Modeling Dynamics of Culex pipiens Complex Populations and Assessing Abatement Strategies for West Nile Virus

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<1, then an epidemic will not occur. Our modeling results provide insights about control strategies of the vector populations and, consequently, a potential decrease in the risk of a WNV outbreak.     

Susceptibility of Anopheles messeae Fall. and Culex pipiens pipiens L. Larvae to entomopathogenic Fungi Metarhizium

The mortality rate of Anopheles messeae Fll. and Culex pipiens pipiens L. mosquito larvae infected with entopathogenic fungi Metarhizium brunneum and M. robertsii has been studied in laboratory conditions. It was shown that C. pipiens larvae are more susceptible to a water suspension of fungal conidia treatment while A. messeae larvae are more susceptible to treatment with dry conodia. The mortality of mosquito larvae infected with the most virulent strain and dose of 2 × 10⁶ conidia per cm² was 87.5–92.5%. Prospects for the use of fungi in the biocontrol of bloodsucking mosquitoes are discussed.     

Mosquitocidal and repellent activities of essential oils against Culex pipiens L.

Plants are a prospective source of novel natural insect repellents and botanical insecticides. This study was conducted to investigate the chemical composition of the essential oils of three plants growing in Saudi Arabia, namely Ducrosia anethifolia, Achillea fragrantissima, and Teucrium polium; and to evaluate their potential mosquitocidal and repellent activities against adult female Culex pipiens L. The main components of the three oils were found to be decanal (28.9%) and chrysanthenyl acetate (10.04%), (D. anethifolia); sabinyl acetate (35.79) and artemesia ketone (18.28%) (A. fragrantissima); α‐cadinol (49.53%) and δ‐cadinene (10.23%) (T. polium). The oil of A. fragrantissima was the most toxic (LC₅₀ = 0.11 μL/L air) followed by D. anethifolia and T. polium with LC₅₀ values of 5.22 and 25.98 μL/L air, respectively. T. polium oil was the most repellent (292 min at 2 μL/cm²), followed by D. anethifolia and A. fragrantissima. The results indicate that the essential oils have a potential fumigant insecticidal and repellent activities for mosquito control.     

Esterases in the mosquito Culex pipiens pipiens L.: Formal genetics and polymorphism of adult esterases

The genetics of two esterase loci active in autogenous adults of the mosquito Culex pipiens pipiens L. has been studied by means of starch gel electrophoresis. Three alleles at the Est-1 locus and eight at the Est-2 locus are described. Both loci have a null allele. Active alleles are codominant and there is no hybrid enzyme in heterozygotes. The Est-1 locus codes esterases preferentially hydrolyzing -naphthylacetate and the Est-2 locus esterases preferentially hydrolyzing -naphthylacetate. Strains homozygous for both loci were selected. Linkage studies of the two loci have shown that they are not sex linked but are linked to each other, the crossover frequency being 8.6%. The polymorphism of two laboratory and two natural populations is described for both loci. Phenotypic distributions are in good agreement with Hardy-Weinberg expectations.This work was conducted at the Université des Sciences et Techniques du Languedoc (Laboratoire de Génétique Expérimentale des Populations), Montpellier, France, in partial fulfillment of the requirements for the degree of Docteur de spécialité.     

Multiple incompatibilities within populations of Culex pipiens L. in southern France

Strains of Culex pipiens derived from natural populations collected in southern France were crossed to determine their ability to give fertile offspring. Uni- and bi-directional incompatibilities occurred between these strains and each of them had its own crossing properties. Compatibility or incompatibility of a cross seemed to be related to the geographic distance separating the parental colonies, but not to their ecological origin (hypogeous or epigeous). Our results showed evidence for the variation in time of crossing properties of a strain.     

Vector competence of northern and southern European Culex pipiens pipiens mosquitoes for West Nile virus across a gradient of temperatures

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.     

Die entwicklung im normalen ei von Culex pipiens L. (Diptera)

Ohne Zusammenfassung     

Inherited preferential segregation in translocation heterozygotes of the mosquito,Culex pipiens L.

Summary The present paper deals with crossing experiments on translocation heterozygotes in the mosquitoCulex pipiens L. It is shown that the ratio of euploid and aneuploid gametes is determined by two allelomorphs of one single inheritable factor. These experiments agree with our hypothesis that the ratio of segregation types in a translocation heterozygous organism (alternate and adjacent) is determined by a series of multiple alleles of a single mendelian factor.The investigations were done in the Department of Biology (21) of the Johannes Gutenberg-University in Mainz.     

