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Hepatozoon is a very diverse genus with more than 300 species currently assigned to it, basedlargely on morphological characters, host specify and life cycle patterns. Peripheral blood smearsof naturally infected vipers Cerastes cerastes cerastes (hornless) showed intracytoplassmicbanana-shaped gametocytes in the erythrocytes. Upon initial examination in 12% out of 100 collectedvipers harbored Hepatozoon sp. Effect of Hepatozoon sp. infection on some biological parametersof Culex pipiens complex showed no significant difference between longevity of noninfectedand infected ones, and between mortality rate, and pre-oviposition period of both. Fertilityfemale mosquitoes were significantly affected. Infected females produced significantlyfewer eggs/female as compared to those deposited by non-infected ones, without significant differenceincubation periods of eggs deposition. The mean oviposition rate of fully engorged infectedCx. pipiens complex female was highly significant less than that of non-infected femaleones. Statistical analysis revealed a highly significant difference (P

Aquatain® is an alternative larvicide formulation to the currently used larvicides. Its efficacy can be assessed monitoring emerging adults with a floating device that was recently developed for use in catch basins. In this study, the efficacy of Aquatain in controlling Aedes albopictus and Culex pipiens complex was investigated by comparing the adults emerging from 25 treated catch basins with that of 25 control basins in northeastern Italy. Basins were monitored weekly for 9 times and the efficacy was evaluated using the Mann–Whitney U-test and calculating the inhibition of emergence at each sampling. Aquatain was effective in reducing the number of emerging mosquitoes for both species, but its duration was affected by rainfall. Intensive showers (>10 mm daily) seem to reduce the efficacy of the product, allowing an increase in emerging adults after about 2 wk. This finding suggests that climatic factors should be taken into account to decide the right time for reapplication of Aquatain during routine larval treatments.

The Culicinae is the most extensive subfamily among the Culicidae family of mosquitoes. Two genera, Culex and Aedes, from this subfamily have world-wide distribution and are responsible for transmitting of several deadly diseases including Zika, West Nile fevers, chikungunya, dengue, and Rift Valley fevers. Developing high-quality genome assembly for mosquitoes, studying their population structure, and evolution can help to facilitate the development of new strategies for vector control. Studies on Aedes albopitcus as well as on species from the Culex pipiens complex, which are widely spread in the United States, provide excellent models on these topics. Ae. albopictus is one of the most dangerous invasive mosquito species in the world that transmits more than 20 arboviruses. This species has highly repetitive genome that is the largest among mosquito genomes sequenced so far. Thus, sequencing and assembling of such genome is extremally challenging. As a result, the lack of high-quality Ae. albopictus genome assembly has delayed the progress in understanding its biology. To produce a high-quality genome assembly, it was important to anchor genomic scaffolds to the cytogenetic map creating a physical map of the genome assembly. We first developed a new gene-based approach for the physical mapping of repeat-rich mosquito genomes. The approach utilized PCR amplification of the DNA probes based on complementary DNA (cDNA) that does not include repetitive DNA sequences. This method was then used for the development of a physical map for Ae. albopictus based on the in situ hybridization of fifty cDNA fragments or gene exons from twenty-four scaffolds to the mitotic chromosomes from imaginal discs. This study resulted in the construction of a first physical map of the Ae. albopictus genome as well as mapping viral integration and polyphenol oxidase genes. Moreover, comparing our present Ae. albopictus physical map to the current Ae. aegypti assembly indicated the presence of multiple chromosomal inversions between them. To better understand population structure and chromosome evolution in Culicinae mosquitoes, especially in the Culex pipiens complex, we studied genomic and chromosomal differentiation between two subspecies Cx. pipiens pipiens and Cx. pipiens molestus. For the species responsible for the spread of human diseases, understanding the population dynamics and processes of taxa diversification is important for an effective mosquito control . Two vectors of West Nile virus, Cx. p. pipiens and Cx. p. molestus, exhibit epidemiologically important behavioral and physiological differences, but the whole-genome divergence between them was unexplored. The first goal of this study was to better understand the level of genomic differentiation and population structures of Cx. p. pipiens and Cx. p. molestus from different continents. We sequenced and compared whole genomes of 40 individual mosquitoes from two locations in Eurasia and two in North America. Principal Component, ADMIXTURE, and neighbor joining analyses of the nuclear genomes identified two major intercontinental, monophyletic clusters of Cx. p. pipiens and Cx. p. molestus. The level of genomic differentiation between the subspecies was uniform along chromosomes. The ADMIXTURE analysis determined signatures of admixture in Cx. p. pipens populations, but not in Cx. p. molestus populations. Thus, our study identified that Cx. p. molestus and Cx. p. pipiens represent different evolutionary units with monophyletic origin that have undergone incipient ecological speciation. The second goal was to study differences at the chromosome level between these two organisms. We first measured whole chromosome and chromosome arm length differences between Cx. p. molestus and Cx. p. pipiens as a basic cytogenetic approach. In addition, we used the novel Hi-C approach to detect chromosomal rearrangements between them since Hi-C was successful in detecting a known inversion in Cx. quinquefasciatus. Cx. p. molestus and Cx. p. pipiens embryos were used to perform the Hi-C technique. Analysis of the Hi-C data showed the presence of two different inversions in Cx. p. pipiens and Cx. p. molestus heatmap, which could explain their different physiology and adaptation in nature. Developing modern genomic and cytogenetic tools is important to enhance the quality of genome assemblies, improve gene annotation, and provide a better framework for comparative and population genomics of mosquitoes; also it is the foundation for the development of novel genome-based approaches for vector control. Doctor of Philosophy Mosquitoes are medically important insects because they vector a range of diseases that infect humans. The subfamily Culicinae is responsible for transmitting such diseases as Zika, dengue, and West Nile fevers, which have triggered fatal infections and epidemics in multiple parts of the world. Since 2010-2016, studies have reported exceeding levels of insecticide resistance that slows the disease elimination process. Novel transgenic techniques have a tremendous potential for more efficiently minimizing mosquito-borne diseases and transmission. Availability of high-quality genome assemblies for mosquitoes may help to better understand their population structure and to develop effective and safe vector-control approaches that we urgently need. For the development of high-quality genome assemblies, we need to construct a physical genome map, that shows the physical locations of genes or other DNA sequences of interest along the chromosomes. For this reason, we developed a new gene-based approach for the physical mapping of the mosquito genomes. This method was then used for the development of a physical map for Ae. albopictus. This study resulted in the generation of the first physical map of the Ae. albopictus genome. To understand population structure in Culicinae mosquitoes, we used mosquitoes from the Culex pipiens complex. Species in this complex transmit different arthropod-borne viruses or arboviruses. Notable is the West Nile Virus, which has triggered fatal infections and epidemics in Eastern and Central Europe, North America and is also known in Asia, Australia, Africa, and the Caribbean. We specifically focused on two subspecies in this complex, Cx. pipiens pipiens and Cx. pipiens molestus that are morphologically identical, but are different physiologically and behaviorally. Although they are spread globally in temperate regions, their population structure and taxonomic status remains unclear. The first goal of this study was to better understand the level of genomic differentiation of Cx. p. pipiens and Cx. p. molestus from different continents. We sequenced and compared the whole genomes of 40 individual mosquitoes from two locations in Eurasia and two in North America. Our study identified that Cx. p. molestus and Cx. p. pipiens represent different evolutionary units that are currently undergoing ecological speciation. The second goal was to study differences at the chromosome level between them. Using the Hi-C approach we detected presence of two different inversions in Cx. p. pipiens and Cx. p. molestus, which could potentially explain their different physiology and adaptation.

