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PubMed1997

Effects of rice culture practices on the abundance of Culex mosquitoes (Diptera:Culicidae) in northern Thailand.

In 1991-1993, the density (numbers per 10 dips) and abundance (density x flooded area) of mosquitoes were studied in 3 areas of northern Thailand with different environmental conditions. Culex tritaeniorhynchus Giles, Cx. vishnui Theobald, and Cx. gelidus Theobald were predominant among the 8 Culex species collected. Abundance of these 3 species varied significantly among the 3 areas. Type of habitat classified according to agricultural practices in rainy and dry season significantly influenced larval abundance of Cx. tritaeniorhynchus and Cx. vishnui. Seasonal variation in larval abundance was significant only in Cx. vishnui. The response of the 3 vector mosquitoes to environmental heterogeneity is discussed.

Agriculture↗
PubMed2005

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.

Altitude↗
PubMed2006

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.

Animals↗
PubMed2001

Morphological and molecular evidence that Culex nigripalpus baculovirus is an unusual member of the family Baculoviridae.

We present evidence that a newly discovered mosquito virus from Culex nigripalpus is an unusual member of the family BACULOVIRIDAE: Development of this virus was restricted to nuclei of midgut epithelial cells in the gastric caeca and posterior stomach. The globular occlusion bodies were not enveloped, measured around 400 nm in diameter, occurred exclusively in nuclei of infected cells and typically contained four, sometimes up to eight, virions. The developmental sequence involved two virion phenotypes: an occluded form (ODV) that initiated infection in the midgut epithelial cells, and a budded form that spread the infection in the midgut. Each ODV contained one rod-shaped enveloped nucleocapsid (40x200 nm). The double-stranded DNA genome was approximately 105-110 kbp with an estimated GC content of 52%. We have sequenced approximately one-third of the genome and detected 96 putative ORFs of 50 amino acids or more including several genes considered to be unique to baculoviruses. Phylogenetic analysis of the amino acid sequences of DNApol and p74 placed this virus in a separate clade from the genera NUCLEOPOLYHEDROVIRUS: and GRANULOVIRUS: We provisionally assign this virus in the genus NUCLEOPOLYHEDROVIRUS:, henceforth abbreviated as CuniNPV (for Culex nigripalpus nucleopolyhedrovirus), and suggest that, awaiting additional data to clarify its taxonomic status, it may be a member of a new genus within the family BACULOVIRIDAE:

Amino Acid Motifs↗
PubMed1994

Differential responses of Aedes and Culex mosquitoes to octenol or light in combination with carbon dioxide in Queensland, Australia.

Field studies were conducted with EVS (encephalitis vector surveillance) traps in south-eastern Queensland, Australia, to determine the relative response rates of mosquitoes to three levels (0.1, 4.5 and 30 mg/h) of 1-octen-3-ol (octenol) in combination with a standard bait of 2200 g carbon dioxide (CO2), compared with CO2 alone or CO2 with light from a 6V incandescent bulb. Compared to CO2 alone, Aedes vigilax collections increased significantly when CO2 was supplemented by all three octenol emission levels, but not by the addition of light. Furthermore, the 4.5 and 30 mg/h release rate of octenol gave a significant increase in numbers of Ae.vigilax relative to that from CO2+light. In contrast, collections of Culex annulirostris and Culex sitiens were not enhanced significantly by either the addition of light or octenol at all three levels. Fewer Cx sitiens were collected with octenol released at 4.5 mg/h in comparison to CO2 alone. These differential sampling rates should be taken into account when using EVS traps.

Aedes↗
PubMed2006

Orientation of Culex mosquitoes to carbon dioxide-baited traps: flight manoeuvres and trapping efficiency.

