combination when using LUC definitions. Additionally, two species, Ae. canadensis and Cs. melanura, were negatively affected by increased residential area. One species, Aedes vexans (Meigen), had higher percent composition in urban areas. Two medically important taxa, Culex spp. and Aedes triseriatus (Say), were proportionally more prevalent in residential areas by LUC classification, as was Aedes trivittatus (Coquillett). Although HPD classification was readily available and had some predictive value, LUC classification resulted in higher spatial resolution and better ability to develop location specific predictive models.     

Molecular phylogeny and evolutionary relationships among mosquitoes (Diptera: Culicidae) from the northeastern United States based on small subunit ribosomal DNA (18S rDNA) sequences

The phylogenetic relationships of Culicidae native to the northeastern United States were investigated by analyzing small subunit ribosomal DNA (18S rDNA) sequences obtained from 39 species representing nine genera. Molecular phylogenies were consistent with traditional classifications based on morphological characters except for the placements of Psorophora Robineau-Desvoidy and Uranotaenia Lynch Arribalzaga. In our analyses, 1) Anopheles Meigen was strongly supported as the sister taxon to the remaining Culicidae; 2) Toxorhynchites Theobald was represented as a distinct monophyletic sister group to the Culicinae; 3) Psorophora formed a basal clade to Culiseta Felt, Coquillettidia Dyar, and Culex L. but also was shown as a sister taxon to Aedes Meigen and Ochlerotatus Lynch Arribalzaga; 4) Coquillettidia perturbans (Walker) seems to be a sister group to Culiseta; 5) placement of Uranotaenia was inconclusive and seemed to be either a sister group to the Aedes and Ochlerotatus or a basal taxon to all other culicines; and 6) Aedes and Ochlerotatus formed two separate and distinct clades, providing phylogenetic data consistent with the recent elevation of Ochlerotatus to the generic level as proposed by Reinert (2000). The utility of 18S rDNA for evaluating phylogenetic and evolutionary relationships among mosquito taxa was demonstrated at the genus and species levels. To our knowledge, this study represents the first molecular-based phylogenetic study of mosquito species occurring within this geographic region of North America and contains the largest number of species that have been examined among the genera Aedes and Ochlerotatus.     

Experimental transmission of eastern equine encephalitis virus by Ochlerotatus j. japonicus (Diptera: Culicidae)

We evaluated the potential for Ochlerotatus j. japonicus (Theobald), a newly recognized invasive mosquito species in the United States, to transmit eastern equine encephalitis (EEE) virus. Aedes albopictus (Skuse) and Culex pipiens (L.) were similarly tested for comparison. Ochlerotatus j. japonicus and Ae. albopictus became infected and transmitted EEE virus by bite after feeding on young chickens 1 d after they had been inoculated with EEE virus (viremias ranging from 10(7.0-8.7) plaque-forming units [PFU]/ml of blood). No Cx. pipiens (n = 20) had detectable levels of virus 14 d after feeding on an EEE-virus infected chicken with a viremia of 10(8.1) PFU per ml of blood. Depending on the viral titer in the donor chicken, infection rates ranged from 55-100% for Oc. j. japonicus and 93-100% for Ae. albopictus. In these two species, dissemination rates were identical to or nearly identical to infection rates. Depending on the viral titer in the blood meal, estimated transmission rates ranged from 15 to 25% for Oc. j. japonicus and 59-63% for Ae. albopictus. Studies of replication of EEE virus in Oc. j. japonicus showed that there was an "eclipse phase" in the first 4 d after an infectious blood meal, that viral titers peak by day 7 at around 10(5.7) per mosquito, and that virus escaped the mid-gut as soon as 3 d after the infectious blood meal. These data, combined with the opportunistic feeding behavior of Oc. j. japonicus in Asia and the reported expansion of its range in the eastern United States, indicate that it could function as a bridge vector for EEE virus between the enzootic Culiseta melanura (Coquillett)-avian cycle and susceptible mammalian hosts.     