In the period from 2015 to 2020, an entomological survey for the presence of West Nile virus (WNV) and Usutu virus (USUV) in mosquitoes was performed in northwestern Croatia. A total of 20,363 mosquitoes were sampled in the City of Zagreb and Međimurje county, grouped in 899 pools and tested by real-time RT-PCR for WNV and USUV RNA. All pools were negative for WNV while one pool each from 2016 (Aedes albopictus), 2017 (Culex pipiens complex), 2018 (Cx. pipiens complex), and 2019 (Cx. pipiens complex), respectively, was positive for USUV. The 2018 and 2019 positive pools shared 99.31% nucleotide homology within the USUV NS5 gene and both clustered within USUV Europe 2 lineage. The next-generation sequencing of one mosquito pool (Cx. pipiens complex) collected in 2018 in Zagreb confirmed the presence of USUV and revealed several dsDNA and ssRNA viruses of insect, bacterial and mammalian origin.

Gynandromorphic insects bear both male and female characteristics. In mosquitoes, gynandromorphy has been documented in multiple species and it can include many different combinations of sex-specific traits such as plumose or filiform antennae, short or elongated palpi, and male or female terminalia. Here we report 4 gynandromorphic specimens of Culex erythrothorax, Cx. pipiens complex, Cx. tarsalis, and Culiseta incidens collected in the Northern San Joaquin Valley of California. Each of the specimens exhibited heads with female characteristics of short palpi and filiform antennae while displaying fully developed external male terminalia including basistyles and dististyles. The potential implication of gynandromorphism in genetic control of mosquito vectors is discussed.

In research into mosquitoes in the mountain regions of Croatia, a new species of mosquito for Croatian mosquito fauna has been identified. The Culex pipiens complex is represented with four sibling species. Culex torrentium belongs to this complex and morphologically differs from the other species only in the structure of male genitals. The presence of this species is determined based on the male genital structure and confirmed by mitochondrial cytochrome c oxidase molecular analysis. Specimens of these species have been found in all three mountain areas covered by this research: Slavonian mountains, Gorski Kotar area and central Velebit Mt. The lowest altitude where we found this species was 159 metres above sea level (m a.s.l.) in Pleternica, and the highest 906 m a.s.l. in Baške Oštarije. At all sites, the species Cx. torrentium was sampled in community with other species, but most frequently together with sibling species of Cx. pipiens (most probably the subspecies Cx. p. pipiens).

In Europe, West Nile virus (WNV) outbreaks have been limited to southern and central European countries. However, competent mosquito vectors and susceptible bird hosts are present in northern Europe. Differences in temperature and vector competence of mosquito populations may explain the absence of WNV outbreaks in northern Europe. The aim of the present study was to directly compare vector competence of northern and southern European Culex pipiens (Cx. p.) pipiens mosquitoes for WNV across a gradient of temperatures. WNV infection and transmission rates were determined for two Cx. p. pipiens populations originating from The Netherlands and Italy, respectively. Mosquitoes were orally exposed by providing an infectious bloodmeal, or by injecting WNV (lineage 2) in the thorax, followed by 14-day incubation at 18, 23, or 28 °C. No differences in infection or transmission rates were found between the Cx. p. pipiens populations with both infection methods, but WNV transmission rates were significantly higher at temperatures above 18 °C. The absence of WNV outbreaks in northern Europe cannot be explained by differences in vector competence between Cx. p. pipiens populations originating from northern and southern Europe. This study suggests that low temperature is a key limiting factor for WNV transmission.

The area in and around Chicago, IL, is a hotspot of West Nile virus activity. The discovery of a Culex pipiens form molestus Forskӓl population in Chicago in 2009 added to speculation that offspring from hybridization between Cx. pipiens f. pipiens L. and f. molestus could show a preference for feeding on humans. We collected blood-fed female mosquitoes (N = 1,023) from eight residential sites and one public park site in Chicago in July and August 2012. Bloodmeal analysis using the COI (cytochrome c oxidase subunit I) gene was performed to ascertain host choice. Almost all (99%) bloodmeals came from birds, with American Robins (Turdus migratorius L.) and House Sparrows (Passer domesticus L.) making up the largest percentage (74% combined). A forage ratio analysis comparing bird species fed upon and available bird species based on point count surveys indicated Northern Cardinals (Cardinalis cardinalis) and American Robins (Turdus migratorius) appeared to be over-utilized, whereas several species were under-utilized. Two human bloodmeals came from Culex pipiens complex mosquitoes. Admixture and population genetic analyses were conducted with 15 microsatellite loci on head and thorax DNA from the collected blood-fed mosquitoes. A modest amount of hybridization was detected between Cx. pipiens f. pipiens and f. molestus, as well as between f. pipiens and Cx. quinquefasciatus Say. Several pure Cx. quinquefasciatus individuals were noted at the two Trumbull Park sites. Our data suggest that Cx. pipiens complex mosquitoes in the Chicago area are not highly introgressed with f. molestus and appear to utilize avian hosts.