Females of Culex quinquefasciatus Say and Culex tarsalis Coquillet (Diptera: Culicidae) in the host-seeking stage were released and video recorded in three dimensions in a large field wind tunnel as they flew to four kinds of CO2-baited mosquito traps. The trapping efficiency (number of mosquitoes approaching compared to the number caught) was determined for each trap type. The Encephalitis Virus Surveillance (EVS), Mosquito Magnet Freedom (MMF) and Mosquito Magnet Liberty (MML) traps captured only 13-16% of approaching Cx. quinquefasciatus females, whereas the Mosquito Magnet-X (MMX) trap captured 58%. Similar results were obtained for Cx. tarsalis. Orientation behaviour and flight parameters of mosquitoes approaching the four traps were compared. Mosquitoes spent the most time orienting to the EVS trap. Flight speed decreased as mosquitoes entered the vicinity of each trap and a large portion of their time was spent within 30 cm downwind of the traps. Flights became highly tortuous downwind of the poorly performing traps and just upwind of the MMX trap. Differences between traps and possible explanations for the superior performance of the MMX trap are considered.

Animals↗
PubMed2006

Effect of Novaluron (Rimon 10 EC) on the mosquitoes Anopheles albimanus, Anopheles pseudopunctipennis, Aedes aegypti, Aedes albopictus and Culex quinquefasciatus from Chiapas, Mexico.

Dengue fever is a serious problem in Mexico and vector control has not been effective enough at preventing outbreaks. Malaria is largely under control, but it is important that new control measures continue to be developed. Novaluron, a novel host-specific insect growth regulator and chitin synthesis inhibitor, has proved to be effective against agricultural pests, but its efficacy against larval mosquito vectors under field conditions remains unknown. In accordance with the World Health Organization Pesticide Evaluation Scheme, phase I, II and III studies were conducted to evaluate the efficacy and residual effect of Novaluron (Rimon 10 EC, Makhteshim, Beer-Sheva, Israel) on the malaria vectors Anopheles albimanus Wiedemann (Diptera: Culicidae) and Anopheles pseudopunctipennis Theobald, the dengue vectors Aedes aegypti (L) and Aedes albopictus Skuse and the nuisance mosquito Culex quinquefasciatus Say. Laboratory susceptibility tests yielded diagnostic concentrations for all five target species. Field trials to identify the optimum field dosage of Novaluron against Anopheles mosquitoes were carried out under semi-natural conditions in artificial plots and in vessels with wild mosquitoes. Efficacy was measured by monitoring mortality of larvae and pupae and the percentage of inhibition of emergence from floating cages. Dosages of Novaluron for field tests were based on pupal LC(99) (lethal concentration 99%) of An. pseudopunctipennis (0.166 mg/L) in plots and average pupal LC(99) of Ae. aegypti and Ae. albopictus (0.55 mg/L). At all dosages tested, Novaluron significantly reduced larval populations of An. albimanus, Culex coronator Dyar & Knab, Ae. albopictus and Cx. quinquefasciatus by approximately 90%, inhibited adult emergence of An. albimanus and An. pseudopunctipennis by approximately 97% for almost 4 months in experimental plots, and inhibited adult emergence of Ae. aegypti and Ae. albopictus by approximately 97% for up to 14 weeks. Recommended dosages of Novaluron for non-container breeding and container breeding mosquitoes are 0.166 mg/L and 0.55 mg/L, respectively. Overall, the residual effect was more sustained than that of temephos. The lowest dosage of Novaluron had less of an impact on non-target organisms than did temephos. Small-scale field trials in natural breeding sites treated with Novaluron at 0.6 L/ha eliminated adult emergence of An. albimanus and Cx. coronator for 8 weeks. For phase III studies, Novaluron was tested at the local and village levels, applying the optimum field rate to all natural breeding habitats within 1 km of a pair of neighbouring villages. Village-scale trials of Novaluron at 0.6 L/ha reduced An. albimanus larval populations for at least 8 weeks and, more importantly, sharply reduced the densities of adult host-seeking mosquitoes approaching houses. We conclude that Novaluron is effective and environmentally safer than temephos.

Animals↗
PubMed2006

A second independent resistance mechanism to Bacillus sphaericus binary toxin targets its alpha-glucosidase receptor in Culex quinquefasciatus.

