Form Molestus Research Articles

Studies On the Origin of Culex pipiens pipiens Form Molestus in New York City

Culex pipiens pipiens is comprised of two forms: Cx. pipiens pipiens form pipiens and Culex pipiens pipiens form molestus. One population of Cx. p. pipiens form molestus in the United States, located in the 91st Street sewer of New York City (NYC), has been relatively well-characterized. The objective of this review is to summarize the results of multiple independent studies on Cx. p. pipiens form molestus in NYC and present the current understanding of the origin of this population. While solid evidence exists supporting the genetic differentiation and population structuring between Cx. p. pipiens form pipiens and form molestus in NYC, the possibility that the 91st St. sewer population of form molestus was founded by local aboveground Cx. p. pipiens form pipiens cannot be ruled out based on available data to date. Future studies in the US should include sympatric populations of both forms of Cx. p. pipiens from around the world in order to provide the necessary context to resolve these phylogenetic relationships.

The Culex pipiens Complex in Continental Portugal: Distribution and Genetic Structure

Portugal is a southern European country that displays favorable ecological conditions for the establishment of West Nile virus (WNV) transmission cycles. Competent mosquito vector species are present throughout the country. Among the species with reported cases of WNV isolation in Portugal, Culex pipiens is the most ubiquitous and abundant mosquito. This species exhibits two biological forms with differences in host preferences. The molestus form has a greater tendency to feed upon humans and other mammals whereas the pipiens form prefers avian hosts. In northern latitudes, both forms are physically separated, with molestus occupying underground habitats and pipiens being found aboveground. However, the warmer climatic conditions of southern regions such as Portugal may favor the sympatric occurrence of both forms hence promoting interform hybridization. Genetic introgression between molestus and pipiens forms may result in a higher propensity for admixed populations to serve as bridge-vectors of WNV between humans and birds. Here we revise our present knowledge on the distribution, role in WNV transmission and genetic structure of the Cx. pipiens complex in continental Portugal. We focus on recent findings of sympatric molestus and pipiens populations that display considerable levels of hybridization and discuss the epidemiological repercussions of this occurrence.

The Forms of the Culex pipiens Complex in East Asia, with Ecological Thoughts on Their Origin and Interrelation

In East Asia, 4 forms of the Culex pipiens complex have been confirmed. A form pipiens s. s. (anautogeous pipiens) has been confirmed only in westernmost China. A temperate form pallens and a subtropical and tropical form quinquefasciatus are connected with intermediates in morphology and many aspects of ecology, but their difference is rather clear in climatic adaptation traits. The distribution of a form molestus overlaps with pallens and, in Taiwan, quinquefasciatus, and, in East Asia, this form requires artificial underground habitats for its persistence. The origin and interrelation of 3 forms other than pipiens s. s. are considered from ecological aspects, especially climatic adaptation. A hypothesis is presented that molestus was originally a form having adapted to the Mediterranean climate in the western Palaearctic, secondarily colonized artificial underground habitats, and reached East Asia in the early 20th century by ships from North America. At present, it is difficult to assign pallens with certainty to either the old or new groups of the Manchurian mosquito fauna. Three hypotheses about the interrelation between pallens and quinquefasciatus are compared, and the strengths and problems of each hypothesis are indicated. Finally, a map to show the distribution of the forms of the Culex pipiens complex before it was extensively changed by humans is presented as an initial trial. The Culex pipiens problems now troubling humans are largely human-made problems.

Diversity of Wolbachia pipientis strain wPip in a genetically admixtured, above-ground Culex pipiens (Diptera: Culicidae) population: association with form molestus ancestry and host selection patterns.