Vector Competence of American Mosquitoes for Three Strains of Zika Virus

In 2015, Zika virus (ZIKV; Flaviviridae; Flavivirus) emerged in the Americas, causing millions of infections in dozens of countries. The rapid spread of the virus and the association with disease outcomes such as Guillain-Barré syndrome and microcephaly make understanding transmission dynamics essential. Currently, there are no reports of vector competence (VC) of American mosquitoes for ZIKV isolates from the Americas. Further, it is not clear whether ZIKV strains from other genetic lineages can be transmitted by American Aedes aegypti populations, and whether the scope of the current epidemic is in part facilitated by viral factors such as enhanced replicative fitness or increased vector competence. Therefore, we characterized replication of three ZIKV strains, one from each of the three phylogenetic clades in several cell lines and assessed their abilities to be transmitted by Ae. aegypti mosquitoes. Additionally, laboratory colonies of different Culex spp. were infected with an American outbreak strain of ZIKV to assess VC. Replication rates were variable and depended on virus strain, cell line and MOI. African strains used in this study outcompeted the American strain in vitro in both mammalian and mosquito cell culture. West and East African strains of ZIKV tested here were more efficiently transmitted by Ae. aegypti from Mexico than was the currently circulating American strain of the Asian lineage. Long-established laboratory colonies of Culex mosquitoes were not efficient ZIKV vectors. These data demonstrate the capacity for additional ZIKV strains to infect and replicate in American Aedes mosquitoes and suggest that neither enhanced virus replicative fitness nor virus adaptation to local vector mosquitoes seems likely to explain the extent and intensity of ZIKV transmission in the Americas.     

Screening and evaluation of different algal extracts and prospects for controlling the disease vector mosquito Culex pipiens L.

Continual application of synthetic insecticides in controlling mosquito larvae has resulted in several problems as build-up of mosquito resistance beside to negative impacts on human health and environment. Discovering new and affordable bio-insecticidal agents with high efficiency, cost effective and target specific become a crucial need. The current study assessed the larvicidal activity of eight methanolic algal extracts belong to three different algal divisions against the 3^rd larval instar of Culex pipiens L. (Diptera: Culicidae). Comparative studies showed that four species of red and green algal extracts exhibited good larvicidal activity. Galaxaura elongata and Jania rubens (Rhodophyta), Codium tomentosum and Ulva intestinales (Chlorophyta) showed higher larvicidal potencies than Padina boryana, Dictyota dichotoma, and Sargassum dentifolium (Phaeophyta) and Gelidium latifolium (Rhodophyta). The maximum level of toxicity was achieved by exposure to G. elongata extract with LC₅₀ (31.13 ppm), followed by C. tomentosum (69.85 ppm) then J. rubens (84.82 ppm) and U. intestinalis (97.54 ppm), while the lowest toxicity exhibited by G. latifolium (297.38 ppm) at 72 h post- treatment. The application of LC₅₀ values of G. elongate, J. rubens, C. tomentosum, and U. intestinalis extracts affected the activities of antioxidant enzymes viz. superoxide dismutase, catalase and glutathione peroxidase as oxidative stress markers. An increase of antioxidant enzymes activities was recorded. Therefore, a significant elimination of free radicals, causing toxic effects. Overall, this study casts light on the insecticidal activity of some algal extracts, suggesting the possibility of application of these bio- agents as novel and cost- effective larvicides.     

Detection of Japanese Encephalitis Virus Genotype V in Culex orientalis and Culex pipiens (Diptera: Culicidae) in Korea

Japanese encephalitis virus (JEV) causes significant viral encephalitis and is distributed throughout the Asian countries. The virus is known to be transmitted by Culex tritaeniorhynchus, which mainly breeds in rice paddies in Korea. In this study, we investigated the presence of other mosquito species that can transmit JEV as a second or regional vector. We selected five cities where patients have experienced JE in the last 5 years as mosquito-collecting locations and subdivided them into four collection sites according to the mosquito habitats (cowshed, downtown area, forest, and swamp). Mosquitoes were caught using the BG-Sentinel trap, CDC black-light trap, Fay-Prince trap, and Gravid trap. A total of 993 pools from 22,774 mosquitoes were prepared according to their species, collection date, and site. We performed a SYBR Green 1-based real-time RT-PCR assay to detect JEV from the mosquito pools. A total of six JEV-positive pools were detected from Culex orientalis and Culex pipiens caught in the Gangwon-do and Gyeonngi-do provinces. All the detected JEVs were revealed as genotype V by phylogenetic analysis of the envelope gene. Our findings confirm that a new genotype of JEV was introduced in Korea and suggest that two mosquito species may play a role in JEV transmission.     

Viability of Culex pipiens pipiens eggs affected by nutrition and aposymbiosis

Raisins were a better source of carbohydrate than sucrose for reproduction by autogenous Culex pipiens. A blood meal increased the number of eggs per raft from 49 autogenously to 114. Eggs of aposymbiotic females produced autogenously did not hatch, but 34% of the eggs were viable if the mosquitoes fed on chickens. With repeated blood meals the number of eggs per raft and the rate of embryonation and hatching declined in each successive gonotrophic cycle. In about $\text{1}\text{4}$ of the unhatched eggs of normal females there were no fully developed embryos, while many more of the unhatched eggs of aposymbiotic females contained no evidence of embryonic development. After the fifth blood meal, neither normal nor aposymbiotic insects oviposited. The ovaries of the nulliparous females contained approximately 10% of the potential number of mature terminal oocytes. Proximally in the ovarioles there were dilatations and coiled tracheoles indicating egg resorption. There were fewer parous follicles in aposymbiotic than in normal females. Larval rearing water, i.e., infusion in which larvae had been reared, was more attractive than fresh infusion for oviposition by normal, autogenous mosquitoes. The degree of embryonation of the eggs was lower and the hatching success rate was poorer in fresh infusion than in larval rearing water.