The entomopathogen Bacillus sphaericus is an important tool for the vector control of Culex sp., and its effectiveness has been validated in field trials. The appearance of resistance to this bacterium, however, remains a threat to its use, and attempts have been made to understand the resistance mechanisms. Previous work showed that the resistance to B. sphaericus in a Culex quinquefasciatus colony is associated with the absence of the approximately 60-kDa binary toxin receptor in larvae midgut microvilli. Here, the gene encoding the C. quinquefasciatus toxin receptor, Cqm1, was cloned and sequenced from a susceptible colony. The deduced amino-acid sequence confirmed its identity as an alpha-glucosidase, and analysis of the corresponding gene sequence from resistant larvae implicated a 19-nucleotide deletion as the basis for resistance. This deletion changes the ORF and originates a premature stop codon, which prevents the synthesis of the full-length Cqm1. Expression of the truncated protein, however, was not detected when whole larvae extracts were probed with antibodies raised against an N-terminal 45-kDa recombinant fragment of Cqm1. It seems that the premature stop codon directs the mutated cqm1 to the nonsense-mediated decay pathway of mRNA degradation. In-gel assays confirmed that a single alpha-glucosidase protein is missing from the resistant colony. Further in vitro affinity assays showed that the recombinant fragment binds to the toxin, and mapped the binding site to the N-terminus of the receptor.

Amino Acid Sequence↗
PubMed1971

Culex (Melanoconion) aikenii: natural vector in Panama of endemic Venezuelan encephalitis.

Experiments performed in an endemic area of Venezuelan equine encephalitis in the Panama Canal Zone demonstrated transmission of Venezuelan equine encephalitis virus from naturally infected Culex aikenii mosquitoes to laboratory hamsters. Results of experiments indicate that Culex aikenii is an efficient natural vector and the principal species of mosquito transmitting Venezuelan equine encephalitis in this endemic zone.

Animals↗
PubMed1986

Amplification of an esterase gene is responsible for insecticide resistance in a California Culex mosquito.

An esterase gene from the mosquito Culex quinquefasciatus that is responsible for resistance to a variety of organophosphorus (OP) insecticides was cloned in lambda gt11 phage. This gene was used to investigate the genetic mechanism of the high production of the esterase B1 it encodes in OP-resistant Culex quinquefasciatus Say (Tem-R strain) from California. Adults of the Tem-R strain were found to possess at least 250 times more copies of the gene than adults of a susceptible strain (S-Lab). The finding that selection by pesticides may result in the amplification of genes encoding detoxifying enzymes in whole, normally developed, reproducing insects emphasizes the biological importance of this mechanism and opens new areas of investigation in pesticide resistance management.

Animals↗
PubMed1999

Production of Cry11A and Cry11Ba toxins in Bacillus sphaericus confers toxicity towards Aedes aegypti and resistant Culex populations.

Cry11A from Bacillus thuringiensis subsp. israelensis and Cry11Ba from Bacillus thuringiensis subsp. jegathesan were introduced, separately and in combination, into the chromosome of Bacillus sphaericus 2297 by in vivo recombination. Two loci on the B. sphaericus chromosome were chosen as target sites for recombination: the binary toxin locus and the gene encoding the 36-kDa protease that may be responsible for the cleavage of the Mtx protein. Disruption of the protease gene did not increase the larvicidal activity of the recombinant strain against Aedes aegypti and Culex pipiens. Synthesis of the Cry11A and Cry11Ba toxins made the recombinant strains toxic to A. aegypti larvae to which the parental strain was not toxic. The strain containing Cry11Ba was more toxic than strains containing the added Cry11A or both Cry11A and Cry11Ba. The production of the two toxins together with the binary toxin did not significantly increase the toxicity of the recombinant strain to susceptible C. pipiens larvae. However, the production of Cry11A and/or Cry11Ba partially overcame the resistance of C. pipiens SPHAE and Culex quinquefasciatus GeoR to B. sphaericus strain 2297.

Aedes↗
PubMed2001

Various levels of cross-resistance to Bacillus sphaericus strains in Culex pipiens (Diptera: Culicidae) colonies resistant to B. sphaericus strain 2362.