Analysis of molecular genetic diversity in nine marker regions of five genes within the bacteriophage WO genomic region revealed high diversity of the Wolbachia pipentis strain wPip in a population of Culex pipiens L. sampled in metropolitan Chicago, IL. From 166 blood fed females, 50 distinct genetic profiles of wPip were identified. Rarefaction analysis suggested a maximum of 110 profiles out of a possible 512 predicted by combinations of the nine markers. A rank-abundance curve showed that few strains were common and most were rare. Multiple regression showed that markers associated with gene Gp2d, encoding a partial putative capsid protein, were significantly associated with ancestry of individuals either to form molestus or form pipiens, as determined by prior microsatellite allele frequency analysis. None of the other eight markers was associated with ancestry to either form, nor to ancestry to Cx. quinquefasciatus Say. Logistic regression of host choice (mammal vs. avian) as determined by bloodmeal analysis revealed that significantly fewer individuals that had fed on mammals had the Gp9a genetic marker (58.5%) compared with avian-fed individuals (88.1%). These data suggest that certain wPip molecular genetic types are associated with genetic admixturing in the Cx. pipiens complex of metropolitan Chicago, IL, and that the association extends to phenotypic variation related to host preference.

Molecular evidence of Culex pipiens form molestus and hybrids pipiens/molestus in Morocco, North Africa.

BackgroundCulex pipiens L. is the most widespread mosquito vector in temperate regions including North Africa. Cx. pipiens has two recognized forms or biotypes; pipiens and molestus are morphologically indistinguishable with distinct behavior and physiology that may influence their vectorial status. In our study, we prospected for the different forms of Cx. pipiens in Morocco.MethodsCx. pipiens larvae were collected in 9 sites throughout Morocco during summer 2010 and reared until imago stage. Cx. pipiens was identified using diagnostic primers designed for the flanking region of microsatellite CQ11.ResultsWe established the presence of both forms of Cx. pipiens and their hybrids in Morocco.ConclusionsMolecular identification provides the first evidence of the presence of Cx. pipiens form molestus in Morocco and hybrids between pipiens and molestus forms in North Africa. The epidemiological implications of our findings are discussed.

Host-Feeding Habits of <I>Culex pipiens</I> and <I>Aedes albopictus</I> (Diptera: Culicidae) Collected at the Urban and Suburban Residential Areas of Japan

To evaluate the vectorial capacity of mosquitoes for viruses in Japan, the host-feeding habits of the mosquitoes were analyzed by sequencing polymerase chain reaction-amplified fragments of the cytochrome b and 16S ribosomal RNA regions of the mitochondrial DNA of 516 mosquitoes of 15 species from seven genera that were collected from residential areas during 2003-2006. Culex pipiens L. and Aedes albopictus Skuse were the most commonly collected species in urban and suburban residential areas. Anautogenous Culex pipiens pallens Coquillett was distinguished from the autogenous Cx. pipiens form molestus Forskal using a polymerase chain reaction-based identification method. Both Cx. p. pallens and Cx. p. form molestus exhibited similar host-feeding habits, broadly preferring avian (50.0 and 42.5% of avian, respectively) and mammalian (38.6 and 45.0% of avian, respectively) hosts, such as tree sparrows, ducks, and humans. Conversely, Ae. albopictus exhibited a highly mammalophilic and anthropophilic feeding pattern, with 84.2% feeding on mammalian hosts and 68.5% of these on humans. We concluded that in Japan, Cx. pipiens might play a significant role in the avian-to-mammal transmission of viruses, such as West Nile virus, whereas Ae. albopictus might play a role in the human-human transmission of dengue and Chikungunya viruses.

Effect of light and temperature on the daily rhythm of adult eclosion in the blood-sucking mosquitoes Aedes communis De Geer and Culex pipiens L. (Diptera, Culicidae)

