Nectar feeding by mosquitoes in Sweden, with special reference to Culex pipiens and Cx torrentium

1. Nectar feeding by mosquitoes collected from tansy (Tanacetum vulgare) flowers was studied in July and August 1983-85 at two sites in central and south-western Sweden. Prior to fructose analysis, gonotrophic state and parity was determined. 2. A total of 1010 mosquitoes (70% males) of eighteen species was collected. Fructose was detected in 75% of the males and 78% of the females. Most (86%) mosquitoes collected belonged to Culex pipiens and Cx torrentium. 3. Among 219 Cx pipiens females, for most of which the abdomen appeared gravid (52%) or empty (42%), 81% were fructose-positive. Females of other species were also proved to have fed on plant sugars in both early and later stages of the gonotrophic cycle. 4. In Cx pipiens and males of Cx torrentium peak nectar feeding occurred between 22.00 and 04.00 hours. Data for males of both species suggested a V-shaped pattern of nectar feeding activity during the night. 5. At about 16 degrees C nearly all mosquitoes became fructose-negative in the anthrone test within 20 h after collection from tansy flowers. 6. At least 44% of Cx pipiens females that were attracted to a dove-baited trap had fed on plant sugars shortly before.     

Blood meal analysis, flavivirus screening, and influence of meteorological variables on the dynamics of potential mosquito vectors of West Nile virus in northern Italy

An extended area of northern Italy has experienced several West Nile virus (WNV) outbreaks and the emergence of Usutu virus (USUV) during previous years. Our aim was to study some of the factors that could explain disease patterns in the Trentino region, where circulation was detected in human sera and sentinel chickens, but no human or equine cases were reported. We collected Culex species (Diptera: Culicidae) in peridomestic environments. The collected specimens were analyzed for feeding behavior, the influence of temperature and rainfall on the abundance of mosquitoes, and the occurrence of flaviviruses. Analysis of blood meals showed that Culex pipiens fed mainly on blackbirds (Turdus merula) and house sparrows (Passer domesticus), while Culex hortensis fed strictly on lizards. The abundance of Cx. pipiens females correlated positively with mean temperature and negatively with rainfall (one to four weeks before capture). This negative relationship could be due to the direct effect of the flushing of habitats together with an indirect effect of oviposition repellency. The mean weekly temperature influenced the abundance of Cx. hortensis. No flaviviruses were detected in the analyzed Culex mosquitoes. These data suggest a silent cycle at low enzootic transmission levels in the area. Furthermore, we present the first contribution to understanding the transmission role of Cx. pipiens mosquitoes in Italy by identifying vertebrate hosts to species level.     

Vector roles of Fennoscandian mosquitoes attracted to mammals, birds and frogs

1. Mosquitoes were sampled with five suction traps, from May to October 1983, at a forest site in south-central Sweden. 2. Twenty-three species of mosquitoes were identified among the total of 3108 females collected: 4% of them in an unbaited trap, 3% in a trap baited with two frogs, 24% with a guinea-pig, 28% with a hen and 40% in a trap baited with a rabbit. 3. The dominant species of Culicidae trapped were 39% Aedes communis (De Geer), 21% Ae. cinereus Meigen, 14% Coquillettidia richiardii (Ficalbi), 8% Ae. punctor (Kirby) and 4% Culiseta morsitans (Theobald). 4. Aedes annulipes (Meigen), Ae. cantans (Meigen), Ae. cinereus, Ae. communis and Ae. punctor were mostly attracted to the rabbit, whereas Culiseta morsitans, Culex pipiens L. and/or Cx torrentium Martini were strongly ornithophilic. 5. Based on these and previously published data the ecological and behavioural potential of the mosquitoes to transmit Sindbis, Inkoo, Tahyna and Batai viruses, tularaemia (caused by Francisella tularensis) and Ixodes-borne borreliosis (caused by Borrelia burgdorferi) in Fennoscandia is discussed. 6. The data support the hypothesis that Sindbis virus, which is enzootic in bird populations in Fennoscandia, is vectored between birds by Cx pipiens/torrentium and Cs. morsitans, and that abundant Aedes spp., particularly Ae. cinereus, which feed on both birds and mammals, are primary link vectors from infective birds to man and other mammals.     

