Evaluating sampling method bias in Culex tarsalis and Culex quinquefasciatus (Diptera: Culicidae) bloodmeal identification studies

Determining the bloodmeal hosts of the Culex vectors of encephalitis viruses such as West Nile virus is essential for understanding the role of these mosquitoes in enzootic and epidemic transmission. Although molecular techniques have increased our knowledge of blood feeding patterns by allowing host identification to the species level, few studies have focused on the role that sampling methods may play in determining these patterns. In the current study, we identified 644 bloodmeals from Culex tarsalis Coquillett and Culex quinquefasciatus Say females collected in CO2 traps (dry ice-baited Center for Disease Control traps), in gravid traps, and aspirated from resting sites. There was no significant difference in the bloodmeal host apportionment in sampling methods such as gravid traps and resting collections that collected fully engorged females. However, CO2 traps that collected partially fed females had a significantly different apportionment of hosts than either gravid or resting collections. Bloodfed females from CO2 traps had either fed on only a small subset of available host species or were biased toward more mammalian and fewer nonpasserine avian feeds than females from other collections. Because both full and partial bloodmeals can contribute to viral transmission, obtaining Culex bloodmeal collections from multiple sampling methods may be important to fully interpret the role of these mosquitoes as maintenance and/or bridge vectors.     

Factors influencing the outcome of mark-release-recapture studies with Culex tarsalis (Diptera: Culicidae)

Three potentially important aspects of mark-release-recapture experimentation were addressed: 1) source of mosquitoes for release, 2) time of release, and 3) weather during recapture. Culex tarsalis Coquillett mosquitoes collected as adult host-seeking females from dry ice-baited traps (CO2 traps) operated within the study area (local) were recaptured more frequently than females collected from traps operated outside the study area (foreign) or reared from field-collected immatures (reared). These results supported published studies on Anopheles and Ochlerotatus that indicated mosquitoes may "memorize" flight paths within their environment. Releasing gravid females provided a potentially useful replacement for reared females, because these gravids oviposited at wetlands and then dispersed to upland traps. Releasing local, foreign, or reared mosquitoes just after sunrise or just before sunset did not alter recapture success or the distance dispersed. Elevated wind speeds inhibited dispersal from protected microhabitats with citrus orchards and resulted in most recaptures being found at the leeward portion of the orchard.     

Evaluation of four sampling techniques for surveillance of Culex quinquefasciatus (Diptera: Culicidae) and other mosquitoes in African rice agroecosystems

Field studies were conducted in a rice, Oryza sativa L., agroecosystem in Mwea Kenya to compare the efficiency of CO2-baited Centers for Disease Control (CDC) light traps against nonbaited CDC light traps and gravid traps against oviposition traps in outdoor collection of Culex quinquefasciatus Say (Diptera: Culicidae) and other mosquitoes. Collectively, 21 mosquito species from the genera Culex, Anopheles, Mansonia, Ficalbia, and Aedes were captured during the 10-wk study period. Cx. quinquefasciatus was the predominant species in all trap types with proportions ranging from 57% in the nonbaited CDC light traps to 95% in the gravid traps. Significantly higher numbers of Cx. quinquefasciatus and Culex annulioris Theobald were collected in the CO2-baited CDC light traps than in the nonbaited CDC light traps, but the numbers of other mosquito species, including malaria vectors Anopheles arabiensis Patton and Anopheles funestus Giles did not differ significantly between the two trap types. More Cx. quinquefasciatus females were collected in grass infusion-baited gravid traps than egg rafts of this species in oviposition traps containing the same infusion. Although most mosquitoes captured in CO,-baited and nonbaited CDC light traps were unfed, most of those collected in gravid traps were gravid. From these findings, it is concluded that at least in the rice-growing area of Mwea Kenya, CO2-baited CDC light traps in conjunction with gravid traps can be used in monitoring of Cx. quinquefasciatus both for control and disease surveillance.     