A comparative study on the effect of light and temperature on the daily rhythm of adult eclosion was carried out on the blood-sucking mosquitoes Aedes (Ochlerotatus) communis De Geer and Culex pipiens pipiens L. Two forms of C. p. pipiens were investigated: the autogenous form molestus occurring in the underground habitats (the urban mosquito), and the anautogenous form pipiens inhabiting mostly the above-ground biotopes. The study included both field observations and laboratory experiments. Under natural conditions (southern Karelia, 62°N) at optimal temperatures A. communis and C. p. p. f. pipiens demonstrated a bimodal eclosion rhythm with morning and evening peaks, whereas in C. p. p. f. molestus only an evening maximum was observed. The fraction of adults eclosing in the middle of the day increased at lower temperatures. In all the mosquitoes studied, the daily eclosion dynamics in the nature did not differ significantly between the variants with different levels of illumination, suggesting that temperature was the main factor regulating the eclosion rhythm. However, experiments with constant temperature showed that light also could influence the timing of eclosion. The responsiveness to light was different in two studied forms of C. p. pipiens. Under a constant temperature and light-dark cycles the rhythm became weak or disappeared completely in the mosquitoes from above-ground biotopes (A. communis and C. p. p. f. pipiens) but persisted in the urban mosquito. The effect of gradual twilight transitions was more prominent than that of switching the light on or off abruptly. The observed differences in the light and temperature dependence of the eclosion rhythm are discussed in relation to the ecological conditions in different habitats.

The characteristics of the most troublesome mosquito species (Diptera: Culicidae) in Poland

Twelve of the 47 Polish mosquito species can pose serious health problems to man or at least heavy nuisance. They fly from breeding sites (where huge numbers can be produced) into houses and/or farm buildings transmitting severe human and animal diseases. Problematic ones are: Anopheles messae and An. atroparvus, Ochlerotatus communis, Oc. cataphylla, Oc. punctor, Oc. cantans, Oc. sticticus, Aedes cinereus, Ae. vexans, Coquillettidia richiardii, Culex pipiens and Culiseta annulata. The problems of distribution, phenology under different climatic conditions, habitat requirements and preferences both of larvae and adults, behaviour, fertility and vector competence of all these species are analyzed. Most of the species in the Temperate Zone produce more than one generation during the growing season or at least have several emergences. Only Oc. communis and Oc. cataphylla are early spring univoltine species, although they can breed twice or more during the growing season when there are favourable conditions. Univoltine Oc. cantans, which can develop several times during a season, occurring in the breeding sites often together with multivoltine Oc. punctor. The period of their occurrence is usually much longer than that of Oc. communis and Oc. cataphylla. Flood-water mosquitoes - Oc. sticticus and both Aedes species occur along river valleys and their larvae can breed in different pools situated in a variety of environments. Culex pipiens, especially its form molestus and Culiseta annulata can breed in natural and artificial ponds, even in heavily polluted water. Although mosquitoes are known to be competent vectors of serious human and animal diseases, in Poland they are considered to cause nuisance only. Despite the fact that malaria was eradicated in Poland in 1960-s, at least two Polish anopheline species can still transmit the human malarial parasite very effectively. The remaining species (except for only one) described in the paper can transmit several arboviruses, while several species are vectors of filariosis (Dirofilaria sp.).

PCR-Based Identification of <i>Culex pipiens</i> Complex Collected in Japan

The Culex pipiens complex consists of vector mosquitoes that transmit important human pathogens. In this study we established a simplified method to distinguish three members of the Cx. pipiens complex, Cx. p. pallens Coquillet, Cx. p. form molestus Forskal, and Cx. quinquefasciatus Say, collected in Japan. Sequence analysis of the Drosophila Ace-orthologous acetylcholinesterase (Ace) gene (668 to 680 bp) revealed that a single polymorphic region characterizes each species. Based on this region, specific primers that distinguish Cx. p. form molestus (ACEpip2) and Cx. p. pallens (ACEpall2) were newly designed. Polymerase chain reactions were performed with the genomic DNA of Culex mosquitoes as the template, and these primers clearly distinguished two Culex spp. The accuracy of the designed primers was evaluated with 38 colonies of mosquito samples collected from 9 prefectures of Japan. The testing revealed that the distribution of anautogenous Cx. p. pipiens has not been confirmed in Japan. It also revealed that the male of Cx. p. pallens possesses an Ace gene haplotype that is highly similar to the sequence of Cx. quinquefasciatus. This improved method allows the evaluation of vector competence of Cx. p. form molestus, which is the suspected vector of West Nile virus.

