Adult mosquito trap sensitivity for detecting exotic mosquito incursions and eradication: a study using EVS traps and the Australian southern saltmarsh mosquito, Aedes camptorhynchus

Adult mosquito traps are commonly used in biosecurity surveillance for the detection of exotic mosquito incursions or for the demonstration of elimination. However, traps are typically deployed without knowledge of how many are required for detecting differing numbers of the target species. The aim of this study was to determine the sensitivity (i.e., detection probability) provided by carbon dioxide-baited EVS traps for adult female Australian southern saltmarsh mosquitoes, Aedes camptorhynchus, a recent biosecurity problem for New Zealand. A mark-release-recapture study of three concurrently released cohorts (sized 56, 296, and 960), recaptured over four days with a matrix of 20 traps, was conducted in Australia. The detection probability for different numbers of traps and cohorts of different sizes was determined by random sampling of recapture data. Detection probability ranged from approximately 0.3 for a single trap detecting a cohort of 56 mosquitoes to 1.0 (certainty of detection) when seven or more traps were used. For detection of adult Ae. camptorhynchus around a known source, a matrix of traps provides a strong probability of detection. Conversely, the use of single traps deployed over very large areas to detect mosquitoes of unknown entry pathway is unlikely to be successful. These findings have implications for the design of mosquito surveillance for biosecurity.     

Efficacy of bird-baited traps placed at different heights for collecting ornithophilic mosquitoes in eastern Queensland, Australia

To compare the efficacy of bird-baited traps with standard CO₂-baited Centers for Disease Control (CDC) light traps for collecting ornithophilic mosquito species, seven Latin square trials were conducted at six urban sites in Cairns and Brisbane, Australia. Traps were placed 1 m above ground level and 5–10 m according to tree canopy height. CO₂-baited CDC traps consistently collected more mosquitoes of all species than the bird-baited traps at all locations. In Brisbane, CO₂-baited CDC traps placed at ground level collected significantly more Culex annulirostris Skuse than those at canopy height during two trials, and more Aedes vigilax (Skuse) and Ae. procax (Skuse) during one trial each. Conversely, in Cairns, CO₂-baited CDC traps placed in the tree canopy collected significantly more Cx. squamosus (Taylor) during two trials, and significantly more Aedeomyia catasticta Knab and Cx. cubiculi Marks during one trial each. Consistently low yields of ornithophilic species including Cx. australicus Dobrotworsky & Drummond and Cx. quinquefasciatus Say in all traps tested suggests the need to employ alternative trapping measures to target these species in urban areas.     

Vector competence of Coquillettidia linealis (Skuse) (Diptera: Culicidae) for Ross River and Barmah Forest viruses

Abstract Coquillettidia linealis is a severe pest on some of the Moreton Bay islands in Queensland, Australia, but little is known of its breeding habitats and biology. Because of its high abundance and its association with Ross River (RR) and Barmah Forest (BF) viruses by field isolation, its vector competence was evaluated in the laboratory by feeding dilutions of both viruses in blood. For RR, Cq. linealis was of comparable efficiency to Ochlerotatus vigilax (Skuse), recognised as being a major vector. Results were as follows for Cq. linealis and Oc. vigilax , respectively: dose to infect 50%, 10^2.2 and <10^1.7 CCID₅₀/mosquito; 88% and 90% disseminated infection at 4 days postinfection; transmission at 4 days with rates of 68−92% and 25−60%. For BF dose to infect 50%, 10^2.7 and 10^2.0; disseminated infection rates on first transmission day (day 6), 40% and 70%; transmission rates of 8−16% and 0−10%. As a capillary-tube method was used rather than suckling mice to demonstrate transmission, transmission rates may be underestimates. This, the first study of the vector competence of Cq. linealis in Australia, demonstrates that this species deserves control on the southern Moreton Bay islands.     

Mosquito‐borne West Nile virus (WNV) surveillance in the Upper Rhine Valley,Germany

West Nile virus (WNV) could be introduced into Germany via migratory birds originating from Africa or southern Europe and subsequently transmitted to indigenous birds, humans, or horses by mosquitoes. Neither the virus itself nor antibodies against WNV have yet to be found in mosquitoes and horses, whereas antibodies have been detected in migrating birds and in humans that were in close contact with birds. At present, the West Nile virus itself has yet to be detected in Germany. This investigation was conducted primarily in major bird breeding, resting, and roosting habitats (hotspots) in the Upper Rhine Valley. Adult mosquitoes were trapped using CO₂‐baited Encephalitis Vector Surveillance (EVS)‐traps and were tested for WNV by the VecTest WNV Antigen Assay. In 2007 and 2008, a total of 11,073 host‐seeking adult female mosquitoes (13 species) were tested, and all tests were negative for WNV. Statistical calculations could be performed only where sufficient numbers of mosquitoes were trapped. For these sites, WNV infection among mosquitoes could be ruled out with 80% certainty. For the evaluation of the WNV situation in Germany, the results of this investigation are a further indication that the virus has not yet arrived.     

