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PubMed2005

No evidence for bacteriophage WO orf7 correlation with Wolbachia-induced cytoplasmic incompatibility in the Culex pipiens complex (Culicidae: Diptera).

Gene flow between populations of Culex pipiens L. is relevant to observed differences in disease transmission, insecticide resistance, behavior, and physiology. Intracellular Wolbachia bacteria have been hypothesized to affect gene flow in insects. Specifically, Wolbachia cause a form of embryonic mortality known as cytoplasmic incompatibility (CI) in crosses between individuals with different Wolbachia types. Incompatibility in Culex is exceptional in that it represents the most complex CI pattern known, and yet Culex populations are not infected with divergent Wolbachia strains. This has led to the hypothesis that extrachromosomal factors such as phages or mobile genetic elements may be involved in determining CI phenotype. Recent molecular characterization of Culex laboratory strains has identified variation in the orf7 locus of the Wolbachia-associated bacteriophage WO. Here, crosses between eight Culex strains differing in their orf7 type were conducted to examine for the hypothesized involvement of bacteriophage WO in determining CI in Culex. Although crossing results show examples of compatibility, partial compatibility, and incompatibility, the results fail to show a correlation between the CI phenotypes and orf7 type. Specific examples include high egg hatch resulting in crosses between Culex strains that differ significantly in their orf7 type and low egg hatch resulting in crosses between Culex strains with similar orf7 types. Thus, the phage orf7 locus alone cannot predict CI type in the Culex strains examined in this study. However, rejection of the hypothesized role of WO phage in Culex CI will require the characterization of additional phage loci.

Animals↗
PubMed1994

Host feeding patterns of Culex vishnui sub group of mosquitoes in Dibrugarh district of Assam.

The host feeding patterns of three species of mosquitoes belonging to vishnui sub group, Culex tritaeniorhynchus, Culex vishnui and Culex pseudovishnui, the most prevalent species in Dibrugarh district were determined by analysing their blood meals. All 3 species were found be essentially zoophilic. High percentage of pig feeding was observed in Culex tritaeniorhynchus (40 per cent) and Culex vishnui (35.3 per cent) in comparison to other prevalent species in this area. In contrast Culex pseudovishnui another member of this group was not attracted to pigs (0.4 per cent). Few human feeds were recorded for Culex tritaeniorhynchus (0.4 per cent), Culex vishnui (0.4 per cent) and Culex pseudovishnui (0.8 per cent), indicating their occasional contact with human hosts. Considering the importance of this group as proven vectors of Japanese encephalitis the relevance of these results to JE transmission in this area are discussed.

Animals↗
PubMed2000

Definition of species in the Culex sitiens subgroup (Diptera: Culicidae) from Papua New Guinea and Australia.

Japanese encephalitis is a disease of major importance in Asia, which from 1995 has extended its range into the north of Australia. Culex annulirostris Skuse of the Culex sitiens subgroup of Culex was incriminated as the most likely mosquito vector. Because misidentifications previously have occurred within this subgroup, our paper defines electrophoretic methods to identify Culex specimens from Queensland and the Northern Territory in Australia and from Western Province in Papua New Guinea. In collections from 1996 to 1998 Culex sitiens Wiedemann, Cx. palpalis Taylor, and Cx. annulirostris comprised 93.1% of the total banded proboscis Culex mosquitoes collected; 6.9% remained unidentified to species by morphological or electrophoretic examination. The prevalence of Cx. palpalis was variable and appeared to be associated with below average rainfall during 1997. In Papua New Guinea, this species comprised up to 97.4% of banded proboscis Culex, with smaller numbers collected from the Torres Strait Islands and Cape York; none was collected from other Queensland localities. Cx. annulirostris was more prevalent during years of average or above average rainfall and was predominant in most localities, especially in the Torres Strait and Queensland. These data confirmed the problems in separating Cx. sitiens from Cx. palpalis and Cx. annulirostris using morphological characters.

Alleles↗
PubMed2003

[Appraisal on method of temperature to the first appearance of Culex tritaeniorhynchus in spring].

