Efficacy of gravid traps in trapping Culex pipiens

Members of the Culex pipiens complex are principal vectors for West Nile virus (WNV) in the USA. Previous studies have shown that gravid traps might be more effective than CO2-baited traps in sampling for Cx. pipiens. We compared the efficacy of gravid traps manufactured by 3 different companies: Bioquip, Clarke, and J. W. Hock. All gravid traps have a similar setup to hold the oviposition attractant but differ in the way they collect the mosquitoes. The gravid trap manufactured by J. W. Hock Company trapped significantly more Cx. pipiens than the other traps. Because CO2-baited American Biophysics Corporation (ABC) traps are most often used by mosquito abatement agencies, we compared the efficacy of the Hock gravid trap with a CO2-baited ABC trap. There was no significant difference in the number of Cx. pipiens trapped between the Hock gravid and CO2-baited ABC trap. Because gravid traps predominantly attract previously bloodfed females (thereby aiding in WNV surveillance) and are logistically easier and cheaper to set up, we argue that the Hock gravid trap might be ideal for sampling Cx. pipiens populations.     

淡色库蚊潜在的飞行能力

目的 淡色库蚊是班氏丝虫病的主要传播媒介,了解淡色库蚊的飞行行为,为淡色库蚊的防治提供科学依据.方法 采用吊飞技术对淡色库蚊实验室种群进行吊飞,设置为雌成虫1～10、15、20、25日龄,雄成虫为1～10日龄,每组至少10只试虫,采用单次最远飞行距离、单次最久飞行时间和单次最远飞行平均速度3项参数对不同性别淡色库蚊的飞行行为进行比较.结果 对淡色库蚊的成蚊吊飞研究发现,雌雄蚊的单次最远飞行距离差异无统计学意义(F=2.66,P=0.1044);淡色库蚊在各个日龄之间的单次最远飞行距离差异有统计学意义(F=2.15,P=0.0148);淡色库蚊性别和日龄的交互作用对单次最远飞行距离也有显著影响(F=2.00,P=0.0397);淡色库蚊雌虫各个日龄之间的单次最远飞行距离差异有统计学意义(F=2.42,P＜0.01);淡色库蚊雌蚊各日龄之间的单次最久飞行时间差异有统计学意义(F=2.91,P＜0.01);研究发现,淡色库蚊雌蚊羽化后的首次扩散距离高峰期(4日龄)、飞行能力低谷期(5、6日龄)、第2次扩散高峰期(7日龄)与雌蚊首次吸血高峰日龄、卵巢发育成熟的时间、卵发育成熟以后开始产卵的活动时间基本一致;雌虫羽化后7日龄的第2次扩散高峰期对确定雌蚊产卵范围有较大借鉴意义;雌蚊在20日龄的扩散能力峰值对确定班氏丝虫病传播过程中雌蚊的第2次吸血活动范围有重要参考意义.结论 淡色库蚊不同日龄之间的飞行能力有较明显差异,这种差异与淡色库蚊的生物学习性有较高的一致性,对指导班氏丝虫病的防控有较大的参考价值.     

Oviposition responses of gravid Culex quinquefasciatus and Culex tarsalis to bulrush (Schoenoplectus acutus) infusions

Laboratory bioassays demonstrated that fermented infusions of dried bulrushes (Schoenoplectus acutus) strongly attracted and stimulated oviposition by gravid female Culex quinquefasciatus and Culex tarsalis. The responses of the 2 species varied with the concentration and method of preparation of the infusions, with responses generally increasing with increasing concentration. No major differences were found in the responses of either species to infusions prepared with bulrushes alone, or with bulrushes plus lactalbumin hydrolysate and brewer's yeast. Infusions remained more attractive than distilled water controls to both species for up to 8 wk. Field tests corroborated the results from the laboratory bioassays. Culex quinquefasciatus, Cx. tarsalis, and Cx. stigmatosoma egg rafts were collected from water pan traps baited with bulrush infusions. A few Culiseta incidens eggs also were collected. In multiple-choice tests using gravid female or egg traps, Cx. quinquefasciatus preferred the most concentrated bulrush infusions, whereas Cx. tarsalis preferred intermediate concentrations. Female Cx. stigmatosoma and Culiseta incidens also were attracted. Overall, these results may provide new leads towards developing synthetic chemical baits to attract bloodfed mosquitoes.     

Attractiveness of selected oviposition substrates for gravid Culex tarsalis and Culex quinquefasciatus in California

Eight potential oviposition attractants were evaluated for gravid Culex tarsalis and Cx. quinquefasciatus under insectary, outdoor cage and field conditions. With the possible exception of a steer manure infusion under insectary conditions, none of the media consistently attracted large numbers of gravid Cx. tarsalis females. Reiter medium, steer manure infusion, cattle feces and Bermuda sod were attractive to gravid Cx. quinquefasciatus. Catch size at CDC gravid traps and oviposition traps were sensitive to the number of competitive oviposition sites and trap placement.     