We studied the cross-resistance to three highly toxic Bacillus sphaericus strains, IAB-59 (serotype H6), IAB-881 (serotype H3), and IAB-872 (serotype H48), of four colonies of the Culex pipiens complex resistant to B. sphaericus 2362 and 1593, both of which are serotype H5a5b strains. Two field-selected highly resistant colonies originating from India (KOCHI, 17,000-fold resistance) and France (SPHAE, 23,000-fold resistance) and a highly resistant laboratory-selected colony from California (GeoR, 36,000-fold resistance) showed strong cross-resistance to strains IAB-881 and IAB-872 but significantly weaker cross-resistance to IAB-59 (3- to 43-fold resistance). In contrast, a laboratory-selected California colony with low-level resistance (JRMM-R, 5-fold resistance) displayed similar levels of resistance (5- to 10-fold) to all of the B. sphaericus strains tested. Thus, among the mosquitocidal strains of B. sphaericus we identified a strain, IAB-59, which was toxic to several Culex colonies that were highly resistant to commercial strains 2362 and 1593. Our analysis also indicated that strain IAB-59 may possess other larvicidal factors. These results could have important implications for the development of resistance management strategies for area-wide mosquito control programs based on the use of B. sphaericus preparations.

Animals↗
PubMed2003

Introduction of Culex toxicity into Bacillus thuringiensis Cry4Ba by protein engineering.

Bacillus thuringiensis mosquitocidal toxin Cry4Ba has no significant natural activity against Culex quinquefasciatus or Culex pipiens (50% lethal concentrations [LC(50)], >80,000 and >20,000 ng/ml, respectively). We introduced amino acid substitutions in three putative loops of domain II of Cry4Ba. The mutant proteins were tested on four different species of mosquitoes, Aedes aegypti, Anopheles quadrimaculatus, C. quinquefasciatus, and C. pipiens. Putative loop 1 and 2 exchanges eliminated activity towards A. aegypti and A. quadrimaculatus. Mutations in a putative loop 3 resulted in a final increase in toxicity of >700-fold and >285-fold against C. quinquefasciatus (LC(50) congruent with 114 ng/ml) and C. pipiens (LC(50) 37 ng/ml), respectively. The enhanced protein (mutein) has very little negative effect on the activity against Anopheles or AEDES: These results suggest that the introduction of short variable sequences of the loop regions from one toxin into another might provide a general rational design approach to enhancing B. thuringiensis Cry toxins.

Aedes↗
PubMed2003

Infection of malaria (Anopheles gambiae s.s.) and filariasis (Culex quinquefasciatus) vectors with the entomopathogenic fungus Metarhizium anisopliae.

BACKGROUND: Current intra-domiciliary vector control depends on the application of residual insecticides and/or repellents. Although biological control agents have been developed against aquatic mosquito stages, none are available for adults. Following successful use of an entomopathogenic fungus against tsetse flies (Diptera: Glossinidae) we investigated the potency of this fungus as a biological control agent for adult malaria and filariasis vector mosquitoes. METHODS: In the laboratory, both sexes of Anopheles gambiae sensu stricto and Culex quinquefasciatus were passively contaminated with dry conidia of Metarhizium anisopliae. Pathogenicity of this fungus for An. gambiae was further tested for varying exposure times and different doses of oil-formulated conidia. RESULTS: Comparison of Gompertz survival curves and LT50 values for treated and untreated specimens showed that, for both species, infected mosquitoes died significantly earlier (p < 0.0001) than uninfected control groups. No differences in LT50 values were found for different exposure times (24, 48 hrs or continuous exposure) of An. gambiae to dry conidia. Exposure to oil-formulated conidia (doses ranging from 1.6 x 10(7) to 1.6 x 10(10) conidia/m2) gave LT50 values of 9.69 +/- 1.24 (lowest dose) to 5.89 +/- 0.35 days (highest dose), with infection percentages ranging from 4.4-83.7%. CONCLUSION: Our study marks the first to use an entomopathogenic fungus against adult Afrotropical disease vectors. Given its high pathogenicity for both adult Anopheles and Culex mosquitoes we recommend development of novel targeted indoor application methods for the control of endophagic host-seeking females.

Age Factors↗
PubMed2001

Platelet-activating-factor-hydrolyzing phospholipase C in the salivary glands and saliva of the mosquito Culex quinquefasciatus.

