Comparison of different trapping methods for surveillance of mosquito vectors of West Nile virus in Rhône Delta,France

Five trapping methods were compared for monitoring potential vectors of the West Nile virus in four areas in the Camargue Plain of France: carbon dioxide traps, bird‐baited traps, gravid traps, resting boxes, and human landing catches. A total of 73,721 specimens, representing 14 species, was trapped in 2006. Results showed significant differences in species and abundance between the type of traps. Many more specimens were collected using CO₂ traps than any other method, with an average of 212 specimens per night per trap (p<0.05). Culex pipiens was the most abundant species collected (36.8% of total with CO₂ traps), followed by Aedes caspius (22.7%), Anopheles hyrcanus (18.3%), Culex modestus (18.3%), and Aedes detritus (3.2%). Bird‐baited traps captured only eight specimens per night per trap on average, mainly Cx. pipiens (89.9%). The species collected and their abundance are influenced by the trap location, at ground or canopy level. Culex pipiens was twice as abundant in the canopy as on the ground, whereas it was the opposite for Ae. caspius, An. hyrcanus, and Ae. detritus. Culex modestus was equally abundant at both levels. Resting boxes and gravid traps were much less efficient, capturing around 0.3 specimens per night per trap. Results are discussed in relation to West Nile virus surveillance.     

The arbovirus vector Culex torrentium is more prevalent than Culex pipiens in northern and central Europe

Two species of arbovirus vector, Culex torrentium and Culex pipiens (Diptera: Culicidae), occur in several European countries, but difficulties in their accurate identification and discrimination have hampered both detailed and large‐scale distribution and abundance studies. Using a molecular identification method, we identified to species 2559 larvae of Cx. pipiens/torrentium collected from 138 sites in 13 European countries ranging from Scandinavia to the Mediterranean coast. In addition, samples of 1712 males of Cx. pipiens/torrentium collected at several sites in the Czech Republic were identified to species based on the morphology of their hypopygia. We found that the two species occur together in large areas of Europe, and that Cx. torrentium dominates in northern Europe and Cx. pipiens dominates south of the Alps. The transition in dominance occurs in central Europe, where both species are roughly equally common. There was a strong correlation between the length of the growing season at different sites and occurrences of the two species. As the growing season increases, the proportion and detection of Cx. torrentium decrease, whereas those of Cx. pipiens increase. The present findings have important consequences for the interpretation of the results of studies on major enzootic and link‐vectors of mosquito‐borne bird‐associated viruses (i.e. Sindbis, West Nile and Usutu viruses), especially in central Europe and Scandinavia.     

Wide recognition of Culex pipiens and lack of detection of Culex torrentium through biomolecular differentiation of mosquitoes in the Emilia‐Romagna region,Northern Italy

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.     

The relative attractiveness of carbon dioxide and octenol in CDC- and EVS-type light traps for sampling the mosquitoes Aedes aegypti (L.), Aedes polynesiensis Marks, and Culex quinquefasciatus say in Moorea, French Polynesia.

Two dominant day-biting pests and vector species on the island of Moorea in French Polynesia are Aedes (Stegomyia) aegypti (L.) and Aedes (Stegomyia) polynesiensis Marks, major vectors of dengue viruses and Wuchereria bancrofti, respectively. Their surveillance is hindered by a relative lack of attraction to light traps, necessitating the undesirable use of human bait collections with the inherent risks of pathogen transmission. The effectiveness of CDC- and EVS-type light traps baited with olfactory attractants was evaluated for these two Aedes species and the nocturnal Culex (Culex) quinquefasciatus Say in three sites in urban and semi-rural environments on Moorea in October/November 2003. Firstly, four CDC-type traps with light only, light with octenol, light with carbon dioxide (dry ice), and light with octenol plus carbon dioxide were operated continuously over four days with daily rotation to compensate for position effects. Secondly, two CDC- and two EVS-type traps with carbon dioxide or carbon dioxide plus octenol were operated continuously over four days with similar rotation. Variation was found in the numbers of the three species collected at the different sites, reflecting the relative availability of their preferred larval habitats. With the CDC traps in the first trial, the addition of octenol to the light did not significantly increase the collection of any species, the addition of carbon dioxide did significantly increase collection of all three species, while the addition of octenol to the light plus carbon dioxide did not significantly increase the collections further. In the second trial, there was no significant difference in the mean number of Ae. aegypti or Ae. polynesiensis collected in either EVS or CDC traps when baited with carbon dioxide or with octenol added. For Cx. quinquefasciatus, the supplementation with octenol made no significant difference with EVS traps but resulted in significantly reduced collections in CDC traps. Overall, neither trap, however baited, provided large samples when compared with landing/ biting collections at human bait. Only two other species were collected, Culex (Culex) roseni Belkin and Aedes (Aedimorphus) nocturnus (Theobald), the latter being a first record for the island of Moorea and for French Polynesia.     

