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.     

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.     

Control of Aedes taeniorhynchus and Culex quinquefasciatus emergence with sustained release Altosid sand granules and pellets in saltwater and freshwater test plots.

The efficacy of sustained release Altosid sand granules to control adult Aedes taeniorhynchus and Culex quinquefasciatus emergence was investigated. Sand granules applied at a 7-day preflood application rate of 5.6 kg/ha controlled 99% of the Ae. taeniorhynchus emergence in saltwater plots for 44 days posttreatment and 35% of Cx. quinquefasciatus in freshwater plots. A 5.6 kg/ha rate controlled 100% of the Ae. taeniorhynchus emergence for 30 days posttreatment in semi-permanent saltwater plots. Altosid pellets were used at the label rate for comparison. Sand granules applied at 11.2, 16.8 and 22.4 kg/ha against Cx. quinquefasciatus in freshwater plots gave 98% emergence inhibition at the 22.4 kg/ha rate 37 days posttreatment, 93% at 16.8 kg/ha for 22 days, and 100% at 11.2 kg/ha rate for 16 days.     

Prey and size preference of Mesocyclops longisetus (Copepoda) for Aedes albopictus and Culex quinquefasciatus larvae

Laboratory studies investigated prey choice of the adult copepod Mesocyclops longisetus for Aedes albopictus and Culex quinquefasciatus larvae. Prey size preference by this predator was tested within and between instar classes at 10 and 30 degrees C. Single copepod adults preferred to prey on 1st and 2nd instars regardless of whether either species was alone or combined. Generally, M. longisetus preyed more on Ae. albopictus than on Cx. quinquefasciatus when similar larval stages were present. Also more prey of both species were consumed at 30 degrees C compared with 10 degrees C.     

The acetylcholinesterase gene Ace: a diagnostic marker for the Pipiens and Quinquefasciatus forms of the Culex pipiens complex

The taxonomy of the Culex pipiens complex remains a controversial issue in mosquito systematics. Based on morphologic characters, 2 allopatric taxa are recognized, namely Cx. pipiens (including the form "molestus") in temperate areas and Cx. quinquefasciatus in tropical areas. Here we report on variability at the nucleotide level of an acetylcholinesterase gene in several strains and natural populations of this species complex. Few polymorphisms were found in coding regions within a subspecies but many polymorphisms were observed between subspecies in noncoding regions. We describe a method based on a restriction enzyme polymorphism in polymerase chain reaction-amplified DNA, in which the presence or absence of one restriction site discriminates Cx. pipiens, Cx. quinquefasciatus, and their hybrids. This technique reliably discriminates mosquitoes from more than 30 worldwide strains or populations. Polymerase chain reaction amplification of specific alleles may also be a useful tool for characterizing specific alleles of each sibling taxon.     

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.     

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.     

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.     

Molecular and electron microscopic identification of Wolbachia in Culex pipiens complex populations from the Upper Rhine Valley, Germany, and Cebu City, Philippines

We detected Wolbachia infections in Culex pipiens complex mosquitoes from the Upper Rhine Valley, Germany, and Cebu City, Philippines, with the use of polymerase chain reaction (PCR) amplification of the 16S rDNA of the bacteria and further confirmation by electron microscopy. Species of 5 different autogenous and anautogenous populations of Culex pipiens from Germany and 1 population of Culex quinquefasciatus from the Philippines were used in this study. Larvae were sampled from different localities and reared to the adult stage for further processing. Whole adult males and the heads of adult females were processed by PCR, whereas the abdomens of females were used for electron microscopic study when an infection was detected by PCR. All Culex populations assayed by PCR showed infection of Wolbachia at rates between 10 and 100%. Females from different populations exhibited higher infection rates than did the males, and, likewise, Cx. pipiens populations that were autogenous showed higher infection rates of Wolbachia than did anautogenous individuals. In Cx. quinquefasciatus populations, males were infected at 33.33% and females, only 10%. We studied the ultrastructure of Wolbachia in the ovaries of species belonging to Cx. pipiens complex by means of transmission electron microscopy. The bacteria exhibited typical morphology for Wolbachia with 3 enveloping membranes.     