Genetic Influences on Mosquito Feeding Behavior and the Emergence of Zoonotic Pathogens

The feeding behavior of vectors influences the likelihood of pathogen invasion and the exposure of humans to vector-borne zoonotic pathogens. We used multilocus microsatellite genetic typing of an introduced mosquito vector and DNA sequencing of mosquito blood meals to determine the impact of hybrid ancestry on feeding behavior and the emergence of West Nile virus (WNV). The probability of ancestry of Culex pipiens mosquitoes from two bionomically divergent forms, form molestus and form pipiens, influenced the probability that they fed on humans but did not explain a late summer feeding shift from birds to humans. We used a simple model to show that the occurrence of pure form molestus mosquitoes would have decreased the likelihood of WNV invasion (R(0) in bird populations) 3- to 8-fold, whereas the occurrence of pure forms pipiens mosquitoes would have halved human exposure compared with the hybrids that are present. Data and modeling suggest that feeding preferences may be influenced by genetic ancestry and contribute to the emergence of vector-borne pathogens transmitted by introduced species, including malaria, and dengue, Chikungunya, yellow fever, and West Nile viruses.

Insecticide Resistance in Potential Vector Mosquitoes for West Nile Virus in Japan

Culex pipiens complex is the significant vector mosquito of West Nile virus. To take stock of the current situation of insecticide susceptibilities and design an ideal mosquito control strategy, we collected Culex pipiens pallens Coquillet, Culex pipiens form molestus Forskal, and Culex quinquefasciatus Say from fields in Japan and conducted bioassays for five larvicides (fenitrothion, temephos, etofenprox, diflubenzuron, and pyriproxyfen) by using a larval dipping method. Among five insecticides tested, obvious reduced susceptibilities were observed for etofenprox, which is the only pyrethroid compound registered as a larvicide in Japan. Twenty-two of 56 colonies exhibited a >10% survival rate at the etofenprox concentration of 5.7 microg/ml, which is a 10 times higher concentration of the working solution. The LC50 of a colony collected from Fukuoka prefecture for etofenprox exceeded 60 microg/ml (resistance ratio >2,307), and this colony also exhibited cross-resistance to other pyrethroids, permethrin (299-fold) and phenothrin (1,200-fold). The insect growth regulators diflubenzuron and pyriproxyfen were found to be sufficiently effective enough to control Culex larvae present, but decreased sensitivities to these insecticides were slightly detected in some colonies of Cx. p. form molestus collected from urban areas. Several etofenprox-resistant colonies of Cx. p. form molestus exhibited simultaneously decreased susceptibilities to other insecticides, including temephos, diflubenzuron, and pyriproxyfen.

Genetic Differences Between <I>Culex pipiens</I> f. molestus and <I>Culex pipiens pipiens</I> (Diptera: Culicidae) in New York

The definition and phylogenetic placement of the autogenous molestus form of Culex pipiens has puzzled entomologists for decades. We identified genetic differences between Cx. p. pipiens (L.) and Cx. pipiens f. molestus Forskål in the SH60 fragment described previously. Single-strand conformation polymorphism analysis, cloning, and sequencing of this fragment demonstrated high polymorphism within and among individual Cx. p. pipiens, with common SH60 variants shared among individuals from distant locations. In contrast, Cx. pipiens f. molestus from New York City each contained a single SH60 variant, which was not identified in any other Cx. p. pipiens specimens analyzed. Supporting microsatellite analysis demonstrated significant but reduced gene flow between Cx. p. pipiens and Cx. pipiens f. molestus in New York relative to Cx. p. pipiens populations in New York and California. Results are discussed in the context of two contrasting hypotheses regarding the origin of Cx. pipiens f. molestus populations.

Laboratory Transmission of Japanese Encephalitis and West Nile Viruses by Molestus Form of Culex pipiens (Diptera: Culicidae) Collected in Uzbekistan in 2004