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.     

Diel activity patterns of blood-seeking anthropophilic mosquitoes in central Sweden

1. Blood-seeking diel activity cycles of mosquitoes are described from 24 h landing catches on human bait in a field and a forest habitat during June-August in central Sweden. 2. Daytime activity in the field was low or absent, whilst in the forest activity was relatively even throughout the diel. 3. In both habitats, activity peaks generally occurred about sunset and sunrise and were more distinct in the field than in the forest. 4. Data from this and other studies show that, in general, Aedes cinereus Meigen feeds at night in field-type habitats and Ae.communis (DeGeer) during the diurnal-crepuscular period in forest and woodland habitats. 5. Although abundant in the study area, Anopheles maculipennis Meigen sensu lato, Culex pipiens L., Cx torrentium Martini and Culiseta morsitans (Theobald) were not caught on the human bait. This is because, in central Sweden, An.maculipennis s.l. is mainly feeding in animal sheds whereas the others are ornithophagous. 6. Ae.geniculatus (Olivier) was recorded from central Sweden for the first time. 7. Blood feeding success (proportion of mosquitoes that managed to obtain blood from the human bait) was significantly greater in Ae.cinereus (14.9%) than in Ae.punctor (Kirby), Ae.communis and Ae.annulipes (Meigen) (2.8-0.7%). 8. The data are interpreted in relation to the transmission of Ockelbo disease (caused by Sindbis virus) and tularaemia in Sweden.     

Physiological characteristics of Culex pipiens populations in the Middle East

We determined whether exposure to a short day-light regime of 14 h 15 min induces ovarian diapause in Culex pipiens L. mosquitoes from Israel and whether differences occur in certain morphological, physiological and behavioural traits. Samples from nineteen localities in Israel, from 33 degrees 05' N to 29 degrees 35' N latitude, conformed to the morphological criteria of Cx pipiens, sensu stricto (i.e. wider spread of dorsal than of ventral arms of the aedeagus) as determined by negative DV/D ratios of the male. Autogenous females occurred at frequencies of 4-55% in all areas of Israel throughout the breeding season. No mating barriers were detected between individuals of autogenous and anautogenous genotypes. Autogenous females were no more prevalent from polluted or enclosed breeding sites than from others with various degrees of openness. In general, Cx pipiens females fed equally well on human (35% engorgement) and avian (22% engorgement) hosts (P less than 0.01). Although females from the southern part of the study region appeared to be incapable of ovarian diapause, at least some of those from the north experienced diel-mediated diapause. We conclude that, in the Middle East, the 33rd parallel provides a southern limit to the range of Cx pipiens with capability for diel-mediated ovarian diapause, but that non-diapausing Cx pipiens s.l. are present at least as far south as Elat (20 degrees 25' N) on the coast of the Gulf of Aquaba.     

Effects of blood meal source on the reproduction of Culex pipiens quinquefasciatus (Diptera: Culicidae)

Culex pipiens quinquefasciatus were fed blood meals from a live chicken (LC), chicken blood in Alsever's (AC) solution, defibrinated bovine blood (DB), or bovine blood in citrate (CB) and incubated at 28° C. The effects of different blood meal sources were evaluated with respect to rates of blood feeding and reproduction (i.e., fecundity and fertility) over two gonotrophic cycles. Mosquitoes that fed on the first blood meal were subjected to a second blood meal as follows (first blood meal / second blood meal): LC/LC, LC/DB, DB/DB, CB/CB, AC/AC. Fecundity and fertility of Cx. p. quinquefasciatus were significantly (P < 0.05) greater in mosquitoes fed LC blood; however, fecundity and fertility in different treatment groups varied by gonotrophic cycle. These results contribute to our understanding of the impact of blood meal source on feeding and reproduction in Cx. p. quinquefasciatus. The potential impacts of blood meal source on virus transmission experiments are discussed.     

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.     