Shelters of mosquitoes Culex (Culex) in rural zones (Diptera: Culicidae)

The human activities carried out in rural zones have been affecting the behavior of mosquitoes of the Culex (Culex) subgenera, which was the reason for undertaking this investigation with a view to registering data on the natural resting places in pastures and on the edge of or within primitive and residual forest areas. Three localities with different mesological conditions, as to type of human activity, all them situated in the Ribeira Valley region of S. Paulo State, Brazil, were chosen. The species most abundantly found were Cx. mollis (28.0%), Cx. declarator (25.0%), Cx. lygrus (13.0%) and Cx. coronator (9.6%). The collection of mosquitoes Cx. bidens + Cx. dolosus + Cx. chidesteri, known to be more urban, was much smaller than that of any other species of the group. With reference to outdoor environments, woodland contributed with 2,281 individuals (71.4%) suggesting their preference for this resting place, except for Cx. quinquefasciatus. Results are evaluated for the determination of the potential domicilation of each species and consequence of the same for the human population.     

Seasonal abundance of Culex restuans and Culex pipiens in southwestern Virginia through ovitrapping

Ovitrap collections were done to determine the seasonal distribution and ovipositional activity of Culex restuans and Culex pipiens in southwestern Virginia during summers 2002 and 2003. In both years, Cx. restuans was the first species collected and was the dominant species throughout the collecting period. More than 90% of the collections were comprised of Cx. restuans. Two oviposition peaks occurred in both years for Cx. restuans, the first in June and second in the middle of July. Culex pipiens made up less than 7% of the total catch and started to occur in the traps in the middle of the trapping season with a peak occurring in August. Although ovipositional activity began to decline for Cx. restuans, at the end of the trapping period, there was a slight increase in ovipositional activity for Cx. pipiens, but not enough to result in a crossover. A third species, Culex salinarius, was collected in the traps, but the total number of egg rafts accounted for less than 1% of the total collection.     

孑孓的龄期对武昌罗索线虫感染率的影响

在同一温度条件上，武昌罗索线虫寄生前期幼虫对致乏库蚊不同龄期幼虫的感染率均不相同。笔者分别对致乏库蚁Ⅰ、Ⅱ、Ⅲ、Ⅳ龄孑孓及蛹在２６±１℃条件下进行４８ｈ感染实验，感染率分别是５８．５％，７８％、６３．５％和１３．５％，以Ⅱ龄孑孓感染率最高，而蛹几乎不被感染。孑孓的龄期对寄生后期幼线虫雌、雄性比无明显规律性影响。     

Molecular and physiological characterization of the chitin synthase B gene isolated from Culex pipiens pallens (Diptera: Culicidae)

Human schistosomiasis is the second most important tropical disease and occurs in two forms in Africa (intestinal and urogenital) caused by the digenetic trematodes Schistosoma mansoni and Schistosoma haematobium, respectively. A proposed recent shift of schistosomiasis above a previously established altitudinal threshold of 1400 m above sea level in western Ugandan crater lakes has triggered more research interest there. Based on extensive field sampling in western Uganda and beyond and employing an approach using sequences of the mitochondrial barcoding gene cytochrome c oxidase subunit 1 (cox1) this study aims were: (i) identification and establishment of the phylogenetic affinities of Bulinus species as potential hosts for Schistosoma spp.; (ii) determining diversity, frequency and distribution patterns of Bulinus spp.; and (iii) establishing genetic variability and phylogeographical patterns using Bayesian inference and parsimony network analyses. Out of the 58 crater lakes surveyed, three species of Bulinus snails were found in 34 crater lakes. Bulinus tropicus was dominating, Bulinus forskalii was found in two lakes and Bulinus truncatus in one. The latter two species are unconfirmed potential hosts for S. haematobium in this region. However, Bulinus tropicus is an important species for schistosomiasis transmission in ruminants. Bulinus tropicus comprised 31 haplotypes while both B. forskalii and B. truncatus exhibited only a single haplotype in the crater lakes. All species clustered with most of the haplotypes from surrounding lake systems forming source regions for the colonization of the crater lakes. This first detailed malacological study of the crater lakes systems in western Uganda revealed presence of Bulinus species that are either not known or not regionally known to be hosts for S. haematobium, the causing agent of human urogenital schistosomiasis. Though this disease risk is almost negligible, the observed dominance of B. tropicus in the crater lakes shows that there is a likelihood of a high risk of infections with Schistosoma bovis. Thus, extra attention should be accorded to safeguard wild and domestic ruminants in this region as the population benefits from these animals.     

