Oviposition preferences of Culex restuans and Culex pipiens (Diptera: Culicidae) for selected infusions in oviposition traps and gravid traps

Field studies were conducted in southwestern Virginia to determine the ovipositional preferences of Culex restuans and Culex pipiens by using ovitraps and gravid traps baited with selected infusions. For the ovitrap collections, 4 different infusions (manure, hay, grass, and rabbit chow) were used. Significant differences among infusions were detected on most sample dates for both species. For 3 of the first 4 wk of collections, the manure infusion collected significantly more Cx. restuans than all the other infusions. The hay and grass infusions collected the majority of the egg rafts during weeks 5-9. Cx. pipiens egg rafts were absent from the first 3 wk of collections. Of the remaining 6 wk, 4 showed significant differences in attractiveness of infusions, with the hay and grass infusions preferred by Cx. pipiens. Two infusions, manure and hay, were used for the gravid trap experiment and both Cx. restuans and Cx. pipiens data were combined for analysis. Only the first 2 wk showed significance, with manure being preferred over hay in both weeks. In later collections, the relative attractiveness of the hay infusion increased. A seasonal shift in infusion preference may be related to incubation temperature during preparation of the infusions. New infusions were prepared each week and incubation was done outside. Increased attractiveness of the hay infusion coincided with higher average temperatures in July and August. Hay infusion was very effective for trapping both Cx. pipiens and Cx. restuans in southwestern Virginia and is more convenient to use than manure. However, cool outside temperatures in the early season may interfere with the fermentation process and thus incubation should be done for a longer time or brought indoors.     

Insemination rates of hybrids between Culex pipiens pipiens and Culex pipiens quinquefasciatus or Culex pipiens pallens at high temperature

Females of Culex pipiens pallens are rarely inseminated at temperatures above 30 degrees C. Insemination and egg-hatching rates (F2) were examined in females of hybrids (F1) between Culex pipiens pipiens and Culex pipiens quinquefasciatus at 25 degrees C and 30 degrees C to examine temperature-dependent reproductive activity. Insemination rates were very high in hybrid females (F1) at 25 degrees C and 30 degrees C, and egg-hatching rate (F2) also was high at both temperatures. Crosses between Cx. p. pipiens and Cx. p. quinquefasciatus did not show insemination rates and egg-hatching rates similar to the rates observed in Cx. p. pallens, suggesting that the hybrids expressed reproductive activity characteristic of Cx. p. quinquefasciatus.     

Redescription of the pupa of Culex restuans and a comparison with Culex nigripalpus

The pupa of Culex restuans is redescribed in detail with a chaetotaxal table and a full illustration. The chaetotaxy of the pupa of Cx. restuans is compared with that of Cx. nigripalpus, the primary vector of St. Louis encephalitis and West Nile virus in Florida.     

浦东国际机场致倦库蚊和淡色库蚊的调查研究

目的了解致倦库蚊和淡色库蚊在浦东机场的分布与活动规律。方法帐诱法、灯诱法、人诱法、捞勺法和人工小时法。结果致倦库蚊和淡色库蚊是浦东国际机场的优势蚊种,4-11月均有危害;灯诱法调查,季节消长呈坡型,蚊虫于4月出现,5-6月达到高峰,10-11月逐渐减少至消失;蚊虫活动（帐诱法）主要在晚上,黄昏时有群舞习性,活动高峰为日落后1～4h,白天基本不活动;刺叮（人诱法）高峰时间为21：00,叮人频率最高为42次/15min;入室蚊虫以19：00-22：00为多,入室率最高为9只/15min;幼虫主要孳生于池塘、水坑、洼地、下水道和容器等污染或干净的静止水体中。结论致倦库蚊和淡色库蚊是浦东国际机场危害人类的常见蚊种,其活动规律的研究对媒介控制和虫媒病的预警提供了技术支撑。     

Seasonal abundance and control of Culex spp. in catch basins in Illinois

Street catch basins in western Cook County, IL, were examined regularly June through August of 1987 to determine their seasonal larval production, adult mosquito harborage and the influence of abiotic factors on the associated mosquito population. Only larvae of Culex pipiens (63% of total) and Cx. restuans (37% of total) were recovered. These 2 species and Cx. erraticus were the most frequently collected adults. The abundance of mosquito larvae within catch basins was not correlated with water pH and only showed a weak, positive correlation with water temperature. Only a partial flushing of larvae (22-34% reduction) from catch basins by normal rainfall (less than 25 mm) was generally recorded. Treatments with larvicide oil (mineral seal oil/kerosene 175/tergitol) at a rate of 60-90 ml/catch basin resulted in a mean larval reduction of 97%. Adult females showed a mean reduction of 87%.     

Seasonal variation in populations of Anopheles maculipennis, Anopheles claviger and Culex pipiens in Turkey

Seasonal variation in larval populations of three species of mosquitoes, Anopheles maculipennis, An. claviger and Culex pipiens, common in the vicinity of Ankara, were studied. Populations of An. maculipennis and Cx. pipiens disappeared in larval habitats by December but An. claviger, overwintering as larvae remained until the middle of March. Animal footprints are densely populated and are preferred by Cx. pipiens and An. claviger over larger water bodies.     

Insecticide-resistance in Culex pipiens fatigans

The three main subspecies of the Culex pipiens complex—pipiens, fatigans and molestus—have similar “normal” levels of susceptibility to insecticides. C. p. fatigans larvae resemble those of anopheline mosquitos in sensitivity to dieldrin, but are more resistant to DDT; the adults are unusually resistant to chlorinated insecticides, but do not differ greatly from other species of mosquito in susceptibility to organophosphorus compounds.     