Seasonal prevalence of mosquitoes collected from light traps in the Republic of Korea, 2005

Adult mosquito surveillance was conducted during 2005 at 22 US military installations and two training sites located in six provinces in the Republic of Korea. Adult mosquitoes were collected in New Jersey light traps from 1 May to 15 October to determine threshold levels to initiate pesticide applications based on trap indices. A total of 27 363 adult mosquitoes (22 368 [81.7%] females and 4995 [18.3%] males) comprising 15 species (including five members of the Anopheles sinensis group) belonging to seven genera were collected. The most common species collected were members of the Anopheles sinensis Wiedemann group (50.2%), followed by Culex tritaeniorhynchus Giles (30.6%), Aedes vexans nipponii (Theobald) (11.8%), and Culex pipiens Coquillett (6.3%) females. Trap indices varied widely for species over their range, due in part to geographical distribution and degree of association with urban or rural communities.     

Preliminary report of knockdown resistance in Culex pipiens pallens and Aedes koreicus from Korea

Pyrethroid insecticides have been effective and powerful for controlling mosquitoes. However, abuse of these insecticides increases the number of resistant mosquitoes. In this study, Culex pipiens pallens and Aedes koreicus were collected from an artificial reservoir in the vicinity of a populated area in Korea, which is also a migratory bird catchment area. To monitor resistance to pyrethroid insecticides in mosquitoes, genomic DNA from the collected mosquitoes was sequenced for the kdr mutation in the voltage‐gated sodium channel (VGSC) gene. As a result, three samples with homozygous resistance (17.6%) and one with heterozygous resistance (5.9%) were found among 17 Cx. pipiens pallens specimens. One of the samples had a unique sequence at the amplified VGSC region. Of the 15 Ae. koreicus, no insecticide resistant individuals were found. In Korea, this is the first report of kdr genetic traits in Ae. koreicus and Cx. pipiens pallens and of a unique VGSC allele in Cx. pipiens pallens. Further investigation is needed to monitor the kdr resistance of these species in Korea and to determine how the unique sequence found in Cx. pipiens pallens is related to insecticide resistance.     

Detection and widespread distribution of sodium channel alleles characteristic of insecticide resistance in Culex pipiens complex mosquitoes in China

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.     

Seasonal prevalence of mosquitoes collected from light traps in the Republic of Korea, 2006

Adult mosquito surveillance was conducted during 2006 at 22 US Army and Air Force installations and two training sites located in six provinces in the Republic of Korea. Adult mosquitoes were collected in New Jersey light traps from 1 May through 15 October 2006 to determine threshold levels to initiate pesticide applications based on trap indices. In total 16 217 adult mosquitoes [13 612 (83.9%) females and 2605 (16.1%) males] comprising 16 species (including five members of the Anopheles sinensis Group) belonging to eight genera were collected. Females of the most commonly collected species were members of the Anopheles sinensis Wiedemann Group (58.9%), followed by Aedes vexans nipponii (Theobald) (21.3%), Culex tritaeniorhynchus Giles (11.8%) and Culex pipiens Coquillett (5.2%). Trap indices varied widely for species over their range, due in part, to their geographical distribution and degree of association with urban or rural communities.     

Emergence of Zika Virus in Culex tritaeniorhynchus and Anopheles sinensis Mosquitoes in China

Zika virus(ZIKV) has been isolated from mosquitoes such as Aedes, Mansonia uniformis, and Culex perfuscus; However,the isolation of ZIKV from Anopheles sinensis and Culex tritaeniorhynchus has not yet been reported. In June and July2018, 22,985 mosquitoes and 57,500 midges were collected in Jiangxi Province in southeastern China. Among them, six strains of ZIKV were isolated from mosquitoes: four from An. sinensis and two from Cx. tritaeniorhynchus. Molecular genetic analysis showed that the ZIKV isolated from An. sinensis and Cx. tritaeniorhynchus belonged to genotype 2 in the Asian evolutionary branch of ZIKV. In addition, the ZIKV strains isolated from An. sinensis and Cx. tritaeniorhynchus had amino acid substitutions identical to ZIKV strains prevalent in South America since 2015. This study is the first to isolate ZIKV from mosquito specimens collected in the wild of Jiangxi Province, China; This is also the first time that ZIKV has been isolated from An. sinensis and Cx. tritaeniorhynchus. Given that An. sinensis and Cx. tritaeniorhynchus have a very wide geographical distribution in China and even in eastern and southern Asia, the isolation of several strains of ZIKV from these two mosquitoes poses new challenges for the prevention and control of ZIKV infection in the mainland of China and countries and regions with the same distribution of mosquitoes.     