中华按蚊对3种细菌的产卵反应

目的具吸引作用的细菌或其挥发物能提高按蚊与杀虫或抗疟工程细菌接触的机会,为此,拟测定中华按蚊对A4细菌（未鉴定）、气单胞菌和肠杆菌的产卵反应特性,以明确3种细菌对中华按蚊是否具有吸引特性,为应用这3种细菌开展阻断疟疾传播研究提供理论和实验依据。方法已交配雌按蚊吸饱血48～60h后,将含不同细菌的滤纸产卵器放入蚊笼中供按蚊产卵。保持黑暗12h,待按蚊产卵后计数产卵器中按蚊卵的数量,应用成对t检验法比较中华按蚊在不同处理的产卵器中产卵量的差异。结果中华按蚊在含肠杆菌产卵器中的产卵量最多,在含A4菌和气单胞菌的产卵器中的产卵量明显低于对照和含肠杆菌的产卵器中的产卵量,P值分别为0.026、0.012、0.048和0.016;含肠杆菌的产卵器中的按蚊卵数量略高于对照,但差异无统计学意义（P〉0.05）。结论中华按蚊产卵时对A4菌和气单胞菌具有明显的负趋性,而对肠杆菌仅具有微弱的趋向性,推测这3种细菌可能不是中华按蚊食物的优先选择,但具有在蚊中肠内较为稳定存活的可能性,因此更适合于作为蚊幼生物杀虫基因的寄主细胞和仿转基因按蚊抗疟基因的寄主细胞被应用。     

Peroral susceptibility of Aedes albifasciatus and Culex pipiens complex mosquitoes (Diptera: Culicidae) from Argentina to western equine encephalitis virus

The transmission cycle of western equine encephalitis (WEE) virus in South America is unknown. A WEE virus strain was isolated from Aedes albifasciatus in Argentina during the WEE epizootic of 1982-83. Also, Culex pipiens from Argentina was reported to be able to transmit WEE virus experimentally, but other results indicate that Cx. pipiens from the USA is refractory to this virus. We determined the susceptibility of Argentina strains of Ae. albifasciatus and Culex pipiens complex mosquitos to infection by WEE virus by the oral route. Adult females were fed on chicks infected with a WEE virus strain isolated in Cordoba Province, Argentina, or were fed on a blood/virus suspension. Each mosquito ingested between 10(1.6) to 10(6.4) vero cell plaque-forming units of virus. Each of 28 Ae. albifasciatus was positive for virus from the fourth day postfeeding, and there was evidence for virus replication. In contrast, 0/44 Cx. p. quinquefasciatus and only 1/15 Cx. p. pipiens was positive. Aedes albifasciatus is susceptible to infection by WEE virus and should be considered a potential vector of this virus in Argentina. Both subspecies of Cx. pipiens are refractory to peroral infection by WEE virus and probably do not play a role in the WEE virus cycle in Argentina.     

糖和维生素对淡色库蚊及白纹伊蚊产卵选择的影响

目的评价不同营养物质对淡色库蚊和白纹伊蚊雌蚊产卵选择的影响,为新型诱卵器的研制提供理论支持。方法在室内测定淡色库蚊和白纹伊蚊对不同种类糖和维生素溶液的产卵趋性。结果淡色库蚊怀卵雌蚊偏好在1000mg/L和100mg/L浓度的葡萄糖溶液及1000mg/L浓度的蔗糖溶液中产卵,而白纹伊蚊则对供试的各种糖液没有明显的产卵选择偏好;浓度为100mg/L的盐酸硫胺（VB1）溶液和抗坏血酸（VC）溶液、10mg/L的VB1溶液能显著引诱淡色库蚊产卵,10mg/L的VB1溶液还能显著引诱白纹伊蚊产卵。结论葡萄糖对淡色库蚊、VB1对淡色库蚊和白纹伊蚊在室内有较好的产卵引诱效果。     

Discovery of Culex (Neoculex) arizonensis in Texas (Diptera,Culicidae)

A population of Culex arizonensis was found in Guadalupe Mountains National Park, Culberson County, TX. A new state record, this extends the range of this species eastward by 828 km. The essential diagnostic characters of the 4th-stage larva are given.     

