Prediction Forecast for Culex tritaeniorhynchus Populations in Korea

Objectives

Japanese encephalitis is considered as a secondary legal infectious disease in Korea and is transmitted by mosquitoes in the summer season. The purpose of this study was to predict the ratio of Culex tritaeniorhynchus to all the species of mosquitoes present in the study regions.

Methods

From 1999 to 2012, black light traps were installed in 10 regions in Korea (Busan, Gyeonggi, Gangwon, Chungbuk, Chungnam, Jeonbuk, Jeonnam, Gyeongbuk, Gyeongnam, and Jeju) to capture mosquitoes for identification and classification under a dissecting microscope. The number of mosquitoes captured/week was used to calculate its daily occurrence (mosquitoes/trap/night). To predict the characteristics of the mosquito population, an autoregressive model of order p (AR(p)) was used to execute the out-of-sample prediction and the in-sample estimation after presumption.

Results

Compared with the out-of-sample method, the sample-weighted regression method''s case was relatively superior for prediction, and this method predicted a decrease in the frequency of Cx. tritaeniorhynchus for 2013. However, the actual frequency of this species showed an increase in frequency. By contrast, the frequency rate of all the mosquitoes including Cx. tritaeniorhynchus gradually decreased.

Conclusion

The number of patients with Japanese encephalitis has been strongly associated with the occurrence and density of vector mosquitoes, and the importance of this infectious disease has been highlighted since 2010. The 2013 prediction indicated an increase after an initial decrease, although the ratio of the two mosquito species decreased. The increase in vector density may be due to changes in temperature and the environment. Thus, continuous prevalence prediction is warranted.     

Ingestion and development of Wuchereria bancrofti in Culex quinquefasciatus, Anopheles gambiae and Aedes aegypti after feeding on humans with varying densities of microfilariae in Tanzania

Laboratory observations were made on the transmission of Wuchereria bancrofti by Culex quinquefasciatus and Anopheles gambiae, natural vectors in East Africa, and by Aedes aegypti, an experimental vector. Mosquitoes were fed on human carriers with one to 2,667 microfilariae (mff/ml) of peripheral blood and the numbers of mff ingested were determined. The mosquitoes demonstrated a ‘concentrating effect’ and ingested 8.6 to 12-fold more mff than the expected number based on the density of mff in the carrier and the size of the blood meal. Studies on Culex showed that only 2.7 to 13% of the ingested mff developed into infective larvae (L3s). Emphasis was given to the transmission of Wuchereria from low density carriers with less than 10 mff/ml of peripheral blood—a value that approximates the threshold level of microfilaraemia detectable with conventional diagnostic techniques. By combining our laboratory data with published field data on the biting rates and longevity of mosquitoes in East Africa, we estimate that each low density carrier could serve as a source for nil to 15 L3s/year in Cx quinquefasciatus and 0.3 to 8 L3s/year in An. gambiae depending on the particular community. These estimates are relevant when formulating strategy to control bancroftian filariasis by mass chemotherapy with diethylcarbamazine. Experience with this drug has shown that a proportion of the carriers in a community continue to circulate mff at low levels after treatment. The present data demonstrate that these carriers serve as a reservoir of infection for mosquitoes.     

Ovicidal and Oviposition Deterrent Activities of Medicinal Plant Extracts Against Aedes aegypti L. and Culex quinquefasciatus Say Mosquitoes (Diptera: Culicidae)

Objectives

To evaluate the ovicidal and oviposition deterrent activities of five medicinal plant extracts namely Aegle marmelos (Linn.), Limonia acidissima (Linn.), Sphaeranthus indicus (Linn.), Sphaeranthus amaranthoides (burm.f), and Chromolaena odorata (Linn.) against Culex quinquefasciatus and Aedes aegypti mosquitoes. Three solvents, namely hexane, ethyl acetate, and methanol, were used for the preparation of extracts from each plant.

Methods

Four different concentrations—62.5 parts per million (ppm), 125 ppm, 250 ppm, and 500 ppm—were prepared using acetone and tested for ovicidal and oviposition deterrent activities. One-way analysis of variance (ANOVA) was used to determine the significance of the treatments and means were separated by Tukey''s test of comparison.