Potential vectors of West Nile virus following an equine disease outbreak in Italy

In the late summer of 1998, an outbreak of equine encephalomyelitis due to West Nile virus (WNV) occurred in the Tuscany region of central Italy. The disease was detected in 14 race horses from nine localities in four Provinces: Firenze, Lucca, Pisa and Pistoia. The outbreak area included Fucecchio wetlands (1800 ha), the largest inland marsh in Italy, and the adjacent hilly Cerbaie woodlands with farms breeding horses. To detect potential vectors of WNV, entomological surveys of Fucecchio and Cerbaie were undertaken during 1999-2002 by collecting mosquito larvae from breeding sites and adult mosquitoes by several methods of sampling. Among 6023 mosquitoes (Diptera: Culicidae) collected, 11 species were identified: Aedes albopictus (Skuse), Ae. vexans (Meigen), Anopheles atroparvus Van Thiel, An. maculipennis Meigen s.s., An. plumbeus Stephens, Culex impudicus Ficalbi, Cx. pipiens L., Culiseta longiareolata Macquart), Ochlerotatus caspius (Pallas), Oc. detritus (Haliday) and Oc. geniculatus (Olivier). In Fucecchio marshes, Cx. impudicus predominated with seasonal peak densities in spring and autumn: its greatest abundance during early spring coincides with arrival of migratory birds from Africa. In Cerbaie hills, Cx. pipiens predominated with peak population density in late summer. No viruses were isolated from 665 mosquitoes processed. These findings, plus other data on Italian mosquito bionomics, suggest a possible mode of WNV transmission involving the most abundant Culex in the Fucecchio-Cerbaie areas. Culex impudicus, being partly ornithophilic, might transmit WNV from migratory to non-migratory birds during springtime; Cx. pipiens, having a broader host range, would be more likely to transmit WNV from birds to horses and, perhaps, to humans by late summer.     

Effect of body size on energy reserves in Culex pipiens pallens females (Diptera: Culicidae)

We examined the relationship between body size and energy reserves of female Culex pipiens pallens under laboratory conditions. Small and large‐sized adult mosquitoes were obtained from larvae reared at different densities. There was a significantly positive relationship between pupal body weight and adult wing length depending on body sizes. Studies showed large females contained significantly higher contents of glycogen and lipid but lower protein stores in comparison to small females. Large sized mosquitoes accumulated higher percentages of glycogen (21.2% vs 15.9%) and lipid (45.8% vs 30.7%) but lower levels of protein (33.0% vs 53.4%) than small females. This result suggests that larval‐derived glycogen and lipid stores may be important in determining the body size of female Cx. pipiens pallens.     

A two-year survey on mosquitoes of Lebanon

A total of 6,500 mosquitoes were identified during a two-year survey (1999-2001) in Lebanon, and these belonged to twelve species: Culex pipiens, Cx. laticinctus, Cx. mimeticus, Cx. hortensis, Cx. judaicus, Aedes aegypti, Ae. cretinus, Ochlerotatus caspius, Oc. geniculatus, Oc. pulchritarsis, Culiseta longiareolata and Anopheles claviger. Culex pipiens was the most predominant species in Lebanon, collected indoors and outdoors. It was continuously abundant and active throughout the year. Culex judaicus was a small and rare mosquito and it is reported to occur for the first time in Lebanon. On the coastal areas, Ochlerotatus caspius was very common, and proved to be a complex of species as two forms were detected. One of the vectors of malaria, Anopheles claviger, was collected from May to September, from eight sites in Lebanon. Its breeding sites were restricted to fresh, cool, and clean water in pools and wells. Most of these breeding sites were in the populated Metn County where a few indigenous cases of malaria were reported from 1997-2000. This shows that the reported malaria cases were not imported, but caused by the bites of locally infected Anopheles females.     