Targeted trapping of mosquito vectors in the Chesapeake Bay area of Maryland

Most adult mosquito surveillance in Maryland is performed using dry ice-baited or unbaited Centers for Disease Control (CDC) miniature light traps suspended approximately 1.5 m above the ground. However, standardized trapping methods may miss mosquito species involved in disease transmission cycles. During a 2-yr study, the effectiveness of the olfactory attractant 1-octen-3-ol alone and in combination with carbon dioxide was evaluated for collecting mosquito vector species. In addition, trap heights were examined to determine the optimal vertical placement to target various species. We evaluated the results during the second year by targeting selected species by using various habitat- height-bait combinations. Although Culex erraticus Dyar & Knab and Anopheles quadrimaculatus Say were not successfully targeted, Culex salinarius Coquillett, Aedes vexans Meigen, Anopheles bradleyi/crucians King, Coquillettidia perturbans Walker, Aedes sollicitans Walker, and Aedes taeniorhynchus Wiedemann were preferentially captured using targeted trapping schemes.     

Comparative susceptibility of Culex tarsalis, Anopheles franciscanus, and Culiseta inornata (Diptera: Culicidae) to Plasmodium relictum (Haemosporidia: Plasmodiiae)

Repeated laboratory attempts failed to infect Culiseta inornata (Williston) and Anopheles franciscanus McCracken with Plasmodium relictum as efficiently as Culex tarsalis Coquillett controls. Of 210 An. franciscanus that imbibed a replete meal from a parasitemic canary, two were found with oocysts and none with sporozoites. Of 112 Cs. inornata similarly fed, seven contained oocysts and one contained sporozoites. In contrast, of 94 Cx. tarsalis tested, 80 (85%) were found with oocysts, thus confirming that this mosquito is a suitable host of P. relictum. Lack of An. franciscanus and Cs. inornata with sporozoites precluded transmission studies and indicated that these species do not play a major role in the maintanance of P. relictum during fall and winter in the Sacramento Valley, Calif.     

Simultaneous field comparison of evening temporal distributions of nectar and blood feeding by Aedes vexans and Ae. trivittatus (Diptera: Culicidae) in Ohio.

Nectar- and blood-feeding time distributions of Aedes vexans (Meigen) and Aedes trivittatus (Coquillett) were determined from collections of mosquitoes attempting to feed on flowers and human bait during six nights in an Ohio field. Distributions of nectar and blood feeding were different in Ae. vexans on three of five nights when analyses were possible, and they were different in pooled Ae. trivittatus data. Higher proportions of blood feeders appeared in earlier time intervals, but both nectar and blood feeding had broadly overlapping peaks and distributions. These results suggest that the nectar- and blood-feeding rhythms are probably in phase in Ae. vexans females, and that possibly the earlier onset of blood feeding reflects a strategy taking advantage of blood when it is available. Male Ae. vexans had later peak nectar-feeding times than females. Nectar feeding in males may be delayed by mating activity early in the activity period.     

Vector competence of Culex tarsalis (Diptera: Culicidae) from Iowa for a sympatric strain of western equine encephalomyelitis (WEE-7738) virus

Experiments were designed to evaluate the vector competence of Culex tarsalis Coquillet from an area (Sioux City) where Cx. tarsalis is most abundant in Iowa for western equine encephalomyelitis virus (WEE-7738). WEE-7738 was isolated from Aedes trivittatus (Coquillet) collected in Ames, IA, in 1977. Infection rate, dissemination rate, multiplication efficiency, and transmission rate were determined for this virus in the SC strain of Cx. tarsalis. SC strain of Cx. tarsalis was as susceptible to WEE-7738 as Californian strains of Cx. tarsalis were to BFS1703 strain of WEE; OID50 of SC Cx. tarsalis was 2.63 log TCID50 per mosquito and OID50 of Californian strains of Cx. tarsalis were 2.0-4.1 log PFU per mosquito. However, transmission of WEE-7738 (4.2%) by the SC strain of Cx. tarsalis was lower than those (10-60%) reported in other studies.     

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.