Results

Among the different extracts of the five plants screened, the hexane extract of L. acidissima recorded the highest ovicidal activity of 79.2% and 60% at 500 ppm concentration against the eggs of Cx. quinquefasciatus and Ae. aegypti, respectively. Similarly, the same hexane extract of L. acidissima showed 100% oviposition deterrent activity at all the tested concentrations against Cx. quinquefasciatus and Ae. aegypti adult females.

Conclusion

It is concluded that the hexane extract of L. acidissima could be used in an integrated mosquito management program.     

West Nile virus in Pakistan. III. Comparative vector capability of Culex tritaeniorhynchus and eight other species of mosquitoes

Eight species of mosquitoes from Pakistan were compared with Culex tritaeniorhynchus as experimental vectors of West Nile (WN) virus. When fed by the membrane or cotton-pledget methods on a dose of WN virus 100% infective for Cx tritaeniorhynchus, 95% and 73% of the females of Cx fuscocephala and Cx pseudovishnui became infected, respectively. Cx quinquefasciatus, Cx univittatus, Aedes albopictus, Ae. caspius, Ae. indicus and Ae. lineatopennis were all significantly less susceptible than Cx tritaeniorhynchus. In agreement with the single dose comparisons, the median per os infective dose of WN virus for Cx fuscocephala, Cx pseudovishnui and Ae. caspius was substantially greater than for Cx tritaeniorhynchus. The median parenteral infective dose for all six species tested was less than 1 SMICLD50. Both Cx tritaeniorhynchus and Cx quinquefasciatus were more susceptible to infection with WN virus when fed on viraemic chickens than when fed on defibrinated blood using cotton pledgets or membranes. After infection by intrathoracic inoculation, only Ae. indicus and Ae. lineatopennis showed a reduced ability to transmit WN virus when compared to Cx tritaeniorhynchus.     

Mosquitoes of the mangrove forests of India: Part 1--Bhitarkanika, Orissa

In this first paper of a series on mosquitoes of the mangrove forests of India, details of mosquito species recorded in Bhitarkanika, Orissa, are presented. Forty-three species of mosquitoes belonging to 21 subgenera and 13 genera, Aedes, Anopheles, Armigeres, Coquillettidia, Culex, Ficalbia, Heizmannia, Lutzia, Mansonia, Ochlerotatus, Toxorhynchites, Uranotaenia, and Verrallina, were recorded. Predominant larval habitat was the tree holes, from which 15 species were taken. Adults were mostly found resting in crab holes, tree holes, and hoof prints in the forest area and on walls in the guesthouse area. About 14 species were caught in light traps, while 19 species landed on humans for feeding. Ae. franciscoi and Oc. feegradei are 2 new country records for India. Ae. cancricomes and Cx. perplexus, known only from Andaman Islands of India, are new records for mainland India.     

The relationship between mosquito abundance and rice field density in the Republic of Korea

Background

Japanese encephalitis virus (JEV), the causative agent of Japanese encephalitis (JE), is endemic to the Republic of Korea (ROK) where unvaccinated United States (U.S.) military Service members, civilians and family members are stationed. The primary vector of the JEV in the ROK is Culex tritaeniorhynchus. The ecological relationship between Culex spp. and rice fields has been studied extensively; rice fields have been shown to increase the prevalence of Cx. tritaeniorhynchus. This research was conducted to determine if the quantification of rice field land cover surrounding U.S. military installations in the ROK should be used as a parameter in a larger risk model that predicts the abundance of Cx. tritaeniorhynchus populations. Mosquito data from the U.S. Forces Korea (USFK) mosquito surveillance program were used in this project. The average number of female Cx. tritaeniorhynchus collected per trap night for the months of August and September, 2002-2008, was calculated. Rice fields were manually digitized inside 1.5 km buffer zones surrounding U.S. military installations on high-resolution satellite images, and the proportion of rice fields was calculated for each buffer zone.

Results

Mosquito data collected from seventeen sample sites were analyzed for an association with the proportion of rice field land cover. Results demonstrated that the linear relationship between the proportion of rice fields and mosquito abundance was statistically significant (R² = 0.62, r =.79, F = 22.72, p < 0.001).

Conclusions

The analysis presented shows a statistically significant linear relationship between the two parameters, proportion of rice field land cover and log₁₀ of the average number of Cx. tritaeniorhynchus collected per trap night. The findings confirm that agricultural land cover should be included in future studies to develop JE risk prediction models for non-indigenous personnel living at military installations in the ROK.     