Seasonal distribution, biology, and human attraction patterns of culicine mosquitoes (Diptera: Culicidae) in a forest near Puerto Almendras, Iquitos, Peru

This study was conducted as part of a field ecology study of arboviral activity in the Amazon Basin, Peru, to determine the taxonomy, frequency, seasonal, and vertical distributions of potential mosquito vectors. In addition, the relative efficiency of human-landing collections and dry ice-baited Centers for Disease Control (CDC)-type light traps was determined for collecting mosquitoes. A total of 70 species of mosquitoes from 14 genera were collected from June 1996 through December 1997 at a forested site near Puerto Almendras, approximately 20 km west-southwest of Iquitos, Peru. Three species [Psorophora (Janthinosoma) albigenu (Peryassu), Ochlerotatus (Ochlerotatus) fulvus (Wiedemann), and Ochlerotatus (Ochlerotatus) serratus (Theobald)] accounted for 70% of all mosquitoes captured in human-landing collections. Overall, biting activity occurred throughout the 24-h cycle but was higher during the daytime, primarily because of large populations of two day-biting species, Ps. albigenu and Oc. serratus. Oc. fulvus was active throughout the 24-h cycle but was more frequently collected during the evening. Oc. fulvus, Ps. albigenu, Culex (Melanoconion) pedroi Sirivanakarn & Belkin, and a mixture of Culex (Melaonoconion) vomerifer Komp, and Culex (Melanoconion) gnomatos Sallum, Huchings & Ferreira, accounted for 73% of the mosquitoes captured during darkness) by human collectors. In general, Ochlerotatus spp. and Psorophora spp. were more commonly captured in human-landing collections, whereas most Culex spp. were more frequently collected in the dry ice-baited CDC-type light traps. In general, mosquito populations were lowest from June through August when river levels were at their lowest. Two large population peaks occurred in November-December and in February-March as a result of "flood water" mosquito populations (e.g., Ps. albigenu). These data provide a better understanding of the taxonomy, population density, and seasonal distribution of potential mosquito vectors within the Amazon Basin region and allow for the development of appropriate vector and disease prevention strategies.     

Efficacy of four trap types for detecting and monitoring Culex spp. in north central Florida

The effectiveness of four types of mosquito traps at sampling Culex mosquitoes was compared at two north central Florida study sites (a commercial dairy and a swine research unit) with highly eutrophic lagoons that have a history of producing large populations of Culex mosquitoes. Traps evaluated included a John Hock (JH) model 1012 CDC style light trap, JH model 1712 CDC Gravid Trap (GT), and American Biophysics Corporation's Mosquito Magnet-Experimental (MM-X) and commercial model MM-Professional (MM-Pro) traps. The MM-X and MM-Pro traps are based on new counterflow technology. Culex nigripalpus Theobald and Culex quinquefasciatus Say were the two most abundant species collected, and they were the dominant species at the dairy site and swine research unit, respectively. Culex erraticus Dyar & Knabb and Culex salinarius Coquillett also were caught but in much lower numbers than the two dominant species at the swine unit, and rarely at the dairy site. At the dairy site the MM-Pro collection of total female Cx. quinquefasciatus was significantly greater than all other trap types (MM-Pro > GT > MM-X = CDC), and the MM-Pro also caught the most Cx. nigripalpus, but not significantly more than the CDC or MM-X (MM-Pro = CDC = MM-X > GT). At the swine research unit the largest number of female Cx. quinquefasciatus were caught in the MM-X trap, but the only significant difference was with the CDC trap (MM-X = MM-Pro = CT > CDC). For Cx. nigripalpus the CDC trap caught the most females, but these collections were only significantly different from the MM-Pro and GT (CDC = MM-X > MM-Pro > GT). The GT caught significantly more gravid female Cx. quinquefasciatus than all the other trap types at both sites, but collected very few gravid Cx. nigripalpus at either site.     

Prevalence and distribution of Ochlerotatus japonicus (Diptera: Culicidae) in two counties in southern New York State

The seasonal occurrence and abundance of a newly introduced mosquito in the United States, Ochlerotatus (Finlaya) japonicus (Theobald), are reported for Westchester and Putnam Counties in southern New York State. Adult mosquitoes were sampled at 39 sites distributed throughout the two counties. CDC (Centers forDisease Control and Prevention) light traps (2,107 trap nights) and gravid traps (1,813 trap nights) were used to collect a total of 44,428 mosquitoes from May through October 2000. Oc. japonicus was found at 97.4% of sites sampled and accounted for 9.8% of all specimens collected. Oc. japonicus was recovered from 1.5% (n = 326) of the light trap collections and 18.1% (n = 4,026) of the gravid trap collections. Although gravid traps collected significantly more specimens than light traps, the seasonal activity patterns measured by each trap type were congruent. In all, 30 mosquito species were collected. Unlike other Ochlerotatus or Aedes species, Oc. japonicus was collected throughout the study, indicating a broad seasonal activity period. There was significant regional variation in Oc. japonicus abundance, with higher trap densities occurring in the northern-most trapping sites. This study demonstrates that Oc. Japonicus is established in southern New York State.     