OBJECTIVE: To find out an appraisal method of temperature on the first appearance date of Culex tritaeniorhynchus in spring. METHODS: Whole night collection of mosquitoes mosquitoes (from 18:00 hours to 06:00 hours of the following day) with light traps had been carried out in pig sties every night since 1 March in 1982 - 1992 and 2001 - 2002 in Fengxian area Shanghai. The adult mosquitoes caught were anaesthetized, then identified and counted. The density of mosquitoes was calculated by the average number of mosquitos per one trap and one night. Comparative analysis of the mean daily air temperature at 7 days before, the first appearance date and 1 day after, the first appearance date of Culex tritaeniorhynchus. RESULTS: Data of the first appearance data of Culex tritaeniorhynchus were judged to mean daily air temperature and cumulative temperature on the day of the first appearance of Culex tritaeniorhynchus and the day before appearance, or 3 days on the day of the first appearance of Culex tritaeniorhynchus and the two days before appearance and the day since appearance with a difference less than 1 - 2 day (91.7%). CONCLUSION: The first appearance of Culex tritaeniorhynchus in spring accompanied with a course of influence by the severe warm air advection from south of China, and lowest mean daily air temperature of the first appearance was 11 degrees. Thus the first appearance data of Culex tritaeniorhynchus could be deduced and rehabilitated from observed values of mean daily air temperature or its forecasting values.

Animals↗
PubMed2004

Culex mosquitoes in temporary urban rain pools: seasonal dynamics and relation to environmental variables.

The study was conducted in a park of Buenos Aires City, where a total of 89 rain pools were sampled weekly for mosquito immature stages over a one-year period. The aim of the present paper was to investigate the seasonal dynamics of three Culex species breeding in temporary rain pools and to analyze the relationships of the presence of these species to pool dimensions, pool age, vegetation, and insolation degree. The three species showed differences in their seasonal patterns, Culex dolosus being present during the whole year, Culex pipiens mainly in the summer season, and Culex maxi almost exclusively during the fall. The variable explaining most of the variation among sampling dates in species composition was weekly mean temperature. A significant positive association was detected among mosquito species, as they were recorded together more frequently than expected by chance. The statistical analyses performed revealed significant positive relationships of all three mosquito species to increasing surface area, whereas no relationship to insolation degree was detected in the studied pools. Culex pipiens and Culex dolosus showed positive relationships to increasing vegetation cover, whereas the presence of Culex dolosus was also related to pool age.

Animals↗
PubMed2001

Stable, germ-line transformation of Culex quinquefasciatus (Diptera: Culicidae).

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.

Aedes↗
PubMed1977

Identification of Culex species by electrophoresis.

This paper extends the usefulness of polyacrylamide gel electrophoresis to studies of mosquito taxonomy and mosquito vector ecology. Using a newly developed double staining technique, it is possible to unambiguously separate several species of Culex mosquitoes found in northern Indiana. These include Culex restuans, Culex pipiens pipiens, and Culex territans. Preliminary work indicates that Culex pipiens quinquefasciatus and Culex salinarius can also be identified by this method. This technique enables precise taxonomic identification of individual mosquitoes or pooled samples whether intact or damaged beyond identification by standard taxonomic methods. The small sample required (20 microliter) per pool leaves sufficient material for virus isolation techniques.

Animals↗
PubMed2004

Evaluation of various attributes of gravid female traps for collection of Culex in Florida.

Gravid female traps are used for surveillance of populations of Culex spp. and arboviruses such as West Nile virus. Field trials evaluating various attributes of gravid female traps for collection of gravid Culex were conducted in rural habitats in Alachua and Marion Counties, FL. Screened cage tests in the field were also used to compare trap models. Three trap models were evaluated: two based on the original Reiter design (Gravid CDC traps A and B) and one based on the revised Reiter design (gravid box trap). Trap model significantly affected collection of Culex quinquefasciatus and Culex nigripalpus; the greatest numbers were collected by the CDC gravid trap Aand CDC gravid trap B traps compared to the gravid box traps. There were no statistically significant differences between the collections with CDC gravid traps A and B. These patterns were similar at both sites and between early and late summer collections in Marion Co. In trials conducted in screened field cages with gravid Cx. quinquefasciatus, significantly more mosquitoes were collected in the CDC gravid trap A and B than in box gravid traps. Size of pan associated with the gravid traps was important and traps with larger pans collected more mosquitoes. Pan color was also important in efficacy of traps, and traps with darker pans (black, green) collected more mosquitoes than traps with lighter pans (tan, white). The percentages of gravid mosquitoes in trap collections of Culex females ranged from 54.0% to 89.6% with no clear differences between model of trap, size of pan, or pan color. Various attributes of gravid female traps impact the efficacy of the traps for Culex spp. and these should be considered in trapping programs.

