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.     

Evaluation of oviposition substrates and organic infusions on collection of Culex in Florida

Gravid mosquito traps are commonly used for both arbovirus surveillance and population surveillance of mosquitoes of the genus Culex. Oviposition substrates, used as baits in these traps, were tested against Culex under laboratory and field conditions. In the laboratory all substrates tested as 1% and 10% dilutions in 2-choice bioassays against female Cx. quinquefasciatus were significantly more effective than well water controls in eliciting oviposition. Strongest responses were to dilutions of dairy effluent, followed by larval water and infusions of alfalfa hay, alfalfa pellets, Bermuda hay, oak leaves, and Typha leaves, with lowest responses to cow manure infusion. In the field, few significant differences in collections were obtained between traps baited with different infusions. Significantly more Cx. quinquefasciatus and Cx. nigripalpus were collected in traps baited with cow manure infusion (highest) compared to alfalfa hay infusion (lowest). Responses of Cx. quinquefasciatus to dairy effluent and infusions of Bermuda hay, oak leaves, and Typha leaves were not significantly different from either cow manure infusion or alfalfa hay infusion. Responses of Cx. nigripalpus were highest to cow manure infusion and equally low to infusions of alfalfa hay and Typha leaves; moderate responses were observed to dairy effluent and infusions of Bermuda hay and oak leaves. Gravid females comprised 66.7-81.9% of the collections for each infusion type, with no significant difference among infusions in the proportion of gravid females collected.     

Field comparison of Bermuda-hay infusion to infusions of emergent aquatic vegetation for collecting female mosquitoes

Field experiments were conducted in east-central Alabama in 2003 and 2004 to compare the attractiveness of selected gravid-trap infusions to ovipositing female mosquitoes. Comparisons were made among infusions of the following plants: Bermuda hay, Cynodon dactylon, and 3 species of emergent aquatic plants typical of Culex larval habitats, i.e., soft rush, Juncus effusus; a common sedge, Rhynchospora corniculata; and broad-leaf cattail, Typha latifolia. Experiments were conducted at a site in Lee County, AL, with an abundance of common nuisance mosquitoes, including Culex quinquefasciatus and Aedes albopictus. Carbon dioxide-baited miniature light traps were operated concurrently with gravid traps to provide an activity index of mosquito species at the site. Gravid traps with hay infusion collected the greatest numbers of Cx. quinquefasciatus and Culex restuans females (2003). The results indicate that hay infusion is highly attractive to Cx. quinquefasciatus and is the infusion of choice for collecting females of this species in gravid traps. In the case of Ae. albopictus, infusions were not determined to be significantly different from one another in their attractiveness to gravid females. In general, females of Cx. quinquefasciatus and Cx. restuans demonstrated selectivity when choosing an oviposition site, whereas Ae. albopictus females did not. Factors associated with the oviposition biology of the latter species most likely account for their lack of preference for any single infusion type.     

Comparison of infusions of commercially available garden products for collection of container-breeding mosquitoes

In 2004, gravid-trap infusions made from commercially available garden products were compared in field assays to determine their attractiveness to ovipositing female mosquitoes. Experiments were conducted simultaneously at a residential site and at an auto salvage yard in Lee County, AL, each site having an abundance of container-breeding mosquitoes. Several infusion types were initially screened, from which the following 4 infusions were selected to be compared using gravid traps for their attractiveness to mosquitoes under field conditions: oak leaves, pine straw, red (dyed) hardwood mulch, and composted manure. Culex quinquefasciatus was the only species collected in greater numbers with gravid traps than with light traps, and the difference was more than 5-fold at both study sites. Gravid traps collected (mean +/- SD) 3.1 +/- 4.3 and 6.9 +/- 11.5 Cx. quinquefasciatus females at the residential and auto salvage sites, respectively. The response of Cx. quinquefasciatus females to infusions tested was variable, and no single infusion was consistently more attractive throughout the experiment. Gravid traps collected 1.7 +/- 1.9 and 4.7 +/- 4.4 Aedes albopictus females, 0.3 +/- 1.4 and 0.5 +/- 1.3 Cx. nigripalpus females, and 0.3 +/- 0.9 and 0.2 +/- 0.8 Cx. restuans females at the residential and auto salvage sites, respectively. Roughly 5-, 20- and 10-fold the numbers of females of Aedes albopictus, Cx. nigripalpus, and Cx. restuans were collected by light traps than by gravid traps at both sites. Aedes albopictus females did not demonstrate a preference for any of the infusions tested. Significant difference among infusions for Cx. restuans and Cx. nigripalpus were detected on just 1 trap-night. On this occasion, traps with red (dyed) hardwood mulch collected significantly more females of Cx. restuans and Cx. nigripalpus than did traps with other infusions. This work indicates that gravid traps are effective tools for collecting Cx. quinquefasciatus females, and a wide variety of organic materials may be used to produce infusions that can be used to attract ovipositing container-breeding mosquitoes.     