Sampling gravid Culex quinquefasciatus (Diptera: Culicidae) in Tanzania with traps baited with synthetic oviposition pheromone and grass infusions

The effectiveness of traps baited with (5R,6S)-6-acetoxy-5-hexadecanolide (the synthetic oviposition pheromone) and grass infusions in sampling a population of gravid Culex quinquefasciatus Say was conducted in Muheza, Northeast Tanzania. A counterflow geometry (CFG) trap baited with pheromone and set outdoors, adjacent to a pit latrine building, collected more gravid Cx. quinquefasciatus than a CDC trap baited with pheromone and operated without light. Inside pit latrine buildings, significantly more gravid Cx. quinquefasciatus were collected in a CFG trap-baited with pheromone or grass infusion than in traps baited with tap water. CFG traps baited with either grass infusion or pheromone and set outdoors, away from known breeding sites, caught significantly more gravid Cx. quinquefasciatus than traps baited with tap water. CFG traps baited with pheromone + grass infusion caught significantly more gravid Cx. quinquefasciatus than CFG traps baited with either grass infusion or pheromone. In both cases, the proportion of gravid mosquitoes increased as traps were moved away from a natural emergence site. More gravid Cx. quinquefasciatus were collected in a pheromone-baited CFG trap than were egg rafts deposited in a jar with pheromone-treated water. It is concluded that CFG traps baited with oviposition attractants can be used effectively to sample gravid Cx. quinquefasciatus.     

Electroantennogram and oviposition bioassay responses of Culex quinquefasciatus and Culex tarsalis (Diptera: Culicidae) to chemicals in odors from Bermuda grass infusions

Odors were collected from the headspace above fermented infusions of Bermuda grass, which commonly are used as attractants in traps for gravid mosquitoes. Coupled gas chromatography-electroantennogram detection (GC-EAD) was used to identify 9 compounds (phenol, p-cresol, 4-ethylphenol, indole, 3-methylindole, nonanal, 2-undecanone, 2-tridecanone, naphthalene) from odor extracts that elicited significant antennal responses from antennae of gravid female Culex quinquefasciatus Say and Culex tarsalis Coquillett mosquitoes. Several of these compounds at appropriate concentrations were weakly attractive to gravid female mosquitoes in laboratory bioassays and/or stimulated more oviposition than water controls. In addition, dimethyltrisulfide, a significant component of odor extract which did not elicit strong responses from female mosquito antennae in GC-EAD assays, also appeared to stimulate oviposition at 1 concentration. A reconstituted blend of the 10 compounds resulted in much stronger and more consistent responses than individual compounds. The blend was attractive to gravid Cx. quinquefasciatus and enhanced oviposition over a range of concentrations spanning 3 orders of magnitude. One concentration of the blend also attracted gravid Cx. tarsalis and enhanced oviposition. However, at the highest concentration tested, the blend was repellent to both species. Overall, these studies demonstrated that gravid mosquitoes are attracted to oviposition sites by blends of compounds rather than by individual chemicals, and that the concentration of compounds in the odor is a critical factor in determining whether responses are positive (attractive, stimulatory) or negative (repellent, deterrent).     

Rainfall-directed oviposition behavior of Culex nigripalpus (Diptera: Culicidae) and its influence on St. Louis encephalitis virus transmission in Indian River County, Florida

Resting Culex nigripalpus Theobald were collected with a ground aspirator three times a week in Indian River County, Fla., from January 1985 through December 1987. The number of green (newly emerged), empty, blood-fed, and gravid females in each collection was counted; up to 100 empty females were dissected to estimate the abundance of empty, parous females in the population. In general, this species was uncommon during the dry season from January through June but increased during the wet season in July and remained abundant through early winter. During the wet season, green, parous, and gravid females were periodically abundant. Time series analysis demonstrated that green and parous mosquitoes were positively associated through time and that gravid females were associated negatively with daily rainfall. The strongest correlations were recorded in 1985, a year during which St. Louis encephalitis virus was detected with increased frequency in Indian River County. Laboratory experiments in a large outdoor wind tunnel confirmed that high relative humidity was important for the initiation and successful completion of oviposition by gravid, field-collected Cx. nigripalpus mosquitoes. Thus, intermittent rainfall during autumn may serve to delay oviposition, increase longevity, synchronize blood feeding, and enhance transmission of St. Louis encephalitis virus by infected mosquitoes in the field.     