Field and laboratory evaluations of potential oviposition attractants for Aedes albopictus (Diptera: Culicidae)

We tested five volatile synthetic chemicals (dimethyl disulfide, indole, 4-methylphenol, 3-methylindole, and trimethylamine) as potential oviposition attractants of Aedes albopictus in field and laboratory experiments. The 5 synthetic compounds were loaded into controlled-release packets, which consisted of a cellulose material sealed within a permeable plastic membrane, that were used to bait water-filled ovitraps at 5 field sites. Aedes albopictus exhibited no oviposition preference for any of the baited traps versus adjacent traps containing only water. In addition, there was no difference in the mean number of eggs laid per trap-day by Ae. albopictus among ovitraps treated with the five compounds. We conducted behavioral bioassays to determine if the lack of response to the putative oviposition chemicals in the field was due to a concentration effect. A binary sticky-screen bioassay was used to measure attraction of gravid females to olfactory stimuli. Compounds were evaluated over a range of concentrations that spanned 3-5 logs (0.0083 to 8.3 or 83 mg/liter). Three concentrations of 4-methylphenol (0.083 mg/liter, 0.83 mg/liter, and 8.3 mg/liter) and 1 concentration of 3-methylindole (8.3 mg/liter) were significantly repellent. All other concentrations of the 5 chemicals tested did not attract more females than did a water control. Electoantennography indicated that Ae. albopictus did not exhibit a physiological response to 0.25 ng of any of the five chemicals tested. Because Ae. albopictus did not exhibit attraction, greater oviposition. or an electrophysiological response to any of the compounds tested, these compounds do not appear to be effective lures for baiting ovitraps for surveillance or control of this mosquito.     

Time of arrival of gravid Culex pipiens fatigans at an oviposition site, the oviposition cycle and the relationship between time of feeding and time of oviposition

One of the most important activities in a female mosquito''s life is the flight to the breeding place and the subsequent deposition of eggs. During this phase, motivated by endogenous and exogenous stimuli, the female is particularly exposed and susceptible to attack. It is therefore important to investigate these episodes in the gravid female''s life.     

Effect of juvenile hormone and ecdysone on initiating blood meal--dependent vitellogenic ovarian cycles in autogenous and anautogenous Culex pipiens (Diptera : Culicidae)

The effect of juvenile hormone (JH) and ecdysone on initiating blood meal-stimulated ovarian cycles was studied in autogenous (2nd ovarian cycle) and anautogenous (1st ovarian cycle) Cx. pipiens. Although vitellogenesis was initiated in both mosquitoes in response to ecdysone, JHI and sequential JHI-ecdysone treatments induced vitellogenesis in anautogenous females only. JHI treatment initiated vitellogenesis in ca. 30% of anautogenous females and only half of those were able to form mature eggs. Sequential JHI-ecdysone treatment triggered vitellogenesis in 10 out of 25 anautogenous females and mature eggs were formed in three females only. In response to ecdysone, vitellogenesis in 10 out of 18 autogenous females and mature eggs were formed in two individuals. In ca. 70% of anautogenous siblings vitellogenesis was initiated and in most of those females mature eggs were developed. Our data suggests that differences in hormone-dependent events of vitellogenesis in autogenous and anautogenous Cx. pipiens seem to be related to the regulation of ecdysteroide release.     

蛋白质和氨基酸对2种蚊虫产卵选择的影响

目的评价不同蛋白质和氨基酸对我国2种重要媒介蚊虫淡色库蚊和白纹伊蚊雌蚊产卵选择的影响,为新型蚊虫诱卵器的研制提供理论支持。方法在室内测定淡色库蚊和白纹伊蚊对不同种类蛋白质和氨基酸溶液的产卵趋性。结果淡色库蚊怀卵雌蚊偏好在较高浓度的鱼蛋白胨溶液(1000和100mg/L)和酵母浸膏溶液(1000mg/L)中产卵,而10mg/L浓度的鱼蛋白胨溶液能显著引诱白纹伊蚊产卵;苯丙氨酸溶液在1000、100和10mg/L3个实验浓度下均能显著引诱淡色库蚊和白纹伊蚊产卵。结论鱼蛋白胨和苯丙氨酸对淡色库蚊和白纹伊蚊在室内有较好的产卵引诱效果。     

In vitro transmission of Wuchereria bancrofti L3-stage larvae by experimentally infected Culex pipiens L. (Diptera : Culicidae)

Females of Culex pipiens L. experimentally infected with Wuchereria bancrofti were tested for in vitro transmission of infective stage L3 larvae using a capillary tube technique. Of the females harbouring L3 larvae, 60.7% (34/56) transmitted a geometric mean of 2.84 L3 larvae (range 1-35). Transmitting Cx. pipiens contained significantly more L3 larvae than non-transmitters. Both the probability of transmission and the number of L3 larvae transmitted were related to the total number of loads larvae/mosquito. Almost all females with L3 loads > or = 10 transmitted larvae in vitro. The possibility is discussed that the detection of L3 larvae in field collected mosquitoes by dissection may overestimate the proportion capable of parasite transmission and the proportion of L3 larvae deposited on host skin by Ca. 40%.