Food preferences and domiciliation of Culicidae mosquitoes in the Ribeira Valley, S?o Paulo, Brazil, with special reference to Aedes scapularis and Culex (Melanoconion)

New results on blood-meal identification and the environmental distribution of mosquitoes collected in four different Ribeira Valley (S. Paulo State, Brazil) environments, during the period February to November 1986, are presented. Sources of 651 blood-meals were identified. The preference of Ae. scapularis for large mammals, chiefly cattle, horse and even man, was confirmed. Data suggests that a similar behavioral pattern is presented by Cx. ribeirensis. Both mosquitoes seem to be strongly attracted by peridomiciliar blood sources represented by domestic animals sheltered in that environment. Nevertheless, the female of Ae. scapularis females may use the extradomiciliary environment, represented by residual forests, as resting place in the same way as it uses the peridomiciliary one. The data confirm the clear tendency of both Ae. scapularis and Cx. ribeirensis to adapt to the man-made environment and thus the evolution towards domiciliation in the behavior of these mosquitoes. Other culicids, such as An. bellator, An. cruzii and Cq. chrysonotum, were collected practically only by the use of human bait. For An. cruzii the number of females collected by this method represented 31.6% of the female total collected during this project. Some data about other species are given, and the need for further researches about Culex (Melanoconion) species is emphasized.     

Evaluation of the CDC gravid trap for the surveillance of St. Louis encephalitis vectors in Memphis, Tennessee

Collections with CDC Gravid Mosquito Traps on 954 trap-nights from May through September 1983 are compared to 2,608 concurrent resting site collections made in the same area of Memphis, Tennessee. Gravid Traps yielded 88 times more Culex per collection and 96 times more Culex per man hour. The total Gravid Trap catch was 135,724 mosquitoes, 99% of which were either Culex pipiens or Cx. restuans, whereas these species comprised only 63% of the 6,613 mosquitoes collected from resting sites. Gravid Traps also collected significant numbers of Aedes aegypti and Ae. triseriatus. On most nights, more than 95% of mosquitoes in the Gravid Trap catch were gravid females. These results demonstrate that the trap is an effective and efficient device for collecting several important vector species. The preponderance of gravid mosquitoes should enhance the probability of encountering pathogens acquired by blood-feeding.     

云南省蚊虫分布特点及自然感染乙型脑炎病毒的研究

目的分析云南省蚊虫分布特点及其与流行性乙型脑炎（乙脑）等虫媒病毒的关系,为防制提供依据。方法在云南省农村居民区住房、畜圈和野外竹林等生境捕蚊。结果采获成年雌蚊10属88种158909只,以库蚊、按蚊和伊蚊属蚊虫数量最多,分别占56．66％、25．35％和13．88％。在捕蚊总数中,居民区夜间捕获成蚊7属63种132081只,其中三带喙库蚊的构成比最高（42．12％）;其次为中华按蚊（23．31％）;野外白天捕获成蚊5属48种26828只,白纹伊蚊构成比最高（31．89％）,其次为圆斑伊蚊（20．21％）。对8属29种3957批131538只雌性成蚊进行病毒分离,结果从5属17种蚊虫体内分离到乙脑病毒81株,以库蚊分离出的毒株最多（59株）,占72．84％;其次为按蚊8株（9．88％）和伊蚊9株（占11．11％）;曼蚊和阿蚊均为2株（各占2．47％）。分离到乙脑病毒最多的蚊种为三带喙库蚊（27株）,占分离毒株总数的33．33％。结论居民区夜间活动蚊虫群落的优势种为三带喙库蚊、中华按蚊、棕头库蚊、霜背库蚊、伪杂鳞库蚊和迷走按蚊;野外白天活动蚊虫群落的优势种为白纹伊蚊、伪白纹伊蚊、圆斑伊蚊、骚扰阿蚊和刺扰伊蚊。三带喙库蚊和白纹伊蚊分别是云南省乙脑和登革热的丰要传播媒介。     