Entomological study on transmission of avian malaria parasites in a zoological garden in Japan: bloodmeal identification and detection of avian malaria parasite DNA from blood-fed mosquitoes

Several species of captive and wild birds have been found to be infected with various avian blood protozoa in Japan. We investigated the prevalence and transmission of avian malaria parasite and determined the bloodmeal hosts of mosquitoes collected in a zoological garden in Tokyo, Japan, by using the polymerase chain reaction. In total, 310 unfed and 140 blood-fed mosquitoes of seven species were collected by using sweep nets and CDC traps. Bloodmeal identification indicated that mosquitoes had fed on 17 avian and five mammalian species, including captive animals. The results of avian malaria parasite detection from mosquitoes with avian bloodmeals indicated that Culex pipiens pallens Coquillet is a main vector of avian Plasmodium in the current study site and that some captive and wild birds could be infected with avian malaria parasites. Furthermore, the distances between the collection site of blood-fed mosquitoes and the locations of their blood-source captive animals were estimated. Most females with fresh bloodmeals were found within 40 m of caged animals, whereas half-gravid and gravid females were found between 10 and 350 m from caged host animals. We demonstrated that blood-fed mosquitoes can provide useful information regarding the mosquito vector species of avian malaria parasites and allows for noninvasive detection of the presence of avian malaria parasites in bird populations.     

West Nile virus-infected dead corvids increase the risk of infection in Culex mosquitoes (Diptera: Culicidae) in domestic landscapes

A comparative study of West Nile virus (family Flaviviridae, genus Flavivirus, WNV) infection rates in Culex mosquitoes collected at 13 sites, seven reporting WNV-positive dead corvids (case sites) and six without reported dead birds (control sites) was conducted in Davis, CA, from 14 to 21 July at the beginning of the 2006 WNV outbreak. In total, 3051 Culex mosquitoes were collected using gravid traps and CO2-baited traps; WNV-infected mosquitoes were only collected with CO2-baited traps. WNV-infected Culex pipiens L. were collected at one of the seven case sites. Six of seven case sites yielded WNV-infected Culex tarsalis Coquillett, whereas only one of six control sites had WNV-infected Cx. tarsalis. Overall, the odds of finding WNV-positive mosquitoes were 19.75 times greater at sites reporting a WNV-infected dead corvid than sites without a WNV-infected dead corvid. Maximum likelihood estimates of the overall infection rates at the case sites were 3.48/1000 for Cx. tarsalis and 8.69/1000 for Cx. pipiens compared with 1.02/1000 in Cx. tarsalis collected at the control sites. Results indicate that Cx. tarsalis was important in early season enzootic transmission within Davis and that sites reporting WNV-infected dead corvids are areas to focus control and surveillance efforts.     

Quantitative evaluation of sampling methods for Ixodes dammini and Amblyomma americanum (Acari: Ixodidae).

Three tick-sampling methods (dry ice-baited tick traps, cloth drags, and ambulatory human host) were evaluated to determine which technique yielded the greatest capture of host-seeking stages of Ixodes dammini Spielman, Clifford, Piesman & Corwin and Amblyomma americanum (L.). The most reliable method, catching more stages and significantly more numbers of I. dammini and A. americanum; was dry ice-baited tick traps. There were no significant differences between the drag and human-host methods for any stage of ticks (I. dammini and A. americanum) collected. The numbers of ticks caught during the study were 5,052 by dry ice-baited tick traps, 199 by cloth drags, and 89 by ambulatory human host.     