Is the Horaana strain of the Culex pipiens group Culex pipiens pallens?

The validity of the Horaana strain of the Culex pipiens group as Cx. pipiens pallens was studied. Judging from the fourth instar characters and morphology of the adult male genitalia, this laboratory strain is now out of the range of ordinary Cx.p. pallens in Japan, and must be identified as Cx. p. quinquefasciatus.     

Cane-sugar feeding in Culex pipiens fatigans

The relatively poor results that have been obtained in controlling or eradicating Culex pipiens fatigans, the urban vector of Wuchereria bancrofti, have made it necessary to obtain as much information as possible about its biology. In this paper the unexpected finding of the influence of cane sugar in delaying oviposition in the gravid female is reported. This is an important finding for those who are investigating the biology of this mosquito in the laboratory and who make use of the age-old practice of keeping adult mosquitos alive by feeding them cane sugar. It is also reported that under certain conditions extensive cane-sugar feeding takes place in nature and it seems possible that this habit may have unsuspected repercussions on behaviour and physiology beyond the confines of the laboratory. One possible development would be the isolation of the attractant present in unrefined sugars and its use in traps in order to assess mosquito populations in the field.     

Temperature-induced morphological change in Culex pipiens

The effect of temperature on Culex pipiens pipiens, Cx. p. quinquefasciatus, and reciprocal hybrids of the two was investigated by monitoring the DV/D ratios of these stocks maintained at 15.6 degrees C and 23.9 degrees C over 10 generations. Little variation occurred in mean values of the parental subspecies at either temperature. At 23.9 degrees C, the mean ratios for both hybrid lines rose from an intermediate value to a level well above the accepted minimum for Cx. p. quinquefasciatus (0.4), and the proportion of individuals identifiable as that subspecies increased 16-fold. At 15.6 degrees C, hybrid mean DV/D ratios decreased to or below the pipiens maximum value (0.2), and the proportion of pipiens individuals increased 4 to 5 times. The need to monitor closely the status of Cx. pipiens hybrid colonies is evident.     

Hybridization in the Culex pipiens complex

Studies of crosses of different strains of C. p. molestus in widely separated countries have given very similar results: crosses between certain combinations may be fully fertile or partly sterile.     

Unexpected spatiotemporal abundance of infected Culex restuans suggest a greater role as a West Nile virus vector for this native species

Difficulties in correctly differentiating Culex restuans mosquitoes from Culex pipiens have left the spatiotemporal mechanisms underlying the epidemiology of West Nile virus (WNV) in the northeastern United States largely unresolved. We performed weekly surveys across a natural to urban gradient of sites in central New Jersey (USA) and used a rapid and cheap DNA extraction and a species-specific PCR assay to create single species pools for WNV testing. To assess seasonal trends we combined these results with WNV surveillance records generated from grouped Cx. restuans/Cx. pipiens pools tested in 2011–2012. Cx. restuans was found to be highly abundant within all sites and reached especially high abundance in urban wetland habitats greatly disturbed by human action. In contrast, the seasonal presence of Cx. pipiens was greatest in residential and urban habitats and its presence in natural areas was minimal throughout the season. WNV infection rates in both species were similar but Cx. restuans was consistently found infected first and more frequently, even as early as May, whereas WNV was first detected in Cx. pipiens in late July. WNV activity peaked during the month of August when WNV was commonly isolated from both species. The peak in WNV activity in August observed for both species was consistent with data from 2011 to 2012 when Cx. restuans and Cx. pipiens were grouped, although analyzing single species pools increased overall predicted infection levels. Our results support the preeminence of Cx. restuans as an enzootic vector of WNV and strongly suggest this species has become a “native invasive” exploiting human modified habitats and reaching very high abundance there. Importantly, high infection rates in disturbed wetland sites with high populations of Cx. restuans suggest this species may enable the introduction of WNV to urbanized environments where both Culex contribute to transmission potentiating disease risk.     

The inheritance of yellow-larva and ruby-eye in Culex pipiens

It has been suggested that mosquito vectors of filariasis and other diseases might be controlled by genetic methods. This is not yet possible because of the lack of genetic information concerning the vector species. The present study describes the development of a marker strain which is being used to study genetic control.     

Development time, oviposition activity and onset of diapause in Culex tarsalis, Culex restuans and Culiseta inornata in southern Manitoba

Development times and survival of immatures and reproductive diapause of adult females of Culex tarsalis, Cx. restuans and Culiseta inornata were investigated from hatching to adult emergence at 15, 20 and 25 degrees C in the laboratory and at natural temperatures and photoperiods in southern Manitoba. Based on patterns of oviposition in artificial pools operated from mid-April to the end of September and development time of the immature stages, 3 generations of Cx. tarsalis, Cx. restuans and Cs. inornata were possible in 1980 and 1981. In 1981, 70% of field-reared Cx. tarsalis females emerging in mid-August were in diapause. Field-reared Cx. restuans and Cs. inornata entered reproductive diapause 2-3 weeks later than Cx. tarsalis.     

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.     

Occurrence and distribution of the Culex pipiens complex

Culex pipiens is the most widely distributed species of mosquito in the world, the typical form being found in temperate regions and the subspecies, fatigans, in the tropics. Fatigans is morphologically and biologically uniform in different geographical regions, whereas C. p. pipiens is very variable. Where the two forms come into contact, hybrid swarms occur. The only clear distinction between the two forms is in the nature of the male genitalia.