WOS: 000455617600001 Mosquitoes are one of the organisms subjected to frequent insecticide application due to their status as vectors that carry a wide range of life-threatening diseases. Turkey has climatic and other ecological features required for the breeding and living of 50 species from 8 genera. The members of the Culex pipiens complex are the dominant mosquitoes among them. In order to design more sustainable insecticide resistance management strategies, it is important to investigate the genetic structure of mosquito populations using molecular techniques. The aim of this study was the genetic characterization of field populations of C. pipiens sampled from 25 different sublocations belonging to 6 provinces in the Aegean region of Turkey by using random amplified polymorphic DNA (RAPD) markers. Eighty 10-mer RAPD primers were screened on a subset of DNAs. Among them, 20 reproducible and clear band-producing polymorphic primers were selected and applied to all study material. A low level of genetic differentiation and a high level of gene flow were detected between the populations. Scientific and Technological Research Council of Turkey (TUBITAK-KBAG)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [111T387]; Mugla Sitki Kocman University Scientific Research FundsMugla Sitki Kocman University [MUBAP-2012/71] As part of a comprehensive project, this study was financially supported by the Scientific and Technological Research Council of Turkey (TUBITAK-KBAG), project number 111T387, and the Mugla Sitki Kocman University Scientific Research Funds, project number MUBAP-2012/71.

The Culex pipiens complex includes species with reported differences in vector competence for arthropod-borne viruses, many of which are of significant importance to human health such as the West Nile virus and the Sindbis virus. This group of mosquitoes is difficult to distinguish morphologically; particularly as adult females. In Europe, the two species of the complex, Culex pipiens Linnaeus 1758 and Culex torrentium Martini 1925, are often found sympatrically. With the aim to characterize the presence and spread of both species in the Emilia-Romagna region, Northern Italy, mosquitoes of the complex - collected during the West Nile virus surveillance plans - were tested by multiplex real-time PCR for the detection of the two species Cx. pipiens and Cx. torrentium. A total of 24 165 mosquitoes, collected between 2012 and 2014 from 105 sites, and sorted in 204 pools, were tested. All tested pools were found to be composed of Cx. pipiens, whereas Cx. torrentium was not detected. These results indicate a likely absence of Cx. torrentium mosquitoes within the surveyed territory, whereas Cx. pipiens is widely distributed in the area mentioned. This is in line with previous reports, which describe a pre-alpine distribution of Cx. torrentium in Italy.

Background Despite long-term research on dirofilariosis in Slovakia, little attention has thus far been paid to Dirofilaria vectors. The particular aim of the present study was molecular screening for filarioid parasites in two different habitats of Bratislava, the capital city of Slovakia. In addition, the effect of urbanisation on mosquito species abundance and composition, associated with the risk of mosquito-borne infections, was studied and discussed. Methods Mosquitoes were identified by morphological features, and molecular methods were also used for determination of selected individuals belonging to cryptic species from the Anopheles maculipennis and Culex pipiens complexes. The presence of filarioid DNA (Dirofilaria repens, Dirofilaria immitis and Setaria spp.) was detected using standard PCR approaches and sequencing. Results A total of 6957 female mosquitoes were collected for the study. Overall, the most abundant mosquito species was Aedes vexans, closely followed by unidentified members of the Cx. pipiens complex and the less numerous but still plentiful Ochlerotatus sticticus species. Further investigation of mosquito material revealed 4.26% relative prevalence of Dirofilaria spp., whereby both species, D. repens and D. immitis, were identified. The majority of positive mosquito pools had their origin in a floodplain area on the outskirts of the city, with a relative prevalence of 5.32%; only two mosquito pools (1.26%) were shown to be positive in the residential zone of Bratislava. Setaria spp. DNA was not detected in mosquitoes within this study. Conclusions The study presented herein represents initial research focused on molecular mosquito screening for filarioid parasites in urban and urban-fringe habitats of Bratislava, Slovakia. Molecular analyses within the Cx. pipiens complex identified two biotypes: Cx. pipiens biotype pipiens and Cx. pipiens biotype molestus. To our knowledge, Dirofilaria spp. were detected for the first time in Slovakia in mosquitoes other than Ae. vexans, i.e. D. repens in Anopheles messeae and unidentified members of An. maculipennis and Cx. pipiens complexes, and D. immitis in Coquillettidia richiardii and Cx. pipiens biotype pipiens. Both dirofilarial species were found in Och. sticticus. The suitable conditions for the vectors’ biology would represent the main risk factor for dirofilariosis transmission.

Mosquitoes in the Culex pipiens complex (Diptera: Culicidae), especially Cx. pipiens and Culex quinquefasciatus, have successfully exploited the rapid growth of the human population and globalization to their advantage by successfully utilizing man-made habitats, particularly for oviposition. Culex spp. lay over 100 eggs together in a raft. Each egg in the raft produces an apical droplet containing an oviposition attractant, erythro-6-acetoxy-5-hexadecanolide, commonly referred to as Mosquito Oviposition Pheromone (MOP). Here we present a detailed gas chromatography–mass spectrometry (GC–MS) analysis of the apical droplets from six populations that revealed MOP as the most abundant constituent. Subjecting MOP and the remaining 17 most abundant chemical constituents of the droplets from these populations to a Principal Component Analysis (PCA) resolved the populations into two distinct clusters that contained two populations each of Cx. quinquefasciatus and Culex pipiens molestus. The two Culex pipiens pipiens, however, did not resolve into a single cluster, with the Shasta population sorting closer to Cx. quinquefasciatus. Comparing the PCA scores with the genetic evidence from adult females using available molecular markers that have earlier shown to sort various Culex forms, we found that the molecular data support the PCA clustering pattern. Behavioral investigation of the droplet-induced attraction tested in gravid Cx. quinquefasciatus elicited various degrees of oviposition to the droplets from each population. Overall, droplets from all six populations induced higher attraction compared to controls. A detailed time-course analysis of droplet composition in Cx. quinquefasciatus from 6 to 54 h post egg-laying identified MOP again as the main constituent. Finally, our electrophysiological investigation identified MOP as the only biologically active constituent from of the droplets eliciting responses from female antennae. These studies will aid in global efforts to understand the vector biology and evolution that can be exploited to develop novel vector management strategies.

Mosquito surveillance was conducted in 42 underground parking lots in the densely populated metropolitan area of Wuhan, Hubei Province, central China from Aug to Oct 2012. Autogenous Culex p. molestus mosquitoes, which inhabit underground sites elsewhere in China, were identified and recorded for the first time in Hubei Province. Also Culex quinquefasciatus and intermediates (presumably with Cx. p. pallens) were identified from the samples, but Cx. p. pallens, which is known to hybridize with Cx. quinquefasciatus, was not found during the study. We attempted to determine how to differentiate between the subspecies of the Culex pipiens complex in Wuhan. In the female wings of Cx. p molestus, the subcosta intersected the costa beyond or at the furcation of R2+3; however in Cx. quinquefasciatus and intermediates, the subcosta intersected the costa before the furcation of R2+3. In female abdomens of Cx. p. molestus, lateral patches on tergum II reached the posterior margins; however in Cx. quinquefas...