Abstract We evaluated the molestus form of Culex pipiens pipiens (L.) (hereafter referred to as "molestus") captured near Tashkent, Uzbekistan, for their ability to transmit Japanese encephalitis (family Flaviviridae, genus Flavivirus, JEV) and West Nile (family Flaviviridae, genus Flavivirus, WNV) viruses under laboratory conditions. These molestus were highly competent laboratory vectors of WNV, with infection and dissemination rates of 96 and 81%, respectively. Approximately 75% of female molestus that fed after development of a disseminated infection transmitted virus by bite. Therefore, ≈60% of those molestus taking a second bloodmeal between 16 and 25 d after an infectious bloodmeal would be expected to transmit WNV by bite. In contrast, these molestus were less efficient vectors of JEV, with infection and dissemination rates of 51 and 25%, respectively. In addition, only 33% of individuals with a disseminated infection transmitted JEV by bite, indicating a significant salivary gland barrier. Therefore, only ≈8% of orally exposed individuals would be expected to transmit JEV by bite if they took a second bloodmeal 16–25 d later. These data indicate that the molestus form of Cx. p. pipiens should be considered a potentially important vector of WNV in Uzbekistan and may become involved in the transmission of JEV, should this virus be introduced into Uzbekistan.

Laboratory Transmission of Japanese Encephalitis and West Nile Viruses by Molestus Form of <I>Culex pipiens</I> (Diptera: Culicidae) Collected in Uzbekistan in 2004

We evaluated the molestus form of Culex pipiens pipiens (L.) (hereafter referred to as "molestus") captured near Tashkent, Uzbekistan, for their ability to transmit Japanese encephalitis (family Flaviviridae, genus Flavivirus, JEV) and West Nile (family Flaviviridae, genus Flavivirus, WNV) viruses under laboratory conditions. These molestus were highly competent laboratory vectors of WNV, with infection and dissemination rates of 96 and 81%, respectively. Approximately 75% of female molestus that fed after development of a disseminated infection transmitted virus by bite. Therefore, approximately 60% of those molestus taking a second bloodmeal between 16 and 25 d after an infectious bloodmeal would be expected to transmit WNV by bite. In contrast, these molestus were less efficient vectors of JEV, with infection and dissemination rates of 51 and 25%, respectively. In addition, only 33% of individuals with a disseminated infection transmitted JEV by bite, indicating a significant salivary gland barrier. Therefore, only approximately 8% of orally exposed individuals would be expected to transmit JEV by bite if they took a second bloodmeal 16-25 d later. These data indicate that the molestus form of Cx. p. pipiens should be considered a potentially important vector of WNV in Uzbekistan and may become involved in the transmission of JEV, should this virus be introduced into Uzbekistan.

Polymorphism of mitochondrial DNA and infection with symbiotic cytoplasmic bacterium Wolbachia pipientis in mosquitoes of the Culex pipiens (Diptera, Culicidae) complex from Russia

A total of 208 mosquitoes of the Culex pipiens complex from 15 basement and terrestrial populations collected in different regions of the European part of Russia and Siberia were examined by genetic methods. Among these, two major mitotypes, M and P, were identified. These mitotypes differed by six substitutions in the 246-bp mitochondrial DNA cytochrome oxidase I gene fragment examined. Urban basement mosquitoes C. pipiens (form molestus) were characterized by the presence of mitotype M and infection with the endosymbiotic bacteria of the genus Wolbachia. Mosquitoes of the C. pipiens complex inhabiting opened biotopes harbored mitotype P, or its variety, mitotype P1, and were not infected with Wolbachia. Thus, in natural conditions marked linkage disequilibrium between cytoplasmic elements, mitochondrial DNA and Wolbachia, can be observed. Similarity of mitotypes in form molestus mosquito from different geographical localities favors the hypothesis on the common ancestry of urban mosquitoes.