Entomological evaluation of malaria vectors at different altitudes in Hai district, northeastern Tanzania

Entomological monitoring in four villages situated along an altitude transect in the Hai District of Northeastern Tanzania identified Anopheles arabiensis Patton as the principal vector of malaria and detected seasonal changes in vector behavior. Over a 13-mo sampling period, 10,557 mosquitoes were collected with CDC light traps, pyrethrum spray catches, and pit traps of which 5,969 (56.5%) wereAn. arabiensis, 762 (7.2%) wereAnopheles funestus Giles s.l., 3,578 (33.9%) were culicines, and 248 (2.3%) were nonvector anophelines. Vector densities declined rapidly with increasing altitude, demonstrating a 50% decrease in annual human biting rate for every 86-m rise in altitude. Light traps were found to be more efficient than spray catches for the collection of An. arabiensis. This observation was attributed to increased exophily of this species, most notably in the wet season, and is supported by seasonal changes in the human blood index and fed/gravid ratio. These results indicate that spray catches may underestimate the abundance of exophilic vectors such as An. arabiensis and that entomological monitoring may require more than one collection method, especially at low vector densities. The annual entomological inoculation rate (EIR) decreased sharply with increasing altitude, with large variation around the estimate at low vector densities. Increased transmission because of unpredictable short rains at low altitudes and spatial clustering of infective mosquitoes may contribute to elevated EIR estimates.     

Arbovirus transmission by Culex nigripalpus in Florida, 2005

Understanding the transmission patterns of West Nile and St. Louis encephalitis viruses (family Flaviviridae, genus Flavivirus, WNV and SLEV) could result in an increased ability to predict transmission risk to humans. To examine transmission patterns between vector and host, we trapped mosquitoes in three Florida counties from June to November 2005 by using chicken-baited lard can mosquito traps. These traps were used to monitor for presence of WNV and SLEV in mosquitoes and subsequent transmission of these viruses to chickens. In total, 166,615 female mosquitoes were sorted into 4,009 pools based on species and bloodfed status, and they were tested for presence of WNV and SLEV. Sera from 209 chickens were tested for WNV and SLEV antibodies. We detected eight WNV-positive Culex nigripalpus Theobald mosquito pools; SLEV was not detected in any pools. Six positive pools were collected in August and September from Duval County, one pool in September from Manatee County, and one pool in November from Indian River County. Of the eight chickens potentially exposed to WNV, antibodies were detected in only one chicken, indicating a low rate of transmission relative to the observed mosquito infection rates. Low virus transmission rates relative to infection rates would suggest that using sentinel chicken seroconversion data as a means of arbovirus surveillance may underestimate the prevalence of WNV in the mosquito population. However, using mosquito infection rates may overestimate the risk of arboviral transmission. A variety of factors might account for the observed low level of transmission including a lack of viral dissemination in mosquito vectors.     

Oviposition activity patterns and West Nile virus infection rates for members of the Culex pipiens complex at different habitat types within the hybrid zone, Shelby County, TN, 2002 (Diptera: Culicidae)

Oviposition activity and West Nile virus (family Flaviviridae, genus Flavivirus, WNV) infection rates were assessed for members of the Culex pipiens complex from July through December 2002 by using gravid traps placed at four ecologically different sites in the southern portion of the hybrid zone in Shelby County, TN. Molecular assays identified three members of the Cx. pipiens complex: Cx. pipiens pipiens L., Cx. p. quinquefasciatus Say, and Cx. p. pipiens-Cx. p. quinquefasciatus hybrids (hybrids). The Cx. pipiens complex accounted for 90% of mosquitoes collected in gravid traps. All 285 WNV-positive mosquitoes were Culex mosquitoes, and 277 (97%) were Cx. pipiens complex mosquitoes. Infection rates among members of the Cx. pipiens complex were not significantly different. Infection rates were significantly higher at two urban sites than at a rural site, and WNV was not detected at a forested site. At urban sites, abundances of members of the Cx. pipiens complex corresponded to a simple latitude model of the hybrid zone. Cx. p. quinquefasciatus was most abundant (46.4%), followed by hybrids (34.1%) and Cx. p. pipiens (19.5%). The relative abundances at a rural site were reversed with Cx. p. pipiens (48.4%) being most abundant. This demonstrates that spatial habitat variation may profoundly influence the distribution of members of the Cx. pipiens complex within the hybrid zone. Members of the Cx. pipiens complex did not display different oviposition patterns. However, oviposition patterns assessed hourly at urban and rural sites were significantly different. At urban sites, oviposition activity of Cx. pipiens complex mosquitoes was bimodal with an evening peak associated with sunset and a morning peak associated with sunrise. At the rural site, the evening peak was pronounced and the morning peak weak and similar to nighttime activity.     