Evaluation of various attributes of gravid female traps for collection of Culex in Florida.

Gravid female traps are used for surveillance of populations of Culex spp. and arboviruses such as West Nile virus. Field trials evaluating various attributes of gravid female traps for collection of gravid Culex were conducted in rural habitats in Alachua and Marion Counties, FL. Screened cage tests in the field were also used to compare trap models. Three trap models were evaluated: two based on the original Reiter design (Gravid CDC traps A and B) and one based on the revised Reiter design (gravid box trap). Trap model significantly affected collection of Culex quinquefasciatus and Culex nigripalpus; the greatest numbers were collected by the CDC gravid trap Aand CDC gravid trap B traps compared to the gravid box traps. There were no statistically significant differences between the collections with CDC gravid traps A and B. These patterns were similar at both sites and between early and late summer collections in Marion Co. In trials conducted in screened field cages with gravid Cx. quinquefasciatus, significantly more mosquitoes were collected in the CDC gravid trap A and B than in box gravid traps. Size of pan associated with the gravid traps was important and traps with larger pans collected more mosquitoes. Pan color was also important in efficacy of traps, and traps with darker pans (black, green) collected more mosquitoes than traps with lighter pans (tan, white). The percentages of gravid mosquitoes in trap collections of Culex females ranged from 54.0% to 89.6% with no clear differences between model of trap, size of pan, or pan color. Various attributes of gravid female traps impact the efficacy of the traps for Culex spp. and these should be considered in trapping programs.     

The response of Culex quinquefasciatus (Diptera: culicidae) to traps baited with carbon dioxide, 1-octen-3-ol, acetone, butyric acid and human foot odour in Tanzania

The responses of Culex quinquefasciatus Say to traps baited with carbon dioxide, 1-octen-3-ol, acetone, butyric acid and human foot odour were studied in the field in Muheza, north-east Tanzania using Counterflow Geometry (CFG) and Centers for Disease Control (CDC) traps. It was found that significantly more C. quinquefasciatus responded to foot odour collected on nylon stockings than to clean nylon stockings (P < 0.05). Significantly more mosquitoes were caught in a CFG trap baited with carbon dioxide than in traps with either human foot odour, acetone or butyric acid. It was also found that in an outdoor situation a carbon dioxide baited CDC unlit trap collected over 12 times more C. quinquefasciatus than an unbaited CDC unlit trap and nine times more mosquitoes than CDC traps baited with 1-octen-3-ol alone (P < 0.05). The number of mosquitoes caught in a CDC trap baited with 1-octen-3-ol did not differ significantly from that of the unbaited CDC trap (P > 0.05). These results indicate that the Afrotropical C. quinquefasciatus respond significantly better to traps baited with carbon dioxide than to either octenol, acetone or butyric acid, and that human foot odour contains stimuli to which C. quinquefasciatus is attracted under field conditions.     

A sensitive and reliable restriction enzyme assay to distinguish between the mosquitoes Culex torrentium and Culex pipiens

Culex pipiens pipiens Linnaeus and Culex torrentium Martini (Diptera: Culicidae) are closely related vector species that exist sympatrically in Europe. The two species are morphologically almost identical and can only be distinguished with certainty by characters of the male genitalia. Hence, correct species identification and conclusions on distribution and vector status are very difficult and often neglected. Therefore, we developed a reliable and simple mitochondrial cytochrome c oxidase subunit I (COI) gene restriction enzyme assay to discriminate between Cx. pipiens and Cx. torrentium, based on the analysis of morphologically identified male specimens. We sequenced approximately 830 bp in the 3′ region of the mitochondrial COI gene of 18 morphologically identified males of Cx. pipiens and Cx. torrentium. Two restriction enzymes (FspBI and SspI) that could distinguish between the two species according to species‐specific differences in these sequences were chosen. The restriction enzymes were tested on 227 samples from Sweden and verified by sequencing 44 of them. The enzyme FspBI correctly identified all investigated samples; the enzyme SspI identified all samples except one Cx. torrentium. We hope the method and the findings presented here will help to shed light on the true distribution and relative proportions of the two species in Europe.     