Surface films as mosquito larvicides: partitioning the mode of action

AbstractOils and other surface films used against mosquito larvae may act by flooding the tracheal system with oil, by disrupting the surface forces that allow larvae to rest at the surface, by toxicity, or by eliciting chemosensory responses. In an attempt to identify diagnostic symptoms of these modes of action we treated fourth‐stage larvae of Culex pipiens L. form molestus Forskål (Diptera: Culicidae: Culicinae) with agents operating in a single mode (Ondina oil for flooding with oil, nicotine for toxicity, and the detergent Triton X‐100 for disruption of surface forces), in two modes (silicone oil) or in three (eucalyptus oil, citronellal, or caproic acid ethyl ester). We monitored the time course of flooding and immobilisation, used experiments to separate volatile toxicity from toxicity of the aqueous solution, and used video and The Observer software to analyse larval behaviour.Larvae that experienced tracheal flooding applied their mouthparts to the siphon (tail nibbling), often losing contact with the surface while doing so and falling to the bottom. Nicotine immobilised larvae without interfering with surface forces, and the larvae remained immobile hanging from the air‐water interface for long periods. In detergent, larvae made repeated unsuccessful attempts to thrust the siphon through the surface. The behaviour‐modifying chemicals caproic acid ethyl ester, eucalyptus oil and citronellal all operated in more than one mode. They all decreased the proportion of time larvae spent at the surface, whereas Ondina oil and silicone fluid increased it.Using this approach it should be possible to identify the modes of action of novel larvicidal agents. This could form a basis for rational design of larvicides giving an optimal compromise between efficacy against mosquito larvae and minimal damage to non‐target organisms.

Culex pipiens in London Underground tunnels: differentiation between surface and subterranean populations.

Genetic variation was quantified between surface-dwelling populations of Culex pipiens and the so-called molestus form found in the London Underground (the Underground) railway system. The molestus form is a commercially important biting nuisance and in the southern part of its range is also a disease vector. The surface and subterranean populations were genetically distinct, with no evidence of gene flow between closely adjacent populations of the different forms, whereas there was little differentiation between the different populations of each form. The substantially reduced heterozygosity in the Underground populations and the allelic composition suggest that colonization of the Underground has occurred once or very few times. Breeding experiments show compatibility between the Underground populations but not with those breeding above ground. There is evidence of greater gene flow and a mixing of molestus and pipiens traits in the south of the species range. This paper considers the processes that may allow establishment of reproductive isolation in the north of the species range but not in the south.

Ecological and geographical variations in the siphonal index of Culex pipiens larvae (Diptera: Culicidae)

AbstractCulex pipiens Linnaeus is represented by two forms: the form molestus which is autogenous, stenagamous and has no reproductive diapause, and the form pipiens which is anautogenous, eurygamous and diapauses. The ecological, physiological and geographical variations in the larval siphonal index of C. pipiens (the ratio of the length of the siphon to its width at the base) was investigated using both original measurements and previously published data. In all, data were used from 259 collections from open water bodies (marshes, ditches, holes, barrels, etc.) and underground waters (house basements) in areas of Europe, Asia and part of Africa. Autogeny was studied in some cases by dissection of females. In C. pipiens the mean siphonal index was strongly correlated with ecology (water body type) and adult physiology (autogeny). In spite of high geographical and individual variation, which makes the identification of individual larvae difficult, the mean siphonal index can be used with certainty for the differentiation of populations of the two forms of C. pipiens.

Spacing behaviour in resting Culex pipiens (Diptera, Culicidae): a computer modelling approach

Abstract. We compared two models based on Monte Carlo simulations with the spacing patterns of resting adults of the mosquito Cx pipiens L. (form molestus) (Diptera, Culicidae). The comparison with the first model which assumed a distribution of complete spatial randomness showed that there was a tendency for mosquitoes to repel other mosquitoes which were too close, resulting in high local regularity. The second model took this repulsion into account. A final test of global patchiness using Model 2 indicated that the spacing behaviour of Cx pipiens was not sufficiently described by local regularity only, but also required a gregarious element. This supports the hypothesis that the molestus form of Cx pipiens shows spaced‐out gregariousness in the sense of Kennedy & Crawley (1967).

Integration of radiation with cytoplasmic incompatibility for genetic control in the Culex pipiens complex (Diptera: Culicidae).

Crosses between Culex pipiens form molestus and Cx. quinquefasciatus confirmed bidirectional incompatibility between them. In a genetic control operation the risks of release of fertile females could be avoided by irradiation, but complete sterilization of Cx. p. form molestus females required a higher dose (7 kR) than did Cx. quinquefasciatus females (6 kR). The unirradiated molestus males competed equally with unirradiated quinquefasciatus males, but the irradiated molestus males showed significantly reduced competitiveness.