The mosquito fauna of the western region of Spain with emphasis on ecological factors and the characterization of Culex pipiens forms

This study updates the diversity, distribution, and seasonal trends of mosquitoes in a western region of Spain, assesses ecological determinants of Culex pipiens s.l., and determines form composition of Cx. pipiens s.s. populations. A total of 1,495 mosquitoes of 16 species was collected during 2012–2013, of which Cx. pipiens s.l. and Cx. theileri were the most abundant. Five new records for An. maculipennis s.s., Orthopodomyia pulcripalpis, Aedes (Ochlerotatus) punctor, Cx. europaeus, and Cx. modestus were found for this region. Cx. pipiens density varied across weather and habitat patterns, correlating positively with high temperatures and with a preference for urbanized areas and rural areas within a proximity of ovine farms. Moreover, molecular identification by CQ11FL was performed in 467 Cx. pipiens s.s., detecting both pipiens (66%) and molestus (8.4%) forms coexisting in different habitats (urban, peri‐urban and rural) aboveground with a high degree of hybridization (25.7%). The abundance of Cx. pipiens in urban areas and farms, with the presence of hybrids, may increase their capacity to act as bridge vectors for the transmission of arboviral infections. These data will be helpful for further implementation of entomological programs focused on risk assessment for arboviruses or other mosquito‐borne pathogens.     

Differentiation between the urban mosquito Culex pipiens pipiens F. molestus and Culex torrentium (Diptera: Culicidae) by the molecular genetic methods

The molecular characters suitable for the differentiation between the autogenous form of Culex pipiens pipiens (the urban mosquito) and the species Culex torrentium, which was previously identified erroneously as an anautogenous form of C. pipiens pipiens (Shaikevich, Vinogradova, 2004), are given. These mosquitoes differ in the infection by the endosymbiotic bacteria Wolbachia pipientis, 6 transitions among 247 nucleotide sequences of 3' part of the cytochrome oxidase subunit I (COI) gene of mitochondrial DNA (mtDNA), in the mtDNA fragments resulted from the restriction analysis, and in the lengths of second internal transcribed spacer (ITS2) sequences in the ribosomal DNA.     

我国蚊虫体内感染的Wolbachia的wsp基因序列测定与分析

测定了我国尖音库蚊复合组和白纹伊蚊蚊虫体内感染的Wolbachia株的wsp基因序列。核苷酸和氨基酸的同源性及系统关系分析表明,我国尖音库蚊复合组和白纹伊蚊中Wolbachia株的wsp基因序列与Pip组其它株的核苷酸及氨基酸同源性分别为98%～100%和97%～100%, 属B大组Wolbachia中的Pip组。     

The 2000 epidemic of Rift Valley fever in Saudi Arabia: mosquito vector studies

In mid-September 2000, Rift Valley fever (RVF) virus was diagnosed as the cause of infection in humans and livestock in Jizan Region, Saudi Arabia. This is the first time that this arbovirus has been found outside Africa and Madagascar. Collections of mosquitoes (Diptera: Culicidae) were therefore undertaken (from 25 September to 10 October) at eight sites during the epidemic to obtain mosquitoes for attempted RVF virus isolation. Among 23 699 mosquito females tested, six isolations of RVF virus were made from 15 428 Culex (Culex) tritaeniorhynchus Giles and seven from 8091 Aedes (Aedimorphus) vexans arabiensis Patton [corrected]. Minimum mosquito infection rates per 1000 at sites with infected mosquitoes were 0.3-13.8 Cx. tritaeniorhynchus and 1.94-9.03 Ae. v. arabiensis. Viral activity moved northwards as collecting was in progress and collectors 'caught up' with the virus at the two most northerly sites on the last two trapping evenings. Other species occurred in small numbers and were identified but not tested. Both Cx. tritaeniorhynchus and Ae. v. arabiensis were susceptible to RVF virus and transmitted between hamsters, and an additional quantitative test with Cx. tritaeniorhynchus showed that 71-73% of mosquitoes became infected after ingesting 6.9-7.9 log10 FFU/mL of virus; transmission rates were 10% (post-infection day 14) and 26% (post-infection day 20). It was concluded that both species were vectors on grounds of abundance, distribution, preference for humans and sheep, the virus isolations and vector competence tests.