骚扰库蚊在我国新记录及其自育性和分类学研究

本文报告1992年在我国北京发现的骚扰库蚊亚种新记录,骚扰库蚊是孳生于不开放的地下水系中的自育性蚊种。实验室观察表明,其自育率在62%以上。雄蚊阳茎DV/D的比值在-0.0167～-0.125之间。阳茎形态和DV/D的比值与同属于尖音库蚊复合组的淡色库蚊亚种北京株存在很大的差异。     

Emergence patterns of Culex mosquitoes at an experimental constructed treatment wetland in southern California

The emergence patterns of mosquitoes inhabiting a 0.1-ha experimental wetland in southern California were monitored using emergence traps during the late summer and autumn of 1996. Culex erythrothorax was the largest contributor to emerging populations, comprising 94% of the total emerged adults with an average emergence rate of 59 adults/day/m2. None of the Culex species exhibited a pattern of emergence associated with water depth (range: 5-60 cm). Culex quinquefasciatus and Cx. tarsalis did not show a pattern of emergence associated with the inflow-outflow gradient; however, Cx. erythrothorax emerged in higher numbers along a transect at the middle of the wetland than from near the inflow and outflow. Additionally, the number of emerged Cx. erythrothorax was positively correlated with the density of vegetation below emergence traps. The comparatively large number of adults emerging from the middle of the wetland was most likely caused by a trade-off between an increasing gradient of resource abundance and a decreasing gradient of toxic compounds from the inflow to the outflow of the small wetland.     

淡色库蚊和致倦库蚊对杀虫剂抗药性的调查研究

目的 了解我国不同地区淡色库蚊和致倦库蚊对常用拟除虫菊酯类杀虫剂的抗性水平,为合理有效地使用化学杀虫剂提供依据.方法 采用滤纸接触筒法测定成蚊对10 000 mg/L溴氰菊酯和10 000 mg/L氯菊酯的1h击倒率和24 h死亡率.结果 北京市、河北和海南省淡色库蚊及致倦库蚊在溴氰菊酯和氯菊酯区分剂量下的24 h死亡率均＜80％,均为抗性种群.7株淡色库蚊对10 000 mg/L氯菊酯的24 h死亡率均＜50％;13株蚊虫对10 000 mg/L溴氰菊酯的抗性高低不一,24 h死亡率1％～66％不等.结论 北京市、河北及海南省淡色库蚊和致倦库蚊对拟除虫菊酯类杀虫剂均产生了高抗性,蚊虫抗药性的产生与杀虫剂的使用密切相关,在创建文明卫生城市工作中要科学合理用药,开展抗药性监测,采取适当措施延缓蚊虫抗药性的产生和发展.     

Vector competence of Culiseta incidens and Culex thriambus for West Nile virus

The vector competence of Culiseta incidens (Thomson) and Culex thriambus Dyar for West Nile virus (WNV) were compared to Cx. quinquefasciatus Say or Cx. tarsalis Coquillett and Cx. stigmatasoma Dyar collected concurrently in California. Culiseta incidens were less susceptible to oral infection than Cx. quinquefasciatus, but transmitted virus at a significantly higher rate, thereby yielding comparable population transmission rates. Culex thriambus was equally susceptible to oral infection and transmitted virus at rates comparable to Cx. tarsalis or Cx. stigmatosoma. A mammalian host selection pattern most likely precluded detection of natural infection in Cs. incidens, a fairly abundant peridomestic species. In contrast, an avian host selection pattern and efficient vector competence resulted in repeated detection of WNV in Cx. thriambus; however, limited abundance and restrictive riparian larval habitat requirements would seem to limit the involvement of Cx. thriambus in WNV epidemiology.     

Effectiveness and residual activity comparison of granular formulations of insect growth regulators pyriproxyfen and s-methoprene against Florida mosquitoes in laboratory and outdoor conditions

Effectiveness and residual activity tests of granular formulations of 2 insect growth regulators (IGRs), s-methoprene and pyriproxyfen, against laboratory-reared larvae of 5 colonized mosquitoes, Aedes aegypti, Aedes albopictus, Aedes taeniorhynchus, Anopheles quadrimaculatus, and Culex nigripalpus, were conducted in the laboratory and outdoors in plastic tubs. Culex quinquefasciatus was exposed to these two IGRs in the laboratory only. Each IGR formulation was applied at 0.02 and 0.05 ppm active ingredient (Al) against 5 of the 6 mosquito species both in the laboratory and the outdoor evaluations, whereas Cx. quinquefasciatus was exposed to 0.2 and 0.4 ppm AI of s-methoprene, and 0.1 and 0.2 ppm AI of pyriproxyfen in the laboratory. s-Methoprene at 0.02 and 0.05 ppm AI resulted in variable levels (<39-100%) of inhibition of adult emergence in the 5 species monitored for 6 weeks after treatment under both test conditions. Aedes taeniorhynchus was the most susceptible to s-methoprene in terms of initial and residual activity. Culex quinquefasciatus and Ae. albopictus were the most tolerant to s-methopene, with maximum emergence inhibitions amounting to 84% in Cx. quinquefasciatus at 0.4 ppm and 44.3% in Ae. albopictus at 0.05 ppm during the 1st week in the laboratory. Pyriproxyfen at comparable treatment rates to s-methoprene caused very high levels (>80-100% in most cases) of initial and residual emergence inhibitions of the tested species in the laboratory as well as outdoors. In several species, pyriproxyfen induced complete inhibition of adult emergence for several weeks after treatment, even at the lower rate of 0.02 ppm. The World Health Organization has recently recommended the use of pyriproxyfen for the control of some mosquito species at specified rates in certain habitats.     