Microsatellite markers were used to genetically characterize 19 Culex pipiens complex populations from California. Two populations showed characteristics of earlier genetic bottlenecks. The overall FST value and a neighbor-joining tree suggested moderate amounts of genetic differentiation. Analyses using Structure indicated K = 4 genetic clusters: Cx. pipiens form pipiens L., Cx. quinquefasciatus Say, Cx. pipiens form molestus Forskäl, and a group of genetically similar individuals of hybrid origin. A Discriminant Analysis of Principal Components indicated that the latter group is a mixture of the other three taxa, with form pipiens and form molestus contributing somewhat more ancestry than Cx. quinquefasciatus. Characterization of 56 morphologically autogenous individuals classified most as Cx. pipiens form molestus, and none as Cx. pipiens form pipiens or Cx. quinquefasciatus. Comparison of California microsatellite data with those of Cx. pipiens pallens Coquillett from Japan indicated the latter does not contribute significantly to genotypes in California.

Recent reports of Zika virus (ZIKV) isolates from Culex species mosquitoes have resulted in concern regarding a lack of knowledge on the number of competent vector species for ZIKV transmission in the new world. Although observations in the field have demonstrated that ZIKV isolation can be made from Culex species mosquitoes, the detection of ZIKV in these mosquitoes is not proof of their involvement in a ZIKV transmission cycle. Detection may be due to recent feeding on a viremic vertebrate, and is not indicative of replication in the mosquito. In this study, susceptibility of recently colonized Culex species mosquitoes was investigated. The results showed a high degree of refractoriness among members of Culex pipiens complex to ZIKV even when exposed to high-titer bloodmeals. Our finding suggests that the likelihood of Culex species mosquitoes serving as secondary vectors for ZIKV is very low, therefore vector control strategies for ZIKV should remain focused on Aedes species mosquitoes. Our demonstration that Culex quinquefasciatus from Vero Beach, FL, is refractory to infection with ZIKV is especially important and timely. Based on our data, we would conclude that the autochthonous cases of Zika in Florida are not due to transmission by C. quinquefasciatus, and so control efforts should focus on other species, logically Aedes aegypti and Aedes albopictus.

Members of the Culex pipiens complex have been implicated as vectors of a number of arboviruses including St. Louis encephalitis, West Nile, Sindbis, and Rift Valley fever viruses. For some viruses, such as West Nile virus, laboratory studies have indicated that various members of this complex have a similar ability to become infected with and transmit virus, thus providing evidence for the similarity among the various members of this complex. On the other hand, although strains of Cx. pipiens from various parts of the world have all been relatively efficient vectors of Rift Valley fever virus, Cx. quinquefasciatus from Africa, Australia, and North America have been nearly refractory to this virus, thus indicating that the various members of this complex do not necessarily respond similarly to a particular arbovirus. Based on the similar response to some viruses and differing response to others, Cx. pipiens and Cx. quinquefasciatus appear to be closely related, but distinct species.

West Nile virus (WNV) is now endemic in California, with annual transmission documented by the statewide surveillance system. Although much is known about the horizontal avian-mosquito transmission cycle, less is known about vertical transmission under field conditions, which may supplement virus amplification during summer and provide a mechanism to infect overwintering female mosquitoes during fall. The current study identified clusters of WNV-infected mosquitoes in Sacramento and Yolo Counties, CA, during late summer 2011 and tested field-captured ovipositing female mosquitoes and their progeny for WNV RNA to estimate the frequency of vertical transmission. Space-time clustering of WNV-positive Culex pipiens complex pools was detected in the northern Elk Grove area of Sacramento County between July 18 and September 18, 2011 (5.22 km radius; p0.001 and RR=7.80). Vertical transmission by WNV-infected females to egg rafts was 50% and to larvae was 40%. The estimated minimal filial infection rate from WNV-positive, ovipositing females was 2.0 infected females/1,000. The potential contribution of vertical transmission to WNV maintenance and amplification are discussed.

Cu l ex pi nsa is am eb r of th C . c pl x nJ . ecological conditions favorable for overwintering of Cx. p. pallens in urban areas are un-known. In two culverts of an urban environment in Saitama Prefecture, we collected 163 and 65 overwintering Culex adult mosquitoes in February 2005, and 133 and 51 in early March 2006, respectively. Molecular identi cation of 89 mosquitoes collected from culvert A in 2005 showed that all specimens were Cx. p. pallens . Our nding shows that the overwinter-ing sites of Cx. p. pallens in an urban environment. It is important to understand the ecology of overwintering of Cx. p. pallens in an urban areas and consequently contribute to control of overwintering mosquitoes.Key words: Culex pipiens pallens , overwintering site, urban environment, culvert I ˜ ˇ˜ Members of the Culex pipiens complex are potential vectors of human lymphatic laria-sis, dog heart worm and various viruses caus-ing encephalitis such as St. Louis encephalitis, equine encephalitis and West Nile fever. In the United States, a West Nile fever epidemic has been ongoing since 1999, and patients have exceeded 30,000, with more than 1,200 fatalities in the last 11 years (CDC, 2011). West Nile virus (WNV) is maintained in na-ture by many species of birds as amplifying hosts, and the virus has been detected in more than 326 species of birds in the United States, although there are great di erences in the viremia level among bird species (CDC, 2009; Wheeler et al., 2009). WNV has also been detected in 64 mosquito species, includ-ing genera

A granular formulation of 1.0% temephos (temephos G) was tested for its efficacy in mosquito larval control, residual effects and effects on non-target microorganisms. Culex pipiens complex in septic tanks in Yangsan, Republic of Korea were used for this study. Microorganisms in the same septic tanks were used for study of non-target organisms. After the application of temephos G at the rates of 2.0 and 5.0 mg/L to selected septic tanks, mortalities were recorded for 50 days. The effect of temephos G on non-target organisms was studied by evaluating its effects on the bacterial populations in the treated septic tanks. It was observed that using 1.0% temephos G at a rate of 2.0 mg/L resulted in 100% mortality against Cx. pipiens larvae by the eighth day after treatment. The residual activity of temephos G was observed to continue for a time; for example 29 days after treatment, average larval mortality rates of >68.0% were observed for both concentrations. At the 50th day after treatment, the mortality rates of the Cx. pipiens larvae were observed to decrease to below 42.7% for both concentrations. Application of temephos G did not have significant effects on the bacteria populations in the septic tanks. Since temephos did not seem to have any major effects on the microorganisms, it was concluded that it is a safe and effective larvicide to use in the septic tanks at a rate of 2.0-5.0 mg/L of 1.0% temephos G.