Comparison of the efficacy of CO2‐baited and unbaited light traps,gravid traps,backpack aspirators,and sweep net collections for sampling mosquitoes infected with Japanese encephalitis virus

Two field studies were conducted to determine the efficacy of mosquito collection methods for species composition, species abundance, and Japanese encephalitis virus infection rates in Taiwan. Traps evaluated included John W. Hock (JH) model UD black light traps, JH model 1012 new standard miniature CDC light traps, JH model 1712 CDC gravid traps, and Taiwan‐made Pest‐O‐Lite light traps. Backpack aspirators and sweep nets were also used to collect the resting population. Culex tritaeniorhynchus in all studies and Mansonia uniformis in the Taipei areas were the two most abundance species collected. Dry ice‐baited UD black light traps were effective in regard to species diversity, species abundance, and Japanese encephalitis virus infection rates. The unbaited Pest‐O‐Lite light traps collected significantly more female mosquitoes than the UD black light traps but performed similarly with regard to species diversity and male mosquito collection. Most mosquitoes collected by Pest‐O‐Lite light traps were dried and not suitable for virus detection. Dry ice‐baited CDC light traps collected significantly fewer mosquitoes than other light traps. Although CO₂‐baited UD black light traps with octenol attracted more mosquitoes, no statistical significance was found compared to CO₂‐baited UD black light traps without octenol. Japanese encephalitis viruses were isolated from half of the positive pools in UD black light traps and CDC light traps.     

Evaluation of collection methods for Culex quinquefasciatus,Aedes aegypti,and Aedes simpsoni in northeastern Tanzania

In East Africa, significant morbidity and mortality are caused by infections spread by Culex quinquefasciatus and Aedes aegypti. Sticky traps have been shown to be effective tools for sampling populations of Aedes mosquitoes and have been found to catch Cx. quinquefasciatus. Thus, they could potentially be used to sample populations of this species. This study compared Sticky ovitraps (SO) and MosquiTraps (MQT) with the CDC Gravid trap (CDC‐GT) for collection of Culex and Aedes mosquito populations in Tanzania. A follow‐up experiment was carried out using traps set for a 24‐h period to accommodate the oviposition habits of Aedes aegypti and Ae. simpsoni s.l. mosquitoes. The results showed that the CDC‐GT caught significantly more Cx. quinquefasciatus and Ae. aegypti than the SO or MQT, but there was no significant difference in the number of mosquitoes caught between the two sticky traps or of Ae. simpsoni s.l. caught among the three trap types. The results suggest that CDC‐GTs are the most appropriate in sampling of Cx. quinquefasciatus. Although CDC‐GTs collected more Ae. aegypti than the sticky traps, the simplicity and cost benefit of sticky traps facilitates large scale studies. All three trap types should be considered for monitoring Aedes mosquitoes.     

Improving efficacy of Box gravid traps for collecting Culex quinquefasciatus.

In outdoor screen cages, one and two-choice assays were conducted with gravid Cx. quinquefasciatus to assess and improve the efficacy of the Box gravid trap. Subsequently, in a field trial, a modified Box gravid trap was compared with three other gravid traps: the CDC gravid trap, the CFG gravid trap, and a novel design of a sticky gravid trap. A major disadvantage of the Box gravid trap, a relatively low trapping efficacy, was overcome with a simple modification to the trap configuration. By replacing the solid lid of the collecting tray with mosquito netting, the air velocity through the trap inlet was doubled and the quality of the resting sites for caught females was improved. As a result, the modified Box gravid trap caught and retained twice as many Cx. quinquefasciatus as its predecessor in two-choice bioassays in the screened cages and proved as effective as the commercially available CDC gravid trap in the field, but without damaging the collected specimens. Captures with the Box and CDC gravid traps were significantly greater than those of either the Counter Flow Geometry gravid trap or a sticky gravid trap.     