Comparison of mosquito trapping method efficacy for West Nile virus surveillance in New Mexico

As part of the West Nile virus surveillance program for the state of New Mexico, 13 sites along the Rio Grande River were sampled for mosquitoes during spring and summer 2003. We evaluated 3 different trapping procedures for their effectiveness at capturing selected species of mosquitoes. The 3 methods used were a dry ice-baited Centers for Disease Control and Prevention (CDC) light trap set 1.5 m above the ground (standard method), a CDC light trap suspended within the forest canopy, and a gravid trap set on the ground. Thirteen sites were sampled for 10 1-night periods biweekly from May through September. The relative numbers of captured Culex tarsalis, Cx. salinarius, Cx. quinquefasciatus, and Aedes vexans as well as the numbers of total recorded captures of all species were compared for each trapping method. Significant differences were observed for each species by location and by trapping method. Culex tarsalis was most commonly caught in canopy or standard CDC traps, especially in cottonwood bosque. Culex salinarius was found most frequently in association with marshy water, and was most often caught in gravid or standard light traps. Culex quinquefasciatus was captured almost exclusively in gravid traps within urban areas. Aedes vexans was primarily sampled in standard CDC light traps and found most frequently in wooded areas near floodplains. With the exception of Cx. Quinquefasciatus, no species was collected significantly more frequently in gravid or canopy traps than in the standard CDC light trap. Our findings do not support altering the methods currently used in New Mexico, namely, the use of 1.5-m CDC light traps and gravid traps. An increased use of gravid traps seems to be warranted in monitoring urban vector populations (specifically Cx. quinquefasciatus and Cx. salinarius) that may be involved in human transmission.     

Urbanization and the efficiency of carbon dioxide and gravid traps for sampling Culex quinquefasciatus.

The efficiency of gravid and CO2 traps for sampling female Culex quinquefasciatus was evaluated along 2 parallel 6.4 km long urban (high housing density) to rural (low housing density) transects in east Bakersfield, Kern County, CA. There were no significant differences in the number of female Cx. quinquefasciatus collected by gravid traps within urban and rural zones. The number of females collected per trap night ranged from 6.8 to 15.5. The number of females collected by CO2 traps increased significantly from 1.4 to 3.1 per trap night in urban to 31.8 to 111.2 per trap night in rural zones and was inversely correlated with housing density. These results indicate that female Cx. quinquefasciatus were effectively sampled by gravid traps in urban subdivisions and by CO2 traps in rural mixed agricultural areas.     

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.     

Comparison of engorged Culex quinquefasciatus collection and blood-feeding pattern among four mosquito collection methods in Puerto Barrios, Guatemala, 2007

Investigators have used a variety of techniques to sample resting, engorged mosquitoes for the purposes of studying mosquito blood-feeding behavior. However, evidence exists that mosquito blood-feeding patterns may vary according to collection method. Engorged mosquitoes were collected from rural and urban habitats after the 2007 dry (July) and wet (December) seasons in the Department of Izabal, Guatemala, with the use of Centers for Disease Control and Prevention (CDC) light traps, gravid traps, and aspiration from plastic pots and vegetation. We evaluated the utility of plastic pots as sampling tools for engorged Culex mosquitoes and compared Cx. quinquefasciatus blood host identities among collection methods. The array of vertebrate hosts supplying blood to Cx. quinquefasciatus did not differ significantly by method of collection. The density of engorged Cx. quinquefasciatus per trap-night was not significantly different between CDC light traps, gravid traps, and plastic pots; however, there was a significantly higher proportion of total mosquitoes that were engorged collected from pots than from either CDC light traps or gravid traps.     

