A winter seasonal biotope of Culex pipiens autogenicus]

The authors describe an epigeal winter seasonal biotope of "culex pipiens autogenicus. The biotope consists of the irrigation system of the large Bervedere park of Tunis city. During the cold and rainy season the irrigation system is abandoned. Many water pools are formed in it in which C. pipiens and Culiseta longiareolata multiply. In summer the operation of the irrigation system brings about the disparition of the nests of larvae. Breeding performed from larvae collected in nature pointed out the autogenous and stenogam characters. Morphologically the specimens correspond to autogenous forms. The importance of the investigations is the evolution of the C. pipiens autogenic species in external nests of larvae during winter was pointed out.     

Larvicidal activity of selected plant hydrodistillate extracts against the house mosquito, Culex pipiens, a West Nile virus vector

The larvicidal activity of hydrodistillate extracts from Chrysanthemum coronarium L., Hypericum scabrum L., Pistacia terebinthus L. subsp. palaestina (Boiss.) Engler, and Vitex agnus castus L. was investigated against the West Nile vector, Culex pipiens L. (Diptera: Culicidae). Yield and identification of the major essential oils from each distillation was determined by GC-MS analyses. The major essential oil component for each plant species was as follows: α-pinene for P. terebinthus palaestina, and H. scabrum (45.3% and 42.3%, respectively), trans-β-caryophyllene for V. agnus castus (22.1%), and borneol for C. coronarium (20.9%). A series of distillate concentrations from these plants (that ranged from 1 ppm to 500 ppm, depending on plant species) were assessed against late third to early fourth C. pipiens larvae at 1, 6, and 24 h posttreatment. In general, larval mortality to water treated with a distillate increased as concentration and exposure time increased. H. scabrum and P. terebinthus palaestina were most effective against the mosquito larvae and both produced 100% mortality at 250 ppm at 24-h continuous exposure compared with the other plant species. Larval toxicity of the distillates at 24 h (LC₅₀ from most toxic to less toxic) was as follows: P. terebinthus palaestina (59.2 ppm) > H. scabrum (82.2 ppm) > V. agnus castus (83.3 ppm) > C. coronarium (311.2 ppm). But when LC₉₀ values were compared, relative toxicity ranking changed as follows: H. scabrum (185.9 ppm) > V. agnus castus (220.7 ppm) > P. terebinthus palaestina (260.7 ppm) > C. coronarium (496.3 ppm). Extracts of native Turkish plants continue to provide a wealth of potential sources for biologically active agents that may be applied against arthropod pests of man and animals.     

The potential of cladocerans as controphic competitors of the mosquito Culex pipiens

This study assesses the potential of cladocerans as competitors for controlling the oviposition and larval abundances of mosquitoes. Control of mosquito larvae involving the use of antagonists has focused mostly on predators. We hypothesized that cladoceran competitors have a strong potential to control larval populations of some species of mosquitoes that can be early colonizers of newly-filled waterbodies, and should be less efficient competitors. To test this hypothesis, the establishment and development of larval populations of wild Culex pipiens were investigated in outdoor microcosms varying in terms of Daphnia magna populations. When the population was well established (i.e., high densities of D. magna), oviposition was fully inhibited and there was consequently no mosquito larvae. When the population was more recently established (i.e., lower densities of D. magna), oviposition and larval development of Cx. pipiens occurred. In the absence of D. magna, oviposition, larval biomass, and abundance of Cx. pipiens reached high values. In this situation, conspecifics were inhibiting further oviposition of Cx. pipiens. Based on these results, we suggest that competing zooplankton species, such as D. magna, could be used for the control of mosquito species such as Cx. pipiens. This approach could be beneficial for the management of wetlands.     

济宁地区淡色库蚊幼虫对苏云金杆菌的抗性水平研究

通过苏云金杆菌对采集的几株野外淡色库蚊种群幼虫的灭杀作用,分析不同环境下,该蚊对苏云金杆菌抗药性的差异.采用幼虫液浸法,测定不同淡色库蚊种群幼虫对苏云金杆菌的LC50.结果显示,苏云金杆菌BTH-14对采集的几株淡色库蚊种群幼虫有不同的灭杀效果,其中采集于苇坑种群的试虫对苏云金杆菌表现出一定程度的抗性,但到F2代,该种...     