Studies on the bioecological aspects of adult mosquitoes in the Prado Basin of southern California

Studies on the bionomics of adult mosquitoes were carried out in the Prado Basin of southern California during 1985-86. The faunal composition of mosquitoes caught by species was (in descending order) Culex quinquefasciatus, Cx. tarsalis, Cx. erythrothorax, Cx. stigmatosoma (formerly Culex peus) followed by Anopheles freeborni, Culiseta particeps, Cs. inornata and Cs. incidens. The number of mosquitoes per trap night was the lowest during December through February, and the highest during August through October. Depending on both intrinsic and extrinsic factors, adult mosquitoes were active at dusk and dawn. In spatial distribution studies, both adult and larval collections showed that Cx. quinquefasciatus and Cx. stigmatosoma were associated with dairy lagoons and Cx. erythrothorax with duck ponds and a nearby wooded area. Culex tarsalis was found in greater number at all habitats. Anopheles freeborni and Culiseta spp. were found around the wooded area. In vertical distribution studies, more mosquitoes were captured at the highest (6 m) level than at lower (0.6 and 3 m) levels which was probably due to the large percentage of parous females present at this site.     

Gonotrophic cycle and survivorship of Culex quinquefasciatus (Diptera: Culicidae) using sticky ovitraps in Monterrey, northeastern Mexico

Mark-release-recapture experiments were conducted to determine the length of the gonotrophic cycle and rate of survivorship of Culex quinquefasciatus Say in Monterrey, northeastern Mexico. A total of 2,352 field-caught Cx. quinquefasciatus females were marked and released at 8-12 h postemergence in 2 field trials. Sticky ovitraps were used to recapture marked gravid females. One hundred and ten (4.6%) marked females were recaptured during a 12-day sampling period. Recapture rates for the 2 individual trials were 6.4% and 3.5%. The length of the gonotrophic cycle, calculated as the average time between the initial blood meal and the time of recapture of gravid females, was 2-3 days. The first blood-fed mosquitoes were recaptured on the 2nd day postrelease. Gravid egg-laying females were most commonly recaptured at 2-3 days postfeeding. Daily survival estimates for the 2 release dates were of 0.871 and 0.883, respectively.     

A laboratory study of cyromazine on Aedes aegypti and Culex quinquefasciatus and its activity on selected predators of mosquito larvae

In a laboratory study, the insect growth regulator, cyromazine, exerted a high level of biological activity on Aedes aegypti and Culex quinquefasciatus treated in the 4th larval instar. At 1.5 and 1.0 ppm this IGR produced 97 and 99% inhibition of emergence in adult Ae. aegypti, respectively. In Cx. quinquefasciatus, there was 99% inhibition at 1 ppm and complete inhibition at 1.5 ppm. The overall pupal mortality was higher than larval or adult stages of both species. This material induced different types of morphogenetic abnormalities in pupae and adults of the 2 species similar to those induced by other IGRs. However, most abnormalities were observed in the pupal stage. Adverse effects were not detected on the 4 mosquito predator species during the acute or posttreatment tests.     

Effectiveness of five methods for sampling adult Culex mosquitoes in rural and urban habitats in San Bernardino County, California

The comparative effectiveness of NJ light traps, CO2-baited traps, walk-in red boxes, high-intensity light traps and gravid traps for sampling adult Culex mosquitoes for arbovirus surveillance was compared at rural dairy and residential urban habitats near Chino, California. Culex quinquefasciatus was the most abundant of the 3 species present comprising 94.9% of the 23,159 mosquitoes collected, followed by Cx. peus (4.2%) and Cx. tarsalis (0.9%). Female mosquitoes of all species were most abundant in CO2-baited traps at both urban and rural environments. Males were collected most effectively by walk-in red boxes in rural, but not urban, environments. More parous females were collected by CO2-baited traps at urban than rural habitats; however, 70-79% of all females were nulliparous and had never blood fed. These data point out the potential insensitivity of the current sampling methodology in monitoring mosquito arbovirus infection rates.     

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.