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.     

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.     

Commercial mosquito trap and gravid trap oviposition media evaluation, Atlanta, Georgia

Field trials evaluating the effectiveness of selected gravid trap oviposition media and commercially available mosquito traps were conducted in southern Fulton County (Atlanta), GA, from June 9 to June 18 and June 24 to July 4, 2002, respectively. Total number of mosquitoes and number of each species captured during the tests were compared using a Latin square design. For the gravid trap infusion media, significant differences were found for total number of mosquitoes collected where sod > or = hay > or = hay side-by-side diluted hay > dilute hay side-by-side hay > or = oak > diluted hay. Only Aedes albopictus (oak), Culex quinquefasciatus (sod and both concentrated hay infusions), and Culex restuans (sod) were captured in significantly greater numbers using a particular infusion. Significant differences for the total number of mosquitoes collected were also observed in the commercial mosquito traps such that the gravid trap > ultra violet up-draft > or = Mosquito Magnet Pro > or = omnidirectional Fay-Prince trap with CO2 > up-draft CDC-style with CO2 > or = CDC-style with CO2. Significant differences in numbers collected among traps were noted for several species, including Aedes vexans, Aedes albopictus, Cx. quinquefasciatus, Cx. restuans, and Culex salinarius. Results from these field trap and infusion evaluations can enhance current surveillance efforts, especially for the primary vectors of West Nile virus and other arboviruses.     

Development time of Culex mosquitoes in stormwater management structures in California

A widely recommended strategy to minimize mosquito production in structural stormwater Best Management Practices (BMPs) is to ensure they hold captured water for no more than 72 h. However, this standard may be overly conservative for many mosquito species found in urban environments and may impede or prevent the capacity of BMPs to fulfill more stringent water quality standards in environmentally sensitive areas. Egg-to-pupa development of Culex tarsalis, Cx. pipiens, and Cx. quinquefasciatus were examined during July, August, and September 2006 in stormwater management basins and in water collected from these basins in 3 climatically distinct regions of California: the Lake Tahoe Basin, Sacramento Valley, and Los Angeles Basin. The observed minimum times to pupal development were 6 days for Cx. tarsalis and Cx. quinquefasciatus and 8 days for Cx. pipiens. Multiple linear regression models were used to estimate minimum predicted development times under optimal conditions for each region. The results suggest that water residence times of up to 96 h will not significantly increase the potential for Culex mosquito production in stormwater BMPs in the 3 regions included in this study.     

Entomologic studies after a St. Louis encephalitis epidemic in Grand Junction, Colorado

In 1986, after a St. Louis encephalitis epidemic in Grand Junction, Colorado, in 1985, vector mosquitoes in the city were surveyed to correlate their bionomics and infection rates with the occurrence of human disease. No human cases were reported, but mosquito surveillance disclosed St. Louis encephalitis virus in Culex tarsalis and Culex pipiens pipiens. Mosquitoes were collected with gravid traps designed to attract Cx. p. pipiens and with Centers for Disease Control light traps. Culex p. pipiens was the predominant vector mosquito collected and was captured chiefly in gravid traps. The Culex tarsalis population emerged and expanded approximately one month earlier than did the Cx. p. pipiens population. Consequently, Cx. p. pipiens was the predominant vector species after August. Infection rates throughout the surveillance period (June to September) were severalfold higher in Cx. tarsalis than in Cx. p. pipiens; however, in late summer, diminished numbers of Cx. tarsalis and a persistent population of Cx. p. pipiens resulted in relatively larger numbers of infected Cx. p. pipiens. Thus, the participation of Cx. p. pipiens as a St. Louis encephalitis vector would have been underestimated in previous studies employing light traps alone. These studies provide further evidence that Cx. p. pipiens-associated urban St. Louis encephalitis and rural Cx. tarsalis-associated St. Louis encephalitis cycles may coexist in the West.     

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.     

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。     

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.     