Collection of wind-borne haematophagous insects in the Torres Strait,Australia

Circumstantial evidence has implicated wind-borne mosquitoes (Diptera: Culicidae) in the introduction of Japanese encephalitis (JE) virus into Australia from the New Guinea mainland. A study was initiated on Saibai Island in the northern Torres Strait, during January and February 2000, to identify the potential source of insects collected in aerial (kytoon) and surface-level traps. Wind speed and direction were recorded to determine wind profiles during insect sampling. Northerly winds capable of carrying insects from New Guinea to Saibai Island were only present on three out of 18 nights sampled. Only three male mosquitoes, comprising two Verrallina funerea (Theobald) and one Ochlerotatus vigilax (Skuse), were collected in aerial samples, and were most likely of local origin. Culicoides midges were also collected in aerial nets and included gravid/parous C. bundyensis Lee and Reye, and one parous C. histrio Johannsen. Highest densities of arthropods (up to 1562/million m3) were on 30 January 2000 when NW winds, sustained for six hours, probably introduced midges from the New Guinea mainland. Adult mosquitoes (including three female Ve. funerea and a single female Ficalbia) and Culicoides (including two gravid C. bundyensis and one parous C. cordiger Macfie) were also collected in 2 m high mast nets during northerly surface winds. Although the results do not provide evidence that wind-blown mosquitoes introduced JE from New Guinea into Australia, they do not preclude that strong N winds associated with low pressure systems SW of the Torres Strait could have done so. However, results suggest that Culicoides were more likely than mosquitoes to reach high altitude and travel long distances during the light N winds experienced during the study.     

SEASONAL ABUNDANCE OF MOSQUITOES IN A NATIVE FOREST OF THE MURRAY VALLEY OF VICTORIA, 1979–1985

Abstract
From 1979 to 1985, mosquitoes were collected from Kanyapella state forest near Echuca in the Murray Valley floodplain of Victoria using dry-ice baited light traps. 12 species were recorded during the study, and their relative prevalence is presented as seasonal values. Culex annulirostris Skuse was the predominant summer species, and Aedes sagax (Skuse) was generally the most common species during autumn and winter, but each of the following species, Aedes bancroftianus Edwards, Ae sagax, Ae theobaldi (Taylor), Anopheles annulipes Walker s. l., and Cx annulirostris , was the most common during at least one of the spring periods.     

Timing of host-seeking behaviour of the mosquitoes Anopheles annulipes sensu lato Walker and Coquillettidia linealis (Skuse) (Diptera: Culicidae) in the Murray River Valley, South Australia

Abstract  The timing of host-seeking behaviour was studied in two mosquito species, Anopheles annulipes sensu lato and Coquillettidia linealis at Mundic Creek, near the Upper River Murray in South Australia. Hourly sampling using carbon dioxide-baited traps revealed consistent patterns in the timing of host-seeking. Coquillettidia linealis displayed a very large peak in host-seeking activity at sunset, followed by a much reduced level throughout the night and a smaller peak at sunrise. Anopheles annulipes s.l. differed by displaying a significantly smaller peak at sunset, followed by higher amount of activity throughout the night compared with Cq. linealis . The two taxa, while both crepuscular and nocturnal, spread their host-seeking effort out differently throughout the night, indicating that they have different resource requirements.     

Evidence of vertical transmission of West Nile virus in field‐collected mosquitoes

Male and nulliparous female mosquitoes were surveyed for evidence of vertical WNV infection in East Baton Rouge Parish, Louisiana. Adult male mosquitoes collected by trapping and aspiration, and adult male and nulliparous female mosquitoes reared from field‐collected larvae were tested. Adult male Culex spp., female Aedes albopictus (Skuse), and female Culex quinquifasciatus Say mosquitoes that were collected as larvae were test‐positive for WNV RNA. Infectious WNV was detected using virus isolation in field‐collected male Aedes triseriatus Say and Culex salinarius Coquillett; these data represent the first field evidence of vertical transmission of WNV in Ae. triseriatus and Cx. salinarius.     