Animals↗
PubMed2006

Efficacy of four trap types for detecting and monitoring Culex spp. in north central Florida.

The effectiveness of four types of mosquito traps at sampling Culex mosquitoes was compared at two north central Florida study sites (a commercial dairy and a swine research unit) with highly eutrophic lagoons that have a history of producing large populations of Culex mosquitoes. Traps evaluated included a John Hock (JH) model 1012 CDC style light trap, JH model 1712 CDC Gravid Trap (GT), and American Biophysics Corporation's Mosquito Magnet-Experimental (MM-X) and commercial model MM-Professional (MM-Pro) traps. The MM-X and MM-Pro traps are based on new counterflow technology. Culex nigripalpus Theobald and Culex quinquefasciatus Say were the two most abundant species collected, and they were the dominant species at the dairy site and swine research unit, respectively. Culex erraticus Dyar & Knabb and Culex salinarius Coquillett also were caught but in much lower numbers than the two dominant species at the swine unit, and rarely at the dairy site. At the dairy site the MM-Pro collection of total female Cx. quinquefasciatus was significantly greater than all other trap types (MM-Pro > GT > MM-X = CDC), and the MM-Pro also caught the most Cx. nigripalpus, but not significantly more than the CDC or MM-X (MM-Pro = CDC = MM-X > GT). At the swine research unit the largest number of female Cx. quinquefasciatus were caught in the MM-X trap, but the only significant difference was with the CDC trap (MM-X = MM-Pro = CT > CDC). For Cx. nigripalpus the CDC trap caught the most females, but these collections were only significantly different from the MM-Pro and GT (CDC = MM-X > MM-Pro > GT). The GT caught significantly more gravid female Cx. quinquefasciatus than all the other trap types at both sites, but collected very few gravid Cx. nigripalpus at either site.

Animals↗
PubMed2006

Spatially targeting Culex quinquefasciatus aquatic habitats on modified land cover for implementing an Integrated Vector Management (IVM) program in three villages within the Mwea Rice Scheme, Kenya.

BACKGROUND: Continuous land cover modification is an important part of spatial epidemiology because it can help identify environmental factors and Culex mosquitoes associated with arbovirus transmission and thus guide control intervention. The aim of this study was to determine whether remotely sensed data could be used to identify rice-related Culex quinquefasciatus breeding habitats in three rice-villages within the Mwea Rice Scheme, Kenya. We examined whether a land use land cover (LULC) classification based on two scenes, IKONOS at 4 m and Landsat Thematic Mapper at 30 m could be used to map different land uses and rice planted at different times (cohorts), and to infer which LULC change were correlated to high density Cx. quinquefasciatus aquatic habitats. We performed a maximum likelihood unsupervised classification in Erdas Imagine V8.7 and generated three land cover classifications, rice field, fallow and built environment. Differentially corrected global positioning systems (DGPS) ground coordinates of Cx. quinquefasciatus aquatic habitats were overlaid onto the LULC maps generated in ArcInfo 9.1. Grid cells were stratified by levels of irrigation (well-irrigated and poorly-irrigated) and varied according to size of the paddy. RESULTS: Total LULC change between 1988-2005 was 42.1 % in Kangichiri, 52.8 % in Kiuria and and 50.6 % Rurumi. The most frequent LULC changes was rice field to fallow and fallow to rice field. The proportion of aquatic habitats positive for Culex larvae in LULC change sites was 77.5% in Kangichiri, 72.9% in Kiuria and 73.7% in Rurumi. Poorly - irrigated grid cells displayed 63.3% of aquatic habitats among all LULC change sites. CONCLUSION: We demonstrate that optical remote sensing can identify rice cultivation LULC sites associated with high Culex oviposition. We argue that the regions of higher Culex abundance based on oviposition surveillance sites reflect underlying differences in abundance of larval habitats which is where limited control resources could be concentrated to reduce vector larval abundance.

Animals↗
PubMed2001

Transmission efficiency of Culex quinquefasciatus and Aedes aegypti to Wuchereria bancrofti infection: an experimental study.