Objective To determine the variations in morphological characters of Culex pipiens complex and identify the species complex. Methods A study was carried out from April to October 2009 in Yazd Province, Iran. This study was performed in two randomly selected rural villages in Yazd County using different sampling methods such as larval collection, hand catch, pyrethrum space spray, light trap, and pit shelter collections. The data were analyzed using SPSS software Ver. 16. ANOVA and Tukey's post-hoc test was used to compare the ratios of the samples. Results The average of the DV/D ration was 0.090±0.007 and the range was 0-0.33. The average D/V ratio was 1.07±0.02, with maximum 1.6 and minimum 0.6. The costa and subcosta intersection were observed beyond the bifurcation of R2+3 in most of the specimens. The bifurcations of R2+3 and M1+3 veins were not on one direction in all samples. The range of the R-Cell/R2+3 ratio was 2.42-7.91. The average ratio of cross wing was 2.25±0.04 with a range of 1.36-3.70. Conclusions More populations of Culex pipiens from different areas of Iran need to be studied to gain complete information about the taxonomy and ecology of the species.

Variation among natural populations of Culex (Culex) quinquefasciatus Say is associated with different vectorial capacities. The species Cx. quinquefasciatus is present in the equatorial, tropical and subtropical zones in the Brazilian territory, with intermediate forms between Cx. quinquefasciatus and Culex pipiens occurring in regions of latitudes around 33°-35° S. Herein, we studied geographically distinct populations of Cx. quinquefasciatus by genetic characterization and analysis of intra-specific wing morphometrics. After morphological analysis, molecular characterization of Cx. quinquefasciatus and intermediate forms was performed by polymerase chain reaction of the polymorphic nuclear region of the second intron of the acetylcholinesterase locus. Additionally, the morphology of adult female wings collected from six locations was analyzed. Wing centroid sizes were significantly different between some geographical pairs. Mean values of R2/R2+3 differed significantly after pairwise comparisons. The overall wing shape represented by morphometric characters could be divided into two main groupings. Our data suggest that Brazilian samples are morphologically and genetically distinct from the Argentinean samples and also indicated a morphological distinction between northern and southern populations of Brazilian Cx. quinquefasciatus. We suggest that wing morphology may be used for preliminary assessment of population structure of Cx. quinquefasciatusin Brazil.

The variability of 13 larval morphological characteristics in the urban mosquito, Culex pipiens f. molestus and Culex torrentium, was investigated. These species, belonging to the Culex pipiens complex, are characterized by rapid ecological and evolutionary processes following the human-induced environmental changes. A comparison of 4 geographical larval populations of C. pipiens f. molestus and Culex torrentium revealed different rates of divergence of different morphological traits. In the older form in terms of evolutionary development, C. torrentium, the two local populations differed in the structures of the trophic morphological complex characterized by a higher functional trophic load, while the structures with a lower functional load did not differ between the populations. On the contrary, the populations of the younger form, C. pipiens f. molestus, which had recently colonized new urban sites, differed in the structures with a low functional trophic load (some structures of siphon and abdominal segment IX), whereas structures of the trophic morphological complex were similar in different populations. The possible mechanisms of these morphological transformations and their role in the evolution of mosquito larvae are discussed.

The identification of the members of the Culex pipiens L. complex in arbovirus surveillance programs relies heavily on the use of morphology. In this work, we studied Cx. pipiens complex male mosquitoes collected from nine different locations, from northern, southern, and the hybrid zone sites in North America; Cairo, Egypt; and Nairobi, Kenya. Specimens were identified using DV/D ratio and also using amplification of the acetylcholinesterase (ACE.2) gene by both conventional and real-time polymerase chain reaction, and examination of the CQ11 locus. Consistent with previous findings, the morphological and molecular identifications did not always agree, particularly in regions of extensive introgression. There was an increased frequency of hybrid forms in late summer and early fall in Champaign Co., IL, that is north of the previously described Cx. pipiens complex hybrid zone. This represents an expansion of the North American hybrid zone. The biological and epidemiological relevance of the high degree of introgression and the late season increase in the proportion of intermediate forms is discussed.

A previously developed method to identify members of the Culex pipiens complex exploiting polymorphisms in a nuclear intron (acetylcholinesterase [ACE] based-assay) cannot differentiate the two forms of Cx. pipiens: form pipiens and form molestus. Notably, the two forms seem to differ extensively in behavior and physiology and likely have very different epidemiologic importance. Because they are morphologically indistinguishable, molecular methods are critical for the evaluation of their relative importance. Although the two forms of Cx. pipiens have been distinguished using a panel of microsatellite loci, such a protocol is laborious and expensive. We developed a rapid assay based on polymorphisms in the flanking region of a microsatellite locus. Used in conjunction with the ACE-assay, this new assay allows the identification of pure and hybrid populations of the two Cx. pipiens forms as well as those including Cx. quinquefasciatus. We discuss the usefulness of the method as well as limitations to its application.

Members of the Culex pipiens complex are principal vectors for West Nile virus (WNV) in the USA. Previous studies have shown that gravid traps might be more effective than CO2-baited traps in sampling for Cx. pipiens. We compared the efficacy of gravid traps manufactured by 3 different companies: Bioquip, Clarke, and J. W. Hock. All gravid traps have a similar setup to hold the oviposition attractant but differ in the way they collect the mosquitoes. The gravid trap manufactured by J. W. Hock Company trapped significantly more Cx. pipiens than the other traps. Because CO2-baited American Biophysics Corporation (ABC) traps are most often used by mosquito abatement agencies, we compared the efficacy of the Hock gravid trap with a CO2-baited ABC trap. There was no significant difference in the number of Cx. pipiens trapped between the Hock gravid and CO2-baited ABC trap. Because gravid traps predominantly attract previously bloodfed females (thereby aiding in WNV surveillance) and are logistically easier and cheaper to set up, we argue that the Hock gravid trap might be ideal for sampling Cx. pipiens populations.