Field evaluation of baited traps for surveillance of Aedes japonicus japonicus in Switzerland

The efficacy of Centers for Disease Control (CDC) miniature light traps and ovitraps was tested in the outskirts of the city of Zurich in Switzerland for their use in the surveillance of Aedes (Hulecoeteomyia) japonicus japonicus (Theobald) (Diptera: Culicidae), the invasive Asian bush mosquito. Sets of single CDC traps were run overnight (n = 18) in three different environments (forest, suburban and urban) in 3 × 3 Latin square experimental designs. Traps were baited with: (a) carbon dioxide (CO₂); (b) CO₂ plus light, or (c) CO₂ plus lure blend [Combi FRC 3003 (iGu^®)]. At the same locations, mosquito eggs were collected weekly using standard ovitraps baited with different infusions (oak, hay or tap water) and equipped with different oviposition substrates (a block of extruded polystyrene, a germination paper strip or a wooden stick). Data were analysed using Poisson and negative binomial general linear models. The use of light (P < 0.001) or lure (P < 0.001) significantly increased the attractiveness of CDC traps baited with CO₂. Oak and hay infusions did not increase the attractiveness of ovitraps compared with standing tap water (P > 0.05), and extruded polystyrene blocks were preferred as an oviposition substrate over wooden sticks (P < 0.05) and seed germination paper (P < 0.05). Carbon dioxide‐baited CDC miniature light traps complemented with light or iGu^® lure and ovitraps containing standing tap water and polystyrene oviposition blocks can be considered as efficient and simple tools for use in Ae. j. japonicus surveillance programmes.     

A rural–urban latitudinal study of the distributions of Culex quinquefasciatus and Culex pipiens bioforms in their southernmost sympatric fringe

Mosquitoes grouped in the complex Culex pipiens L. (Diptera: Culicidae) are important vectors of medical and veterinary diseases. In the South American sympatric region, Cx. pipiens and Culex quinquefasciatus Say coexist and potentially hybridize. To identify key drivers of their geographical distribution, mosquito immatures were collected from flower vases of eight urban/rural cemetery pairs within a 5° latitudinal transect along Buenos Aires Province, Argentina. The specimens were identified by molecular methods and their relative proportion modelled as a function of environmental variables. At the beginning of the warm season, northern and southern cemeteries presented exclusively Cx. quinquefasciatus and Cx. pipiens, respectively, with different proportions of both at mid latitudes. By the end of the summer, Cx. quinquefasciatus was present throughout the study area, exclusively in 11 of the 16 cemeteries both rural and urban, whereas Cx. pipiens was predominant only in the southernmost pair. Mean annual temperature, photoperiod variability and time of the season were key drivers of their distributions. All specimens of Cx. pipiens were identified as form molestus and no hybrids were recognized. The reported distribution patterns and the potential absence of Cx. pipiens f. pipiens and hybrids are discussed, along with their implications in disease transmission.     

Mosquitoes of Western Yunnan Province,China: Seasonal Abundance,Diversity, and Arbovirus Associations

Objective

The western borderland between Yunnan Province, China, and Myanmar is characterized by a climate that facilitates year-round production of mosquitoes. Numerous mosquito-transmitted viruses, including Japanese encephalitis virus circulate in this area. This project was to describe seasonal patterns in mosquito species abundance and arbovirus activity in the mosquito populations.

Methods

Mosquitoes were collected in Mangshi and Ruili cities of Dehong Prefecture near the border of China and Burma in Yunnan Province, the Peoples Republic of China in 2010. We monitored mosquito species abundance for a 12-month period using ultraviolet light, carbon dioxide baited CDC light and gravid traps; and tested the captured mosquitoes for the presence of virus to evaluate mosquito-virus associations in rural/agricultural settings in the area.

Results

A total of 43 species of mosquitoes from seven genera were collected, including 15 Culex species, 15 Anopheles spp., four Aedes spp., three Armigeres spp., one Mimomyia spp., two Uranotaenia spp. and three Mansonia spp.. Species richness and diversity varied between Mangshi and Ruili. Culex tritaeniorhynchus, Culex quinquefasciatus, Anopheles sinensis and Anopheles peditaeniatus were the most abundant species in both sampling sites. Ultraviolet light traps collected more specimens than CDC light traps baited with dry ice, though both collected the same variety of mosquito species. The CDC gravid trap was the most effective trap for capture of Culex quinquefasciatus, a species underrepresented in light trap collections. A total of 26 virus strains were isolated, which included 13 strains of Japanese encephalitis virus, four strains of Getah virus, one strain of Oya virus, one strain from the orbivirus genus, and seven strains of Culex pipien pallens densovirus.