A phospholipase C activity specific for platelet-activating factor (PAF), named PAF phosphorylcholine hydrolase, was found in the salivary glands and saliva of the human-feeding mosquito Culex quinquefasciatus. The enzymatic activity was demonstrated by inhibition of PAF-induced platelet aggregation, and by identification of substrate consumption and production of diacyl glyceride by electrospray-ionisation mass spectrometry. The activity has a neutral optimal pH and an apparent molecular mass of 40-50 kDa. Two anthropophilic mosquito species, Aedes aegypti and Anopheles gambiae, do not have this salivary activity. The results are interpreted within the evolutionary context of the genera Culex, Aedes and Anopheles.

Animals↗
PubMed2003

Binding properties of Bacillus thuringiensis Cry1C delta-endotoxin to the midgut epithelial membranes of Culex pipiens.

The Cry1C delta-endotoxin from Bacillus thuringiensis is toxic to both lepidopteran and dipteran insect larvae. To analyze the dipteran-specific insecticidal mechanisms, we investigated the properties of Cry1C binding to the epithelial cell membrane of the larval midgut from the mosquito Culex pipiens in comparison with dipteran-specific Cry4A. Immunohistochemical staining of the larval midgut sections from Culex pipiens showed that Cry1C and Cry4A bound to the microvilli of the epithelial cells. The Cry1C binding to brush border membrane vesicles from the mosquito larvae was specific and irreversible, and did not compete with Cry4A. By ligand blotting analyses, we detected several Cry1C-binding proteins, the Cry1C binding to which did compete with excess unlabeled Cry4A. These results suggested that Cry1C and Cry4A recognized the same binding site(s) on the epithelial cell surface but that their interaction with the target membrane differed.

Animals↗
PubMed1990

Peroral susceptibility of Aedes albifasciatus and Culex pipiens complex mosquitoes (Diptera: Culicidae) from Argentina to western equine encephalitis virus.

The transmission cycle of western equine encephalitis (WEE) virus in South America is unknown. A WEE virus strain was isolated from Aedes albifasciatus in Argentina during the WEE epizootic of 1982-83. Also, Culex pipiens from Argentina was reported to be able to transmit WEE virus experimentally, but other results indicate that Cx. pipiens from the USA is refractory to this virus. We determined the susceptibility of Argentina strains of Ae. albifasciatus and Culex pipiens complex mosquitos to infection by WEE virus by the oral route. Adult females were fed on chicks infected with a WEE virus strain isolated in Cordoba Province, Argentina, or were fed on a blood/virus suspension. Each mosquito ingested between 10(1.6) to 10(6.4) vero cell plaque-forming units of virus. Each of 28 Ae. albifasciatus was positive for virus from the fourth day postfeeding, and there was evidence for virus replication. In contrast, 0/44 Cx. p. quinquefasciatus and only 1/15 Cx. p. pipiens was positive. Aedes albifasciatus is susceptible to infection by WEE virus and should be considered a potential vector of this virus in Argentina. Both subspecies of Cx. pipiens are refractory to peroral infection by WEE virus and probably do not play a role in the WEE virus cycle in Argentina.

Aedes↗
PubMed1995

Studies on mosquitoes (Diptera: Culicidae) and anthropic environment. 8--Survey of adult behaviour of Spissipes Section species of Culex (Melanoconion) in south-eastern Brazil.

A study of Spissipes Section of Culex (Melanoconion) adults behaviour was carried out from August 1992 through December 1993 in human dominated (anthropic) environment in the Ribeira Valley, S. Paulo State, Brazil. By sampling at several sites it the dominance of Culex ribeirensis and Cx. sacchettae became evident even through a total number of ten species was recorded. Those two mosquitoes showed a clear tendency to frequent the domiciliary environment where they were caught, both indoor and outdoor, through the use of the human bait. In the outside environments, the residual patchy forests seems to display a concentration role, from which these adults spread to the open land and reach the dwellings. As their vector competence has been demonstrated through the virus isolations in natural conditions, it is advisable to pay attention to the presence of these mosquitoes in the man-made environment.

Animals↗