不同动物(血)对蚊虫的引诱作用

目的比较不同动物及动物血液对蚊虫的引诱作用,探讨蚊虫对动物宿主的嗜血习性。方法以不同动物血液引诱实验室饲养的蚊虫,以不同动物进行野外现场引诱蚊虫实验。结果实验室内淡色库蚊对猪血的吸血率最高,为51%,其他依次为人血、狗血、绵羊血和牛血;白纹伊蚊对牛血吸血率最高,为47%,其他依次为绵羊血、狗血、人血和猪血;埃及伊蚊对牛血吸血率也最高,为44%,其他依次为狗血、绵羊血、人血和猪血。现场实验表明家鸡对淡色库蚊引诱力较强,共诱集到1420只,其他依次为肉鸽、麻雀和大白鼠;家鸡对白纹伊蚊引诱力较强,共诱集到11只,其他依次为大白鼠、肉鸽和麻雀。结论淡色库蚊嗜吸猪血,白纹伊蚊、埃及伊蚊嗜吸牛血;家鸡对淡色库蚊的引诱效果较好。     

2006-2008年宁波市蚊虫季节消长调查与分析

目的 掌握宁波市蚊虫季节消长情况,为蚊虫防制提供科学依据.方法 采用人工小时法和灯诱法调查成蚊,定期观察积水容器蚊幼虫孳生情况.结果 2006-2008年室内共捕获成蚊7495只,密度指数为69.40只/人工小时,雌雄比为1:1.54;其中淡色库蚊占99.17%,白纹伊蚊、中华按蚊、三带喙库蚊分别占0.49%、0.20%、0.13%;成蚊密度高峰期分别为6-7月和10-11月.室内捕获栖息成蚊7886只,雌雄比为1:1.83;其中淡色库蚊占99.35%,白纹伊蚊、中华按蚊、三带喙库蚊分别占0.33%、0.14%和0.18%.城区放置诱蚊灯312个,捕获成蚊11 881只,雌雄比为1.09:1,平均密度指数为3.17只,(灯·h),公园、居民区、医院密度指数分别为6.27、2.10、1.16只/(灯·h),以公园密度指数最高;淡色库蚊为优势种,占90.60%,三带喙库蚊、白纹伊蚊、中华按蚊、其他蚊种分别占8.73%、0.36%、0.17%和0.14%;密度高峰期分别为6-7月和10-11月.农舍放置诱蚊灯71个,捕获成蚊3078只,雌雄比为4.76:1,平均密度指数为3.61只/(灯·h);三带喙库蚊为优势种,占73.91%,淡色库蚊、中华按蚊、白纹伊蚊分别占20.47%、3.54%、1.23%,其他蚊种占0.84%;密度高峰期为7-8月.采集幼虫(蛹)23 912条,平均1992.67条/个容器,白纹伊蚊、淡色库蚊分别占75.17%和24.42%,其他蚊种占0.41%;5-9月为密度高峰期.结论 宁波市蚊虫季节消长变化明显,要加强蚊虫孳生地的治理、灭蚊防蚊和疫苗接种工作,防治蚊媒传播疾病的发生.     

Oviposition signals and their neuroethological correlates in the Culex pipiens complex

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

The Risk of West Nile Virus Infection Is Associated with Combined Sewer Overflow Streams in Urban Atlanta,Georgia, USA

Background

At present, the factors favoring transmission and amplification of West Nile Virus (WNV) within urban environments are poorly understood. In urban Atlanta, Georgia, the highly polluted waters of streams affected by combined sewer overflow (CSO) represent significant habitats for the WNV mosquito vector Culex quinquefasciatus. However, their contribution to the risk of WNV infection in humans and birds remains unclear.

Objectives

Our goals were to describe and quantify the spatial distribution of WNV infection in mosquitoes, humans, and corvids, such as blue jays and American crows that are particularly susceptible to WNV infection, and to assess the relationship between WNV infection and proximity to CSO-affected streams in the city of Atlanta, Georgia.

Materials and methods

We applied spatial statistics to human, corvid, and mosquito WNV surveillance data from 2001 through 2007. Multimodel analysis was used to estimate associations of WNV infection in Cx. quinquefasciatus, humans, and dead corvids with selected risk factors including distance to CSO streams and catch basins, land cover, median household income, and housing characteristics.

Results

We found that WNV infection in mosquitoes, corvids, and humans was spatially clustered and statistically associated with CSO-affected streams. WNV infection in Cx. quinquefasciatus was significantly higher in CSO compared with non-CSO streams, and WNV infection rates among humans and corvids were significantly associated with proximity to CSO-affected streams, the extent of tree cover, and median household income.