Conclusions

The present study illustrates the value of monitoring mosquito populations and mosquito-transmitted viruses year-round in areas where the climate supports year-round adult mosquito activity.     

Population Structure and Distribution Patterns of the Sibling Mosquito Species Culex pipiens and Culex torrentium (Diptera: Culicidae) Reveal Different Evolutionary Paths

Nowadays a number of endemic mosquito species are known to possess vector abilities for various diseases, as e.g. the sibling species Culex pipiens and Culex torrentium. Due to their morphological similarity, ecology, distribution and vector abilities, knowledge about these species'' population structure is essential. Culicidae from 25 different sampling sites were collected from March till October 2012. All analyses were performed with aligned cox1 sequences with a total length of 658 bp. Population structure as well as distribution patterns of both species were analysed using molecular methods and different statistical tests like distance based redundancy analysis (dbDRA), analysis of molecular variances (AMOVA) or McDonald & Kreitman test and Tajima''s D. Within both species, we could show a genetic variability among the cox1 fragment. The construction of haplotype networks revealed one dominating haplotype for Cx. pipiens, widely distributed within Germany and a more homogeneous pattern for Cx. torrentium. The low genetic differences within Cx. pipiens could be a result of an infection with Wolbachia which can induce a sweep through populations by passively taking the also maternally inherited mtDNA through the population, thereby reducing the mitochondrial diversity as an outcome of reproductive incompatibility. Pairwise population genetic differentiation (F_ST) ranged significantly from moderate to very great between populations of Cx. pipiens and Cx. torrentium. Analyses of molecular variances revealed for both species that the main genetic variability exists within the populations (Cx. pipiens [88.38%]; Cx. torrentium [66.54%]). Based on a distance based redundancy analysis geographical origin explained a small but significant part of the species'' genetic variation. Overall, the results confirm that Cx. pipiens and Cx. torrentium underlie different factors regarding their mitochondrial differentiation, which could be a result of endosymbiosis, dispersal between nearly located populations or human introduction.     

Influence of carbon dioxide on numbers of Culicoides midges collected with suction light traps in South Africa

To implement risk management against diseases transmitted by species of Culicoides Latreille, 1809 (Diptera: Ceratopogonidae), it is essential to identify all potential vectors. Light traps are the most commonly used tool for the collection of Culicoides midges. Given the indiscriminate artificial attraction of light, traps will collect all night‐flying insects rather than only livestock‐associated Culicoides midges. Factors that may increase the efficacy of traps, especially for livestock‐associated Culicoides midges, require investigation. In the present study, results obtained with Centers for Disease Control (CDC) and Onderstepoort light traps baited with carbon dioxide (CO₂) were compared with those of unbaited controls. Comparisons were made using two replicates of a 4 × 4 randomized Latin square design. With both trap types, the mean numbers of Culicoides midges collected in 16 baited traps were higher than those caught in 16 unbaited traps. Although exceptionally low numbers were collected with the CDC traps, the increases in the numbers and frequency of collection of Culicoides imicola Kieffer, 1913 were more pronounced in the CDC traps compared with the Onderstepoort traps. These results indicate that the addition of CO₂ may increase the efficiency of these traps for the collection of C. imicola and other livestock‐associated Culicoides species.     

The use of morphometric wing characters to discriminate female Culex pipiens and Culex torrentium

The reliability of the length of wing radial vein r_2/3 as a character for the morphological discrimination of the two potential arbovirus vectors Culex pipiens s.s. and Cx. torrentium from Germany was reassessed, after this character had been neglected for more than 40 years. Additionally, multivariate morphometric analyses were applied to evaluate wing shape variation between both species. Although high‐throughput molecular tools are now available to differentiate the two species, a simple, low‐cost routine alternative may be useful in the absence of a molecular laboratory, such as under semi‐field conditions. A thin‐plate splines transformation confirmed that primarily the shrinkage of vein r_2/3 is responsible for the wing differences between the two species. In the bivariate analysis, the r_2/3/r₃ indices of Cx. pipiens s.s. and Cx. torrentium were 0.185 and 0.289, respectively, resulting in a correct classification of more than 91% of all tested specimens. Using the absolute length of vein r_2/3 alone still allowed for more than 90% accurate discrimination. Furthermore, classification accuracy of linear discriminant analysis exceeded 97%.     