We investigated mosquito sampling techniques with two types of traps and attractants at different time for trapping potential vectors for Rift Valley Fever virus. The study was conducted in six villages in Ngorongoro district in Tanzania from September to October 2012. A total of 1814 mosquitoes were collected, of which 738 were collected by CDC light traps and 1076 by Mosquito Magnet trapping technique. Of the collected mosquitoes, 12.46% (N = 226) were Aedes aegypti and 87.54% (N = 1588) were Culex pipiens complex. More mosquitoes were collected outdoors using Mosquito Magnets baited with octenol attractant, 36.38% (N =660) followed by indoor trapping using CDC light traps without attractant, 29.60% (N = 537). Most of Ae. aegypti mosquitoes were collected outdoor using Mosquito Magnets, 95% (N = 214) whereas Cx. pipiens complex were trapped both indoor using CDC light traps without attractant and outdoors using both CDC light traps baited with carbon dioxide (CO2) sachets and Mosquito Magnets. Analysis on the differences in abundance of mosquitoes trapped by different techniques using Generalized Linear Models was statistically significance at p-value < 0.05 for both species. Three hours mosquito collections show differing patterns in activity, most Ae. aegypti species were collected primarily during the first and last quarters of the day. Cx pipiens complex was active throughout the night, early evening and early morning then decreased markedly during the day time. The results presented in this paper emphasize the possibility of using Mosquito Magnets in order to efficiently capture these potential RVF vectors.

Background Culex pipiens L. complex mosquitoes have a global distribution and are primary vectors of pathogens of public health significance. In the U.S., Cx. pipiens bioformes, Cx. pipiens form pipiens and Cx. pipiens form molestus, as well as Cx. quinquefasciatus, are primary vectors of West Nile virus (WNV; Flaviviridae, Flavivirus). These mosquitoes reside in distinct but overlapping ecological niches and readily hybridize in areas where they coexist. Although species and population-specific differences in vector competence of Culex mosquitoes for WNV have been identified, the extent to which hybridization within this complex alters WNV transmission potential has not been well characterized. Findings WNV vector competence of laboratory colonies of Cx. p. f. pipiens, Cx. p. f. molestus, and Cx. quinquefasciatus was assessed and compared to hybrid populations created from reciprocal mating of these lines. The results demonstrate that hybridization has a significant effect on WNV infection, dissemination, and, particularly, transmission in Culex pipiens L. complex mosquitoes. Specifically, enhanced transmission of WNV was measured in all hybrid populations relative to one or both parental stains. Conclusion These findings demonstrate that environmental or anthropogenic changes resulting in fluctuations in the distribution and extent of hybrid populations of Culex mosquitoes could have a significant impact on transmission patterns of WNV in nature.

Members of the Culex pipiens complex are the primary vectors of St. Louis encephalitis virus and West Nile virus in the Mississippi River basin (MRB). The Cx. pipiens complex in the MRB is composed of 4 taxa: Cx. p. pipiens form pipiens, Cx. p. quinquefasciatus, hybrids between Cx. p. pipiens f. pipiens and Cx. p. quinquefasciatus, and Cx. p. pipiens form molestus. Three studies on bloodmeal hosts with large sample sizes have been conducted on members of the Cx. pipiens complex in the MRB including 1 each on Cx. p. quinquefasciatus from Louisiana, Cx. p. pipiens-quinquefasciatus hybrids from Tennessee, and Cx. p. pipiens from Illinois. The top 8 bloodmeal hosts from each of the 3 sites accounted for 68-92% of bloodmeals. Only 14 species accounted for the top 8 bloodmeal hosts at each of the 3 sites. The most often utilized bloodmeal hosts for members of the Culex pipiens complex within the MRB are the American robin, Northern cardinal, human, raccoon, common grackle, house sparrow, mourning dove, dog, Northern mockingbird, blue jay, opossum, domestic horse, house finch and European starling. Human feeding varied widely among sites from 1% to 15.7% of bloodmeals. The proportion of bloodmeals taken on humans is an important epidemiological variable and future studies are needed to define the primary genetic and environmental factors that influence host utilization by members of the Cx. pipiens complex.

Studies on the vector-host interactions of Culex pipiens complex mosquitoes by sequencing portions of mitochondrial cytochrome b gene indicate that Cx. p. pipiens f. pipiens predominantly feed on avian hosts (93.1%), and focus feeding activity on several key bird species, in particular the American robin, the gray catbird, and the house sparrow in Connecticut. However, Cx. p. quinquefasciatus indiscriminately feed on both birds and mammals. Culex p. quinquefasciatus in Harris County - Texas and southern California acquired 39.1% and 88.2% of bloodmeals from birds, respectively. Mammalian-derived bloodmeals constituted 52.5% and 9.6% in the two regions, respectively. The most frequent avian hosts for this mosquito species in the southwestern U.S. were the mourning dove, the white-winged dove, the house sparrow and the house finch. Humans infrequently served as the source of bloodmeals for Cx. p. pipiens and Cx. p. quinquefasciatus. Microsatellite analysis of mosquitoes from Chicago, Illinois showed that Cx. p. pipiens f. pipiens with mammalian- derived bloodmeals had significantly higher ancestry and proportion of hybrids from Cx. p. pipiens f. molestus than did those with avian-derived bloodmeals.

Pulsed-field gel electrophoresis analysis of Beijing and Californian populations of Culex pipiens complex mosquitoes revealed that the enzyme Mlul produced a band of 49kb. This probably is one whole amplification unit, the largest fragment found so far in the mosquitoes. The method for the preparation of large DNA molecules was described and the electrophoretic condition for the separation of large DNA molecules is discussed.

The Report “Emerging vectors in the Culex pipiens complex” by D. M. Fonseca et al. (5 Mar., p. [1535][1]) advances sweeping extrapolations concerning mosquito blood-feeding behavior and West Nile virus (WNV) transmission. These findings led Fonseca to conclude ([1][2]) that a European

The present paper is the results of the biosystematic studies of Culex pipiens complex in China, including hybridization, mathematical analyses of morphological characters and GC analyses of culticular hydrocarbons. On the bases of the results of these studies, in addition to their allopatric distribution, it can be concluded that Cx. pipiens complex in China consists of four subspecies, including Cx. p ipiens molestus recently discovered in Beijing. Cx. pipiens quinquefasciatus can not be considered as a spearate species and Cx. pipiens pallens is not an intermediate form as claimed by some western workers.

Mosquitoes belonging to the Culex pipiens complex are primary vectors for diseases such as West Nile encephalitis, Eastern equine encephalitis, many arboviruses, as well as lymphatic filariases. Despite sharing physiological characteristics, each mosquito species within the Culex complex has unique behavioural and reproductive traits that necessitate a proper method of identification. Unfortunately, morphometric methods of distinguishing members of this complex have failed to yield consistent results, giving rise to the need for molecular methods of identification. In this study, we propose a novel identification method using high-resolution melting (HRM) analysis by examining single-nucleotide polymorphisms in the acetylcholinesterase-2 (ace-2) locus. Our method provides a high confidence for species determination among the three Culex complex mosquitoes.