Arthropod faunal composition on Kentucky equine premises

Thirty-nine arthropod species representing the families Muscidae, Chloropidae, Tabanidae, Simuliidae, Culicidae, and Ixodidae were collected from Kentucky equine premises using dry ice-baited canopy traps, light traps, water samples, tick drags, and animal inspections during late April to mid-October 1987 and 1988. Thirty-three species were collected from canopy traps, consisting of 74.3% muscid, 16.7% chloropid, 5.0% simuliid, 3.8% tabanid, and 0.2% culicid species. Light traps attracted eight culicid and water samples yielded three culicid species. One ixodid species was collected with drags, and animal inspections yielded two muscid and two ixodid species. Comparison of species assemblages among farms and across years using multivariate principal component analysis (PCA) yielded three distinct principal components, and PCA scores for each farm per year were correlated with biotic and abiotic environmental factors and management practices. The proximity to cattle herds was the best predictor of similarity in species assemblages among farms, reflecting the high percentage of muscid species collected. Poor management practices were partially responsible for proportionally larger populations of culicids, ixodids, and muscids on some farms.     

Isolation of viruses from mosquitoes (Diptera: Culicidae) collected in the Amazon Basin region of Peru

As part of a comprehensive study on the ecology of arthropod-borne viruses in the Amazon Basin region of Peru, we assayed 539,694 mosquitoes captured in Loreto Department, Peru, for arboviruses. Mosquitoes were captured either by dry ice-baited miniature light traps or with aspirators while mosquitoes were landing on human collectors, identified to species, and later tested on Vero cells for virus. In total, 164 virus isolations were made and included members of the Alphavirus (eastern equine encephalomyelitis, Trocara, Una, Venezuelan equine encephalomyelitis, and western equine encephalomyelitis viruses), Flavivirus (Ilheus and St. Louis encephalitis), and Orthobunyavirus (Caraparu, Itaqui, Mirim, Murutucu, and Wyeomyia viruses) genera. In addition, several viruses distinct from the above-mentioned genera were identified to the serogroup level. Eastern equine encephalomyelitis virus was associated primarily with Culex pedroi Sirivanakarn & Belkin, whereas Venezuelan equine encephalomyelitis virus was associated primarily with Culex gnomatos Sallum, Huchings & Ferreira. Most isolations of Ilheus virus were made from Psorophora ferox (Von Humboldt). Although species of the Culex subgenus Melanoconion accounted for only 45% of the mosquitoes collected, 85% of the virus isolations were made from this subgenus. Knowledge of the viruses that are being transmitted in the Amazon Basin region of Peru will enable the development of more effective diagnostic assays, more efficient and rapid diagnoses of clinical illnesses caused by these pathogens, risk analysis for military/civilian operations, and development of potential disease control measures.     

Field sampling rate of BG-sentinel traps for Aedes aegypti (Diptera: Culicidae) in suburban Cairns, Australia

Mini-mark-release-recapture experiments were conducted in suburban Cairns, Australia to establish the sampling rate of the Biogents-Sentinel (BGS) trap for adult Aedes aegypti (L.). Small cohorts of marked mosquitoes (30 females and 15 males) were released at typical Cairns residences, and the number of marked mosquitoes recaptured in the BGS trap after 24 h was recorded. The sampling rate was compared between two seasons and two common housing styles (high-set 'Queenslander-style' timber and low-set brick houses), between old gravid and young nulliparous females, and between mosquitoes released in different areas of a house. Overall, the BGS traps recaptured a mean (+/- SEM) of 24.6% (+/- 1.9) of the released marked female mosquitoes in 24 h. The mean recapture rate for females was significantly higher in the dry season (30.4% +/- 2.8) compared with the wet (18.8% +/- 2.2). The overall recapture rates did not differ significantly between the two house types, but variability between the individual premises was high. An overall mean of 18.2% (+/- 1.7) of males was collected. Recapture rates of young nullipars and older gravid females were similar. These recapture rates can be used to estimate the population density of Ae. aegypti females in north Queensland, although it will provide an underestimate as trap sample was largely representative of mosquitoes present in the same area as the trap, and not from other areas of the house.