Conclusions

Our study strongly suggests that CSO-affected streams are significant sources of Cx. quinquefasciatus mosquitoes that may facilitate WNV transmission to humans within urban environments. Our findings may have direct implications for the surveillance and control of WNV in other urban centers that continue to use CSO systems as a waste management practice.     

Frequency in human environment and dispersion of Culicidae mosquitoes in an area adjacent to a primitive Atlantic plain forest

Results of peridomiciliary and forest environment mosquito catches are presented. By using the method single host, mosquitoes were identified according to blood-meal and thus their dispersal was observed. Evidence was obtained for movements of Aedes scapularis, due apparently were appetential flights, as well as its permanence in peridomiciliar resting places. Occurrence in domestic animal shelters was recorded for this species. Peridomiciliar human bait catches showed regular occurrence of Ae. scapularis, Anopheles bellator, An. cruzii and Culex sacchettae, but anophelines abandoned the human environment for the surrounding forest. Feeding index showed clearly a preference on the part of Ae. scapularis for bovine hosts. The peridomiciliar frequency of Cx. sacchettae suggests a domiciliary tendency. The influence of large domestic animals in the human environment surrounded by primitive Atlantic plain forests, on the domiciliation of the sylvatic mosquitoes, is emphasized.     

Mosquito surveillance employing New Jersey light traps on Indian reservations in Iowa, Nebraska and South Dakota in 1984 and 1985

A mosquito surveillance program was established in 1983 on Indian reservations in Iowa, Nebraska and South Dakota. Standard New Jersey light traps were operated on 12 reservations throughout the summer seasons in 1984 and 1985. Rainfall levels in general were higher than normal at all sites in 1984 but were lower than normal at most sites in 1985. Aedes vexans was the most abundant species collected on all reservations and Culex tarsalis second in abundance. Man-biting collections of mosquitoes near Brookings in 1984 reached 35 mosquitoes/5 minutes in early July and were largely composed of Ae. vexans, Ae. dorsalis and Ae. nigromaculis while numbers of Cx. tarsalis and An. quadrimaculatus were minor. During the same period in 1985, man biting collections averaged less than 5/5 minutes.     

“Bird biting” mosquitoes and human disease: A review of the role of Culex pipiens complex mosquitoes in epidemiology

The transmission of vector-borne pathogens is greatly influenced by the ecology of their vector, which is in turn shaped by genetic ancestry, the environment, and the hosts that are fed on. One group of vectors, the mosquitoes in the Culex pipiens complex, play key roles in the transmission of a range of pathogens including several viruses such as West Nile and St. Louis encephalitis viruses, avian malaria (Plasmodium spp.), and filarial worms. The Cx. pipiens complex includes Culex pipiens pipiens with two forms, pipiens and molestus, Culex pipiens pallens, Culex quinquefasciatus, Culex australicus, and Culex globocoxitus. While several members of the complex have limited geographic distributions, Cx. pipienspipiens and Cx. quinquefasciatus are found in all known urban and sub-urban temperate and tropical regions, respectively, across the world, where they are often principal disease vectors. In addition, hybrids are common in areas of overlap. Although gaps in our knowledge still remain, the advent of genetic tools has greatly enhanced our understanding of the history of speciation, domestication, dispersal, and hybridization. We review the taxonomy, genetics, evolution, behavior, and ecology of members of the Cx. pipiens complex and their role in the transmission of medically important pathogens. The adaptation of Cx. pipiens complex mosquitoes to human-altered environments led to their global distribution through dispersal via humans and, combined with their mixed feeding patterns on birds and mammals (including humans), increased the transmission of several avian pathogens to humans. We highlight several unanswered questions that will increase our ability to control diseases transmitted by these mosquitoes.     