An unsettling explanation for the failure of skatole‐baited ovitraps to capture Culex mosquitoes

Culex mosquitoes are primarily found in temperate and tropical regions worldwide where they play a crucial role as main vectors of filarial worms and arboviruses. In Recife, a northeast city in Brazil, high densities of Culex quinquefasciatus are often found in association with human populated areas. In marked contrast to another part of the city, field tests conducted in the neighborhood of Sitio dos Pintos showed that trapping of mosquitoes in skatole-baited ovitraps did not differ significantly from captures in control (water) traps. Thus, classical and molecular taxonomic approaches were used to analyze the Culex species circulating in Sitio dos Pintos. Results obtained from both approaches agreed on the cocirculation of Culex quinquefasciatus and Culex nigripalpus in three different areas of this neighborhood. What was initially considered as an unexpected failure of this lure turned out to be a more unsettling problem, that is, the first report in Recife of Culex nigripalpus, a vector of Venezuelan equine encephalitis virus and West Nile virus. Unplanned urbanization processes close to remnants of the Atlantic forest, such as observed in Sitio dos Pintos, may have contributed to the introduction of Cx. nigripalpus in urban areas.     

Sympatric occurrence of Culex pipiens (Diptera,Culicidae) biotypes pipiens,molestus and their hybrids in Portugal,Western Europe: feeding patterns and habitat determinants

Culex (Culex) pipiens (Diptera: Culicidae) has two recognized biotypes, pipiens and molestus, which differ in physiology and behaviour; this difference may influence vectorial capacity for West Nile virus (WNV). Our goal was first to determine the presence of Cx. pipiens populations in 31 locations in Portugal and to subsequently analyse their host‐feeding preferences and habitat determinants. Molecular identification of Cx. pipiens forms and their hybrids was performed in 97 females; bloodmeal sources were identified in 59 engorged specimens. Overall, 61.9% of specimens were identified as Cx. pipiens f. pipiens, 20.6% as Cx. pipiens f. molestus, and 17.5% as hybrid forms. Culex pipiens f. pipiens fed preferentially on birds, and Cx. pipiens f. molestus on humans. Hybrid forms fed mostly on birds, but human bloodmeals were common. With reference to habitat, Cx. pipiens f. pipiens and hybrid forms were positively correlated with peri‐urban habitats. Our results confirm the sympatric presence of different Cx. pipiens biotypes in 14 of the 31 locations studied. Peri‐urban areas were a common habitat of all biotypes and may represent zones of hybridization. The feeding preferences and sympatric distribution of the Cx. pipiens biotypes observed in Portugal favour the epizootic circulation of WNV and the occurrence of disease outbreaks of WNV.     

Culex torrentium mosquitoes from Germany are negative for Wolbachia

Wolbachia (Rickettsiales: Anaplasmataceae) infects a wide range of arthropods, including several mosquito species. The bacterium is known to induce a plethora of phenotypes in its host, examples being the reproductive phenotype cytoplasmic incompatibility or resistance against infection with arboviruses. The latter is especially relevant when assessing the vector competence of mosquito species for emerging arboviruses. Thus, knowledge of Wolbachia infection status is important for the assessment of vector competence. To facilitate Wolbachia screening in mosquito populations, a quantitative polymerase chain reaction (qPCR) assay was developed to enable high‐throughput analysis of mosquito samples. Using this assay, the Wolbachia infection status of the two most common Culex mosquito species in Germany, Culex pipiens biotype pipiens Linnaeus (Diptera: Culicidae) and Culex torrentium Martini (Diptera: Culicidae), was assessed. About 93% of all tested C. pipiens biotype pipiens individuals were positive for Wolbachia, whereas none of the C. torrentium samples was found to be infected. Furthermore, other applications of the qPCR assay were explored by assessing a potential link between the levels of Wolbachia and West Nile virus (WNV) infections in German C. pipiens biotype pipiens mosquitoes. No relationship was found between the two variables, indicating that a Wolbachia‐induced antiviral phenotype in this mosquito population is not exclusively attributable to the general level of bacterial infection.     

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

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