A new densovirus isolated from the mosquito Culex pipiens (Diptera: culicidae)

We have isolated from a laboratory strain of Culex pipiens in which abnormal larval mortality occurred a small icosahedral nonenveloped DNA virus sharing the main biological and biophysical properties of densoviruses (DNVs). Unlike DNVs isolated previously from Aedes species, i.e. the AaeDNV and the AalDNV (Afanasiev, B.N., Galyov, E. E., Buchatsky, L.P., Kozlov, Y.V., 1991. Nucleotide sequence and genomic organization of Aedes densonucleosis virus. Virology 185, 323-336; Boublik, Y., Jousset, F.-X., Bergoin, M., 1994. Complete nucleotide sequence and genomic organization of the Aedes albopictus Parvovirus (AaPV) pathogenic for Aedes aegypti larvae. Virology 200, 752-763), this mosquito DNV named CpDNV possesses a genome of 6 kb separately encapsidated in stoichiometric proportion as 'plus' and 'minus' strands. The lack of sequence homology between the CpDNV and the AalDNV genome and of antigenic cross-reactivity between their capsid polypeptides indicates that these two mosquito DNVs are phylogenetically distant. In contrast, the CpDNV appears to be related to the Junonia coenia densovirus (JcDNV) at both serological and genomic levels.     

Tissue localization of overproduced esterases in the mosquito Culex pipiens (Diptera: Culicidae).

We have investigated the tissue distribution of overproduced esterases A (A1 and A2) and B (B1 and B2) in strains of Culex pipiens L. by immunocytochemistry. S-LAB mosquitoes, lacking overproduced esterases, were used as reference. Tissues showing a strong specific reaction (fluorescence) were observed with anti-esterase A1 antiserum in S54 (with A1) and BOUAKE (with A2) strains, and with anti-esterase B1 antiserum in TEM-R and EDIT (with B1) and BOUAKE (with B2) strains. Overproduction of esterases A and B was tissue-specific. The most constant pattern for the two types of esterases was their overproduction in the alimentary canal and Malpighian tubes, although fluorescence varied in intensity depending on strains and developmental stages. There was no difference in the tissue distribution of esterases Al and A2. In contrast, esterases B pattern was highly variable among strains. Differences between TEM-R and EDIT were explained by the different overall overproduction and number of copies of the amplified gene (10-fold higher in TEM-R). The most striking difference in esterase B1 and B2 tissue localization concerned the nervous system where neurons were intenisely fluorescent in TEM-R and EDIT (B1), but not in BOUAKE (B2). All esterase B positive tissues in TEM-R contained large quantities of esterase B1 mRNA (in situ hybridization), indicating that at least part of the protein revealed by immunochemistry was produced in the tissues where it was observed. Our results are discussed in terms of the protection that the different esterases can confer during exposition to organophosphorous insecticides.     

Genetic characterization of a new insect flavivirus isolated from Culex pipiens mosquito in Japan

We found a new flavivirus that is widespread in Culex pipiens and other Culex mosquitoes in Japan. The virus isolate, named Culex flavivirus (CxFV), multiplied only in mosquito cell lines producing a moderate cytopathic effect, but did not grow in mammalian cells. The CxFV genome is single-stranded RNA, 10,834 nt in length and containing a single open reading frame encoding a polyprotein of 3362 aa with 5' and 3' untranslated regions (UTRs) of 91 and 657 nt, respectively. Phylogenetic analyses revealed that CxFV is closely related to the insect flaviviruses associated with Aedes mosquitoes, Cell fusing agent (CFA) and Kamiti River virus (KRV). The 3' UTR of CxFV contains four tandem repeats, which have sequence similarities to the two direct repeats in the CFA and KRV 3' UTRs. These results suggest that CxFV may be a new group of insect flaviviruses.     