Shape relatedness between geographic populations of Culex tritaeniorhynchus,the primary vector of Japanese encephalitis virus: A landmark study

BackgroundJapanese encephalitis is a severe disease of acute encephalitis, with children and the elderly primarily affected, and with mortality rates reaching over 25%. The virus is transmitted mainly by species of the Culex (Culex) vishnui subgroup, primarily the widely spread Cx. tritaeniorhynchus Giles. The latter is known as a highly migratory mosquito which moves with airflow over large distances. We explored the geometric variation of the wing venation among distant areas of its geographic distribution. Our working hypothesis was that shape variation across geography could reveal known past and present migratory routes.Materials methodsWe compared the wing venation geometry of 236 female Culex tritaeniorhynchus from different locations in the Madagascan (La Reunion), Oriental (Thailand, Vietnam) and Paleartic (Japan) regions. To ascertain the taxonomic signal of the wing venation we also used two species as relative outgroups, Cx. whitmorei and Cx. brevipalpis.ResultsIn spite of an increasing morphometric variation as expected with larger geographic dispersion, our Cx. tritaeniorhynchus samples were clustered as a single species when considered relative to other Culex species. The relationships between geographic sites of Cx. tritaeniorhynchus globally conformed with an isolation by distance model. The shape homogeneity of our Palearctic samples (Japan) contrasted with some heterogeneity observed in the Oriental region (Thailand, Vietnam), and could be related to the different regimes of wind trajectories in these regions.ConclusionThe average shape variation of Culex tritaeniorhynchus disclosed a separation between Madagascan, Oriental and Palearctic regions in accordance with geography. The wing venation not only could reflect geography, it also contained a clear taxonomic signal separating three Culex species. Within Cx. tritaeniorhynchus, a contrasting pattern of shape variation between the Palearctic and the Oriental regions is tentatively explained by the influence of wind trajectories.     

Population genetics of the mosquito Culex pipiens pallens reveals sex-linked asymmetric introgression by Culex quinquefasciatus

The Culex pipiens complex in Asia includes a temperate subspecies, Culex pipiens pallens, of uncertain taxonomic status. The shape of the male genitalia suggests it is a hybrid between Cx. pipiens and Cx. quinquefasciatus. We studied populations of Cx. p. pallens in Japan, Korea, and China and compared them to local populations of Cx. quinquefasciatus and Cx. p. pipiens. We examined variation in a nuclear intron in the acetylcholinesterase-2 gene [ACE] and eight microsatellite loci. We found a distinct microsatellite signature for Cx. p. pallens indicating restricted gene flow between Eastern and Western populations of Cx. pipiens, supporting the existence of two subspecies. Furthermore, a multilocus genotype analysis revealed current hybridization between Cx. p. pallens and Cx. quinquefasciatus in southern Japan, Republic of Korea, and China but not in Hokkaido, in northern Japan. Surprisingly, however, we found that the sex-linked ACE locus in chromosome I has introgressed asymmetrically through the males such that all male Cx. p. pallens have a copy of the Cx. quinquefasciatus ACE locus. This result highlights some of the potential consequences of hybridization between local and introduced species to disease transmission worldwide.     

Bancroftian filariasis in coastal north Trinidad,West Indies: intensity of transmission by Culex quinquefasciatus

The intensity of transmission of Wuchereria bancrofti was measured in a coastal community in north Trinidad where 15% of the residents were microfilaraemic. The only significant vector, Culex quinquefasciatus, was studied in detail to determine seasonal abundance, longevity, infection and infectivity rates. Only 2·1% of the indoor biting population and 7·0% of the indoor resting population were infected. The daily mortality rate of the vector increased with age from 27% at four days to 44 to 47% at 12 days and is considered to be an important factor contributing to the low infectivity rate (0·1%). The mean number of C. quinquefasciatus bites received by a resident of the village during the year of observation was estimated to be 17,948 of which 14 were from mosquitoes harbouring infective larvae of W. Bancrofti. The results from similar studies elsewhere are outlined, but the need for standardization of procedures is emphasized before more reliable comparisons can be made.     

Comparison of four membranes for artificially bloodfeeding mosquitoes.

Four species of mosquitoes, Aedes aegypti, Ae. triseriatus, Culex pipiens and Cx. tarsalis, were allowed access to defibrinated rabbit blood via 4 different membranes and a standard membrane feeder. Natural animal skins (mouse or quail) were the most effective. More than 50% of the Aedes mosquitoes fed within 5 min and approximately 90% fed within 20 min on either mouse or quail skin. Culex species fed best on quail skin, but the difference in feeding on quail skin and sheep intestine was not significant at 10 or 20 min. In general Culex mosquitoes fed less readily on natural animal skins than Aedes.