Background Analysis of Culex pipiens mosquitoes collected from a single site in Lebanon in 2005, revealed an alarming frequency of ace-1 alleles conferring resistance to organophosphate insecticides. Following this, in 2006 the majority of municipalities switched to pyrethroids after a long history of organophosphate usage in the country; however, since then no studies have assessed the impact of changing insecticide class on the frequency of resistant ace-1 alleles in C. pipiens. Methods C. pipiens mosquitoes were captured indoors from 25 villages across the country and subjected to established methods for the analysis of gene amplification at the Ester locus and target site mutations in ace-1 gene that confer resistance to organophosphates. Results We conducted the first large-scale screen for resistance to organosphosphates in C. pipiens mosquitoes collected from Lebanon. The frequency of carboxylesterase (Ester) and ace-1 alleles conferring resistance to organophosphates were assessed among C. pipiens mosquitoes collected from 25 different villages across the country between December 2008 and December 2009. Established enzymatic assay and PCR-based molecular tests, both diagnostic of the major target site mutations in ace-1 revealed the absence of the F290V mutation among sampled mosquitoes and significant reduction in the frequency of G119S mutation compared to that previously reported for mosquitoes collected from Beirut in 2005. We also identified a new duplicated ace-1 allele, named ace-1D13, exhibiting a resistant phenotype by associating a susceptible and a resistant copy of ace-1 in a mosquito line sampled from Beirut in 2005. Fisher’s exact test on ace-1 frequencies in the new sample sites, showed that some populations exhibited a significant excess of heterozygotes, suggesting that the duplicated allele is still present. Starch gel electrophoresis indicated that resistance at the Ester locus was mainly attributed to the Ester2 allele, which exhibits a broad geographical distribution. Conclusions Our analysis suggests that the frequency of resistant ace-1 alleles in mosquito populations can be downshifted, and in certain cases (F290V mutation) even eliminated, by switching to a different class of insecticides, possibly because of the fitness cost associated with these alleles.

Culex pipiens complex mosquitoes are widely distributed throughout China and are known to be important disease vectors. Two pyrethroid resistance associated mutations have been identified in Cx. pipiens complex (Diptera: Culicidae), but there is little information on the diversity and distribution of kdr alleles in pyrethroid resistance in Cx. pipiens complex mosquitoes in China. In the present study, we report on a modified three tube allele-specific (AS)-PCR method for detecting the 1014F and 1014S alleles. The new technique was applied to identify the distribution of the two alleles in natural Cx. pipiens complex populations in China. The results confirmed that the new method is both sensitive and specific. The 1014F allele was found in all 14 of the field populations tested (frequency ranged from 6.8 to 76.2%) and the 1014S allele was found in almost two-thirds (frequency from 2.4 to 28.6%), indicating that the genotypes known to be associated with pyrethroid resistance are widespread in China. The resistance-associated alleles were more common in southern Chinese sampling sites than in northern sites. The coexistence of the two resistant mutations in individual mosquitoes was also observed in five of the field populations. Two alternative mutations within the L1014 codon were identified in Culex pipiens molestus Forskal, 1775, including a non-synonymous mutation resulting in a 1014C substitution.

Background: Culex pipiens complex shows variations in morphological and biological characters including different biological forms and has medical and veterinary importance. Because of having morphological variations, sometimes it is not easy to separate this species from Cx. quinquefasciatus and Cx. torrentium. The aim of this study was to identify the Culex pipiens complex species in order to use in control programs in the future. Methods: This study was carried out in two randomly selected rural villages in Yazd County, eastern Iran using dipping technique from April to October 2009. The data were analyzed using SPSS software version 16. Results: Average of siphon index in fourth-instrar larvae was 3.86±0.03, the minimum and maximum were calculated 2.43 and 5.14, respectively. Siphon/Saddle index was measured as average, minimum and maximum 3.2±0.2, 2.78, and 4.42 respectively. In our study, only 4 specimens had single seta 1 on segments III and VI (2.5%) and the remaining beard double seta (97.5%). The maximum 3–6 branches seta 1a-S and 1b-S (95%) were observed on siphon. Conclusion: More populations of Culex pipiens from different areas of Iran need to be studied to gain complete information about the taxonomy and ecology of the species in the country.

Multiple assays are available to measure P450 activity in insects, including mosquitoes; however, each of these assays has drawbacks in terms of the number of mosquitoes required, specificity, sensitivity, cost, and/or time required to prepare active enzyme homogenates. In this study, a commercially available luminescent assay, P450-Glo, was modified and evaluated to measure P450 activity from the gut of a single larva after removal of the gut contents. We also compared this assay to an earlier developed fluorescent assay. After optimization of assay conditions, the P450-Glo assay held considerable promise to be used as an effective, inexpensive, high-throughput, and sensitive screening assay to measure P450 activities in single mosquitoes. Furthermore, we tested the utility of the single gut assay using the pyrethroid resistant Marin strain of Culex pipiens pipiens form molestus and the pyrethroid sensitive CQ-1 strain of Cx. pipiens quinqefasciatus. We observed on average 1.8-fold higher levels of P450 activity in the resistant mosquitoes in comparison to the sensitive mosquitoes. Additionally, consistent with our previous findings, distribution plots of P450 activity showed 33% of individual Marin mosquitoes had higher P450 activities than the highest activity displayed by a CQ-1 mosquito. The assay platform is highly flexible in terms of choice of tissue, method of preparation, isozyme specificity, and sample quantity and thus could easily be adapted to be used for other arthropod species.

We evaluated the susceptibility to infection and transmission of West Nile virus (WNV) in seven populations of Culex pipiens pipiens (L.), Cx. p. quinquefasciatus Say, and from populations containing Cx. pipiens/quinquefasciatus hybrids in a north-south transect of California. Samples were identified to species or as hybrid forms based on morphology of male terminalia. After 7 and 14 days of extrinsic incubation, few females were infected and none transmitted WNV from samples of Cx. p. pipiens from northern Shasta County and of Cx. p. quinquefasciatus from southern Los Angeles County. Seven days after infective feeding, 13%-36% of mosquitoes from the counties of Merced, Fresno, Kern, and San Bernardino were infected, and 12%-40% of infected mosquitoes expressed WNV in salivary expectorate. Fourteen days after infective feeding, 18%-43% of mosquitoes from these counties were infected, and 50%-69% of infected mosquitoes transmitted WNV in salivary expectorate. A sample of Cx. p. quinquefasciatus from Riverside County did not transmit WNV after 7 days, but 71% transmitted 14 days after infective feeding. These results reveal extensive geographic variation in vector competence for WNV in the Culex pipiens complex in California.