Lipid utilization for ovarian development in an autogenous mosquito, Culex pipiens molestus (Diptera: Culicidae)

During the first ovarian cycle, autogenous female mosquitoes develop their ovaries in the absence of blood feeding. In autogenous Culex pipiens molestus (Forskal), complete yolk deposition was observed 2 d after emergence, even when no feeding was allowed (starved). Neutral lipids in Cx. p. molestus increased during the pupal stage, abruptly declined after emergence, and again increased on day 3. In contrast, neutral lipids decreased in anautogenous Anopheles stephensi (Liston) and Cx. p. pallens (Coquillett) and starved females died within 2-3 d after emergence. High ratios of two major neutral lipids, free fatty acid and triglyceride, were isolated by thin-layer chromatography (TLC) from the lipid contents of both Cx. p. molestus and An. stephensi fourth-instars and newly emerged females. Fatty acid analyses using gas liquid chromatography (GLC) and GLC-mass spectrometry (GLC-MS) showed higher proportions of unsaturated than saturated fatty acids in Cx. p. molestus at both stages and two major neutral lipids: free fatty acids and triglycerides. The percentage composition of linoleic acid (C18:2), which is a precursor of arachidonic acid, was higher in Cx. p. molestus than in An. stephensi. Our results indicated that elevated lipid content before emergence may play a role of inducing ovarian development in autogenous mosquitoes.     

Chemical composition and larvicidal evaluation of Mentha, Salvia, and Melissa essential oils against the West Nile virus mosquito Culex pipiens

The volatile metabolites of wild-growing Mentha spicata, M. longifolia, M. suaveolens, Melissa officinalis, Salvia fruticosa, S. pomifera subsp. calycina, and S. pomifera subsp. pomifera from Greece were determined by gas chromatography and gas chromatography–mass spectrometry. The insecticidal properties of the analyzed essential oils were screened on Culex pipiens larvae. Additionally two of the main components of the essential oils, piperitenone oxide and 1,8-cineole were assayed against C. pipiens in order to define the affiliation between them and the larvicidal properties of the oils. The most effective oils were M. suaveolens (major constituent piperitenone oxide, 62.4%), M. spicata (piperitenone oxide, 35.7% and 1,8-cineole, 14.5%) and M. longifolia—Central Greece (piperitenone oxide, 33.4%; 1,8-cineole, 24.5% and trans-piperitone epoxide, 17.4%), which exhibited LC₅₀ values ranging from 47.88 to 59.33 mg l⁻¹. Medium activity revealed the oils of M. officinalis (terpin-4-ol, 15.8%; caryophyllene oxide, 13.2%; sabinene, 12.9%; β-pinene, 12.1%; and trans-caryophyllene, 10.2%), M. longifolia—Southern Greece (carvone, 54.7% and limonene 20.0%), S. pomifera subsp. pomifera (trans-caryophyllene, 22.5% and trans-thujone, 21.0%), S. pomifera subsp. calycina—West Southern Greece (trans-thujone, 56.1% and 1,8-cineole, 10.4%), and S. fruticosa—population 2 (camphor, 23.1%; α-pinene, 12.7%; and borneol, 12.6%), with LC₅₀ values ranging from 78.28 to 91.45 mg l⁻¹. S. pomifera subsp. calycina (Central Greece) essential oil (trans-thujone, 26.5% and cis-thujone, 12.0%) presented rather low activity (LC₅₀ values 140.42 mg l⁻¹), while S. fruticosa—population 1 (1,8-cineole, 31.4% and camphor, 22.6%) was the only inactive oil. Additionally, the constituent piperitenone oxide was found to be highly active (LC₅₀ values 9.95 mg l⁻¹), whereas 1,8-cineole revealed no toxicity.     

An approach to mosquito control: using the dominant attraction of flowering Tamarix jordanis trees against Culex pipiens

In this study, we identified blossoms that attract Culex pipiens L. s.l. in a Mediterranean habitat by using branches of 26 common plant species as baits for traps. The highest catch, 60.5% of the total, by flowers of Tamarix jordanis Boiss., was approximately 6 times greater than the 10.7% caught by flowering Polygonum equisetiforme Sm., and 10 times higher than the 6.6% caught by flowers of Acacia saligna (Lindle) H. L. Wendl. The catch elicited by the other plants ranged between 4.0 and 0.1%. Plant attraction also was evaluated in a field situation. Experimental and control sites were similar strips of vegetation along water channels with T. jordanis trees in the center. In the experimental site, these trees were sprayed with sucrose solution, food dye, and oral insecticide (Spinosad). Concurrently, patches of plant species and trees in the control site were sprayed with solutions of sucrose and different food dye markers. Cx. pipiens populations in both sites were monitored. The highest proportion (65.2%) of the marked mosquitoes in the control site carried the dye of flowering T. jordanis. The dye of flowering P. equisetiforme and that of A. saligna were found, respectively, in 8.1 and 3.5% of the labeled mosquitoes. The marker of reed groups (Phragmites australis [Cav.] Steudel) above the water was found in 19.4% of mosquitoes, whereas the different marker of dry land reeds was found in only 0.4% of the labeled mosquitoes. In the experimental site, after treatment, the mosquitoes decreased from approximately 255 per trap to approximately 24 mosquitoes per trap, whereas the catch in the control site reached approximately 400 mosquitoes per trap.     