Comparative effectiveness of three adult mosquito sampling methods in habitats representative of four different biomes of California.

The effectiveness of New Jersey (NJ) light, dry ice baited, and gravid female traps for collecting adult mosquitoes was compared at representative habitats in the Coachella, San Joaquin, and Sacramento valleys and the Los Angeles basin of California. The NJ light traps effectively sampled Anopheles freeborni, Culex tarsalis, Psorophora columbiae, and several Aedes when abundance was high in rural areas with minimal competitive illumination. Dry ice-baited encephalitis virus surveillance or CDC style traps collected significantly more females of most species at most localities than did NJ light traps, regardless of background illumination. The Cummings modification of the Reiter gravid female trap baited with a bulrush (Schoenoplectus) infusion was the best method for collecting Culex pipiens complex females in most habitats. In the Los Angeles basin, gravid traps baited with bulrush infusion collected, on average, 4.5 times more Culex quinquefasciatus females than did traps baited with the Reiter infusion. The bulrush infusion in combination with the Cummings trap design seemed to provide resting site cues and collected males as well as empty and bloodfed females. Mosquito surveillance programs in California should include the systematic operation of dry ice-baited and gravid female traps to improve surveillance sensitivity for selected species in appropriate habitats.     

Identification of oviposition attractants for Culex quinquefasciatus from fermented Bermuda grass infusions.

Compounds which attract and stimulate oviposition by gravid Culex quinquefasciatus were isolated and identified from a fermented Bermuda grass infusion. The neutral portion of the ether extract of the aqueous infusion contained the stimulatory materials. Fractionation by liquid chromatography yielded an active fraction containing phenol, 4-methylphenol, 4-ethylphenol, indole and 3-methylindole. A blend of the 5 compounds strongly stimulated oviposition, as did blends of any 4 of them. Bioassays with individual compounds showed that only 3-methylindole consistently induced oviposition, in concentrations spanning 5 orders of magnitude.     

Influence of vegetation on carbon dioxide trap effectiveness for sampling mosquitoes in the Sierra Nevada foothills of Kern County, California.

The effect of vegetation on sampling Culex tarsalis, Cx. quinquefasciatus and Aedes nigromaculis by CO2 traps was evaluated at an intermittent stream habitat at the base of the Sierra Nevada foothills. Carbon dioxide traps were spaced along a 450 m transect perpendicular to Poso Creek to determine female attraction to traps placed in 5 different vegetation substrates: 1) open hilltop with sparse growth of grasses and saltbush, 2) open pasture with sparse growth of saltbush, 3) peripheral understory of mule fat, 4) shaded understory of mule fat, and 5) open canopy 5 m above ground in willow and cottonwood trees. Most host-seeking Cx. tarsalis and Cx. quinquefasciatus females were collected within the open canopy and peripheral understory. Host-seeking Ae. nigromaculis females were collected predominately in the open pasture and within the peripheral understory. The association between CO2 trap catch size and vegetation suggested a relationship between the host-feeding patterns and associated hunting strategies of these bird and mammal feeding species.     

Culex population dynamics and West Nile virus transmission in east-central Illinois

Temporal changes in the abundance Culex restuans and Culex pipiens were monitored in east-central Illinois for over a decade using infusion-baited oviposition traps. The 2 species typically exhibited a seasonal shift in relative abundance with a mean crossover date (when the proportion of egg rafts from both species is equal) of August 10 or 11, depending on leap year, with a 95% confidence interval of +/- 10.7 days. The date of crossover was linearly related to the date of last spring frost and occurred on average about 123 days after the last spring frost. Despite the predictability of crossover, the weekly pattern in the proportion of Cx. pipiens before and after crossover varied considerably, even between years with similar crossover dates. After West Nile virus became established in our area, we found that transmission based on Culex from gravid traps did not increase until Cx. pipiens abundance increased in oviposition traps. Infection rates peaked within the half-month period after crossover. The peak in Cx. pipiens abundance in oviposition traps during this 3-year period was between the 2nd half of August and the end of September. A higher magnitude of transmission in 2002 coincided with warmer temperatures during July and August and an extended period in which the 2 Culex species were in relatively equal abundance.