Culex pipiens, an invasive mosquito and vector of West Nile virus in the US, has two morphologically indistinguishable forms that differ dramatically in behavior and physiology. Cx. pipiens form pipiens is primarily a bird-feeding temperate mosquito, while the sub-tropical Cx. pipiens form molestus thrives in sewers and feeds on mammals. Because the feral form can diapause during the cold winters but the domestic form cannot, the two Cx. pipiens forms are allopatric in northern Europe and, although viable, hybrids are rare. Cx. pipiens form molestus has spread across all inhabited continents and hybrids of the two forms are common in the US. Here we elucidate the genes and gene families with the greatest divergence rates between these phenotypically diverged mosquito populations, and discuss them in light of their potential biological and ecological effects. After generating and assembling novel transcriptome data for each population, we performed pairwise tests for nonsynonymous divergence (Ka) of homologous coding sequences and examined gene ontology terms that were statistically over-represented in those sequences with the greatest divergence rates. We identified genes involved in digestion (serine endopeptidases), innate immunity (fibrinogens and α-macroglobulins), hemostasis (D7 salivary proteins), olfaction (odorant binding proteins) and chitin binding (peritrophic matrix proteins). By examining molecular divergence between closely related yet phenotypically divergent forms of the same species, our results provide insights into the identity of rapidly-evolving genes between incipient species. Additionally, we found that families of signal transducers, ATP synthases and transcription regulators remained identical at the amino acid level, thus constituting conserved components of the Cx. pipiens proteome. We provide a reference with which to gauge the divergence reported in this analysis by performing a comparison of transcriptome sequences from conspecific (yet allopatric) populations of another member of the Cx. pipiens complex, Cx. quinquefasciatus.

Several strains of Bacillus sphaericus (Neide) (Bsph), a spore-forming bacterium that produces potent mosquitocidal toxins, have been widely used against mosquito larvae globally. In some locations in the field and in the laboratory, moderate to high levels of resistance in Culex pipiens complex mosquito larvae to Bsph have been reported. Practical strategies for dealing with the resistance problem and more importantly to delay or possibly prevent development of resistance to Bsph in the first place are urgently needed. From published reports, we deduced that Bsph-resistant mosquito larvae are completely susceptible to Bacillus thuringiensis ssp. isreaelensis (Bti) and that there is no appearance of cross-resistance to Bti. On the basis of this information, we hypothesized that Bti offers a good potential for the management of resistance to Bsph, especially when it comes to delaying or preventing emergence of resistance. We conducted laboratory studies to see whether rotation of Bsph and Bti or mixture of both delays or prevents resistance development in Bsph-susceptible California Cx. quinquefasciatus. Development of resistance using Bsph alone increased after F15 and fluctuated slightly on further selections. Rotation of Bsph and Bti resulted in much higher level and rapid emergence of resistance to Bsph. However, selection with mixtures of Bti and Bsph for 36 generations showed no emergence of resistance. On the basis of this information, we believe mixtures have a good potential in delaying or preventing Bsph resistance.

Bacillus sphaericus (B.spi) strain 2362 has been recognized as a promising mosquito larvicide, and various preparations of this strain have been tested and used in mosquito control programs worldwide. This control agent has advantages of high efficacy, specificity, persistence, and environmental safety. However, resistance in Culex pipiens complex mosquitoes to Bsph has occurred in both laboratory and field populations, necessitating development of resistance management strategies. Studies were initiated aiming at reversing previously established Bsph resistance in a laboratory colony of Culex quinque fasciatus Say by selections with Bti alone, Bti and Bsph in rotation, or mixture. Partial restoration of susceptibility to Bsph was achieved by selection of resistant colony for 10 generations with Bti alone at LC80). After this colony was switched back to Bsph selection for 20 generations, resistance to Bsph partially increased to a stable level. Selections of Basph-resistant colonies with Bti and Bsph in rotation or mixture resulted in steady decline of resistance over 30 generations, with rapid decline in resistance noted in the initial 10-15 generations. It is interesting to note that selections with Bti and Bsph in rotation increased susceptibility to Bti in Bsph-resistant colony. It is promising that selection with Bti alone, Bsph and Bti in rotation, or mixture have a potential for developing practical strategies to overcome acquired resistance to Bsph in Cx. quinquefasciatus populations.

The primary mosquito species associated with underground stormwater systems in the United States are the Culex pipiens complex species. This group represents important vectors of West Nile virus (WNV) throughout regions of the continental U.S. In this study, we designed a mathematical model and compared it with surveillance data for the Cx. pipiens complex collected in Beaufort County, South Carolina. Based on the best fit of the model to the data, we estimated parameters associated with the effectiveness of public health insecticide (adulticide) treatments (primarily pyrethrin products) as well as the birth, maturation, and death rates of immature and adult Cx. pipiens complex mosquitoes. We used these estimates for modeling the spread of WNV to obtain more reliable disease outbreak predictions and performed numerical simulations to test various mosquito abatement strategies. We demonstrated that insecticide treatments produced significant reductions in the Cx. pipiens complex populations. However, abatement efforts were effective for approximately one day and the vector mosquitoes rebounded until the next treatment. These results suggest that frequent insecticide applications are necessary to control these mosquitoes. We derived the basic reproductive number (ℜ0) to predict the conditions under which disease outbreaks are likely to occur and to evaluate mosquito abatement strategies. We concluded that enhancing the mosquito death rate results in lower values of ℜ0, and if ℜ0

International audience; In Culex pipiens, overproduction of nonspecific esterases is a common mechanism of resistance to organophosphate insecticides 1,2. The esterases are attributed to closely linked loci named A and B according to substrate preference 3-6, and overproduction of all esterases B is due to gene amplification 7,8. Distribution of electrophoretically distinct variants of overproduced esterases A and B is geographically restricted, with the exception of esterases A2 and B2, always found together throughout at least three continents (Fig. 1). To determine whether this situation is due to migration or to a high mutation rate, esterase B structural genes and their flanking regions were compared by sequence and/or restriction fragment length polymorphism analysis. Whereas structural genes were similar, flanking regions of electrophoretically dissimilar esterases B varied considerably. In contrast, flanking sequences of esterases B2 from different geographical locations (Africa, Asia, North America) were identical. These results suggest that amplified esterase B2 genes originated from an initial event that has subsequently spread organophosphate insecticide resistance by migration.