Laboratory and field evaluation of the fungus Chrysosporium lobatum against the larvae of the mosquito Culex quinquefasciatus

Eleven fungal species in three genera were isolated from the soil at Agra, India by the feather-baiting technique. Out of the 11 species, Chrysosporium lobatum Scharapov, a deuteromycetous (Moniliales: Moniliaceae) fungus, caused high mortality of Culex quinquefasciatus Say (Diptera: Culicidae) larvae in the laboratory. Laboratory and field trials were carried out to study the efficacy of C. lobatum against various instars of C. quinquefasciatus. In the laboratory bioassays, first, second and third instar larvae were assessed separately. Conidia of C. lobatum that were 15 days old were used both in laboratory and field bioassays. Six different concentrations were used in the laboratory bioassays (10, 10³, 10⁴, 5 × 10⁴, 10⁵ and 10⁶ conidia/mL), and one concentration was tested in the field trials (10⁶ conidia/mL). The LC₅₀ values with 95% fiducial limits and probit equations were calculated by the probit analysis. Significant (analysis o.f variance (ANOVA): P < 0.0001) mortality difference between the instars of C. quinquefasciatus was observed after 72 h of exposure to conidia of C. lobatum. The third instar C. quinquefasciatus were 319- and 25-fold more susceptible to C. lobatum (0.47 × 10³ conidia/mL) than the first and second instars, respectively. The cuticle of the abdominal region and anal papillae were densely covered by the C. lobatum conidia. In the field trials, populations had declined significantly (t test, P = 0.003) 15 days after inoculation in the four test pools. Significantly (t test, P = 0.03) higher mortality was observed in the pools with water quality that was lower in total dissolved solids, hardness, chemical oxygen demand and conductivity. Based on the performance and survival in the trial, C. lobatum may be considered as a bio-control agent of mosquitoes.     

Recent emergence of insensitive acetylcholinesterase in Chinese populations of the mosquito Culex pipiens (Diptera: Culicidae)

Organophosphate/carbamate target resistance has emerged in Culex pipiens L. (Diptera: Culicidae), the vector of Wuchereria bancrofti and West Nile virus (family Flaviviridae, genus Flavivirus) in China. The insensitive acetylcholinesterase was detected in only one of 20 samples collected on a north-to-south transect. According to previous findings, a unique mutation, G119S in the ace-1 gene, explained this high insensitivity. Phylogenetic analysis indicates that the mutation G119S recently detected in China results from an independent mutation event. The G119S mutation thus occurred at least three times independently within the Cx. pipiens complex, once in the temperate (Cx. p. pipiens) and twice in the tropical form (Cx. p. quinquefasciatus). Bioassays performed with a purified G119S strain indicated that this substitution was associated with high levels of resistance to chlorpyrifos, fenitrothion, malathion, and parathion, but low levels of resistance to dichlorvos, trichlorfon, and fenthion. Hence, it is possible that in China, dichlorvos, trichlorfon, and fenthion will still achieve effective control even in the presence of the G119S mutation.     

First record of a mosquito iridescent virus in Culex pipiens L. (Diptera: Culicidae)

The mosquito iridescent viruses (MIVs) are large icosahedral DNA viruses that replicate and assemble in the cytoplasm of the host. Paracrystalline arrangements of virions that accumulate in the cytoplasm produce an iridescent color that is symptomatic of acute infections. In August 2010, we found larvae of Culex pipiens with these symptoms in suburban ditches around the city of La Plata, Argentina. Electron microscope studies, DNA sequencing, and phylogenetic analysis of the major capsid protein confirmed this as the first record of an MIV in C. Pipiens.