Present study was undertaken to evaluate the suitability of natural (Culex quinquefasciatus) and experimental (Aedes aegypti) vectors for supporting the development of W. bancrofti larvae for onward transmission. Both the species permitted development of W. bancrofti mf to infective larvae (L3) within 11 to 13 days. The mf intake by both the species of mosquitoes was directly related to mf density in donor's blood. Culex exhibited higher L3 recovery than Aedes. In Aedes maximum percent L3 development occurred after ingesting 4 mf whereas Culex exhibited best establishment at an average mf intake of 11.5. Nevertheless wide variation in mf density in donor's blood did not significantly affect the larval establishment in Aedes mosquito while in Culex very high (> 400 mf/40 microliters) or low (< 50 mf/40 microliters) mf counts in donor's blood adversely affected the L3 recovery. The results reveals that A. aegypti has an edge over the natural vector, Culex in being a voracious feeder, their easy laboratory maintenance and better transmission potential.

Aedes↗
PubMed1993

[A study on transmission of dengue virus by Culex fatigans].

Patients with acute dengue fever within 2 days of onset were simultaneously bitten by Culex fatigans, Aedes aegypti and Aedes albopictus, which were fed and incubated in the laboratory. Isolation and quantitative assay of dengue virus and transmission experiment were conducted on specimens collected from 3 kinds of mosquitoes at different time. The result showed a positive rate of 5.13% (2/39) and an average viral titer of 2.41 logTCID50, for Culex fatigans, which indicates that Culex fatigans might be naturally infected with dengue virus and might transmit dengue virus after infection. But the positive rate and infection rate of Culex fatigans were significantly lower than those of Aedes aegypti and Aedes albopitus, which indicates that Culex fatigans might play a less important role in the transmission of dengue virus.

Aedes↗
PubMed1996

Revision of the Spissipes Section of Culex (Melanoconion) (Diptera:Culicidae).

Twenty-two species in the Spissipes Section of Culex (Melanoconion) are recognized and two taxonomic changes are made: Culex alvarezi Sutil Oramas, Pulido Florenzano and Amarista Meneses is synonymized with Culex spissipes (Theobald), and Culex nicaroensis Duret has been determined not to belong to the subgenus Melanoconion and is here treated as a member of the genus Culex without subgeneric assignment. Descriptions of adult female and male, female cibarium, and genitalia of both sexes are provided. Eight groups and three subgroups are characterized. Available data on distribution and bionomics of each species are given. Maps showing the entire known range of the species are given. Keys for species identification based or morphological characters of adults and male genitalia are provided.

Animals↗
PubMed1987

Overproduction of detoxifying esterases in organophosphate-resistant Culex mosquitoes and their presence in other insects.

Antisera raised against the denatured polypeptide of two organophosphate-detoxifying esterases (B1 and A1) of Culex mosquitoes were used in an immunoblot method to quantify esterase production in resistant versus susceptible strains and to detect the presence of immunologically related proteins in other insects. It was demonstrated that esterase B1 of Culex quinquefasciatus and esterase A1 of Culex pipiens are overproduced in resistant strains by factors of at least 500-fold and 70-fold, respectively, as compared with the corresponding susceptible strains. These factors approximate the levels of resistance to the organophosphate chlorpyrifos determined by bioassay--i.e., about 800-fold and 100-fold, respectively. Antiesterase B1 antiserum was found to react with other type B esterases (B2 of C. quinquefasciatus and B3 of Culex tarsalis) but not with type A esterases (A1 of C. pipiens, A2 of C. quinquefasciatus, or A3 of C. tarsalis); similarly, antiesterase A1 antiserum was found to react with other type A esterases (A2 and A3) but not with type B esterases (B1, B2, and B3). Proteins immunologically related to esterase B1 were detected in Aedes aegypti L., Myzus persicae Sultzer, and Musca domestica L., although they were not overproduced in the organophosphate-resistant strains of these species. In none of these species were proteins immunologically related to esterase A1 found.

Animals↗
PubMed1995

Mosquito carboxylesterase Est alpha 2(1) (A2). Cloning and sequence of the full-length cDNA for a major insecticide resistance gene worldwide in the mosquito Culex quinquefasciatus.

Organophosphorus insecticide resistance in Culex mosquitoes is commonly caused by increased activity of one or more esterases. The commonest phenotype involves elevation of the esterases Est alpha 2 (A2) and Est beta 2 (B2). A cDNA encoding the Est alpha 2 esterase has now been isolated from a Sri Lankan insecticide-resistant mosquito (Culex quinquefasciatus, Say) expression library. In line with a recently suggested nomenclature system (Karunaratne, S. H. P. P. (1994) Characterization of Multiple Variants of Carboxylesterases Which Are Involved in Insecticide Resistance in the Mosquito Culex quinquefasciatus. Ph.D. thesis, University of London), as the first sequenced variant of this esterase, it is now referred to as Est alpha 2(1). The full-length cDNA of est alpha 2(1) codes for a 540-amino acid protein, which has high homology with other esterases and lipases and belongs to the serine or B-esterase enzyme family. The predicted secondary structure of Est alpha 2(1) is similar to the consensus secondary structure of proteins within the esterase/lipase family where the secondary and tertiary structures have been resolved. The level of identity (approximately 47% at the amino acid level) between the est alpha 2(1) and the various Culex est beta (B1 and B2) cDNA alleles that have been cloned and sequenced suggests that the two esterase loci are closely related and arose originally from duplication of a common ancestral gene. The lack of a distinct hydrophobic signal sequence for Est alpha 2(1) and two possible N-linked glycosylation sites, both situated close to the active site serine, suggest that it is a nonglycosylated protein that is not exported from the cell. Southern and dot blot analysis of genomic DNA from various insecticide-resistant and susceptible mosquito strains show that the est alpha 2(1) gene, like est beta 2(1), is amplified in resistant strains. The restriction fragment length polymorphism patterns, after probing Southern blots of EcoRI-digested genomic DNA with esta alpha 2(1) cDNA, show that the amplified and nonamplified est alpha alleles differ in the resistant and susceptible Sri Lankan mosquitoes.

Amino Acid Sequence↗
PubMed2004

Molecular discrimination of Wolbachia in the Culex pipiens complex: evidence for variable bacteriophage hyperparasitism.

The medically important members of the Culex pipiens species complex provide an enigma for systematists, evolutionary biologists, and vector biologists. The species complex is composed of forms that differ in their ecology, behaviour, physiology and vector competence. Cytoplasmic incompatibility (CI) caused by endosymbiotic Wolbachia bacteria is thought to play an important role in restricting gene flow and the evolution of the Culex complex. Here we describe the first molecular marker useful for discriminating between Wolbachia infections in Culex. A putative bacteriophage locus (orf7) varies between Culex forms in copy number and sequence. We provide evidence that the orf7 loci are strictly associated with Wolbachia and are maternally inherited.

Amino Acid Sequence↗
PubMed2001

The salivary adenosine deaminase activity of the mosquitoes Culex quinquefasciatus and Aedes aegypti.

A cDNA coding for a protein with significant similarity to adenosine deaminase (ADA) was found while randomly sequencing a cDNA library constructed from salivary gland extracts of adult female Culex quinquefasciatus. Prompted by this result, we found high ADA activities in two culicine mosquitoes, Culex quinquefasciatus and Aedes aegypti, but not in the anopheline Anopheles gambiae. Homogenates from Culex quinquefasciatus also have an AMP deaminase activity that is three times greater than the ADA activity, whereas in Aedes aegypti the AMP deaminase activity is less than 10% of the ADA activity. Evidence for secretion of ADA during blood feeding by Aedes aegypti includes the presence of ADA activity in warm solutions probed through a membrane by mosquitoes and in serotonin-induced saliva and a statistically significant reduction in the levels of the enzyme in Aedes aegypti following a blood meal. We could not demonstrate, however, that C. quinquefasciatus secrete ADA in their saliva. Male Aedes aegypti and C. quinquefasciatus, which do not feed on blood, have less than 3% of the levels of ADA found in females. We propose that ADA activity in A. aegypti may help blood feeding by removing adenosine, a molecule associated with both the initiation of pain perception and the induction of mast cell degranulation in vertebrates, and by producing inosine, a molecule that potently inhibits the production of inflammatory cytokines. The role of salivary ADA in Culex quinquefasciatus remains unclear.

AMP Deaminase↗
PubMed2003

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.

Animals↗