Blood meal sources of mosquitoes captured in municipal parks in São Paulo,Brazil

The aim of this study was to investigate blood meal sources of mosquitoes captured in municipal parks in the city of São Paulo, Brazil, and to identify possible associations between mosquito species and their food preferences. Fourteen species of blood hosts of 510 engorged adult female mosquitoes were identified using PCR assays with a vertebrate‐specific primer set based on cytochrome b mitochondrial DNA of the following vertebrates: birds, dogs, cats, rodents, humans, and other primates. Mosquitoes were captured using a manual aspirator, CDC traps in the canopy, CDC traps at ground level, and Shannon traps. With the exception of cats, all other vertebrates were used as hosts by mosquitoes in the parks. Statistical analysis failed to show any trend toward association between most culicid species captured and the sources of blood meals. Instead, they revealed random patterns, indicating that the mosquitoes fed on the most abundant or convenient blood meal sources. Although feeding preferences were observed in two species (birds in the case of Cx. nigripalpus and dogs in the case of Cx. quinquefasciatus), our results highlight the opportunistic feeding habits of the female mosquitoes in this study.     

Mosquito (Diptera: Culicidae) fauna in an area endemic for West Nile virus

Mosquito collections with CDC light traps using dry ice and pigeon‐baited traps were carried out in south Moravia (Czech Republic) from April to October in 2007 and 2008 at two study sites. In 2007, 11 two‐day captures were carried out in two‐week intervals, and 1,490 female mosquitoes of nine species were caught. In 2008, 15 two‐day trappings of mosquitoes were carried out: 6,778 females of 22 species of mosquitoes were trapped. The results showed marked differences in abundance and species composition of mosquitoes between both study sites and between the trapping methods. In the floodplain forest ecosystem of the Soutok study area, Aedes vexans predominated. The species composition in the Nesyt study site was more varied and the most common species was Culex pipiens. At the latter study site, Anopheles hyrcanus (var. pseudopictus) and Uranotaenia unguiculata, mosquito species with largely southern Eurasian distribution, were repeatedly demonstrated. The largest capture of mosquitoes was in traps with CO₂ placed at a height 1 m above the ground. The capture of mosquitoes in the pigeon‐baited traps as well as in the traps with CO₂ placed in the canopy of trees was markedly lower in both study sites, with the predominant species being Culex pipiens.     

Horizontal and vertical dispersal of dengue vector mosquitoes, Aedes aegypti and Aedes albopictus, in Singapore

To study the dispersal of dengue vector mosquitoes in Singapore, females of Aedes aegypti (L.) and Aedes albopictus (Skuse) (Diptera: Culicidae) were fed blood containing rubidium (Rb), which was detectable in their eggs by means of Graphite Furnace Atomic Absorption Spectrophotometry (GFAAS). Laboratory calibration of the Rb reading, for a range of egg numbers from Rb-fed females, indicated a reasonably linear relationship and an unequivocal distinction between results with zero and one marked egg. Rb-marked female Aedes mosquitoes aged 3-5 days were released in semi-rural and urbanized parts of Singapore, with an array of ovitraps extending to a radius of 320 m from the release point. Subsequently, Rb-marked Aedes eggs were detected throughout the array, with similar distributions on each of the 4 days after release. More Rb was detected nearer the release point. However, when correction was made for the greater areas of zones further from the release point (and therefore presumably existence of more alternative oviposition sites), there were no significant differences in the numbers of marked eggs per ovitrap in the zones nearer or further from the release points. It is concluded that females of both these Aedes (Stegomyia) species could disperse easily and quickly throughout areas of radius 320 m in search of oviposition sites. This contrasts with the general belief that Ae. aegypti seldom flies more than 50 m and that control operations can safely be based on such an assumption. Releases on level 12 of a 21-storey apartment block, with ovitraps on each storey, showed similar easy and rapid dispersal to the top and bottom of the block.     

Biological control of container-breeding mosquitoes, Aedes albopictus and Culex quinquefasciatus, in a Japanese island by release of Toxorhynchites splendens adults

To control container-breeding mosquitoes in the small island of Minnajima (0.56 km2), northern Okinawa, Japan, laboratory-reared adults (aged 7-10 days) of Toxorhynchites splendens (Palawan strain), a mosquito with predatory larvae, were released repeatedly during 1984, 1986 and 1987. Thirteen species of mosquitoes (Diptera: Culicidae) occurred in artificial containers, ground pools or crab-holes on the island, the predominant species being Aedes (Stegomyia) albopictus and Culex (Culex) quinquefasciatus. Predatory mosquito larvae of Culex (Lutzia) fuscanus and Cx (Lt.) halifaxii were found commonly in wet containers. In the first year of study, during a period of 54 days from 13 May to 5 July 1984, totals of 879 female and 806 male adults of Tx.splendens were released on six occasions. Similarly, between 29 April and 30 August 1986, totals of 2920 female and 2878 male adult Tx.splendens were released. In the third study year, totals of 2041 female and 1783 male Tx.splendens were released on eight occasions during 199 days from 23 April to 7 November 1987. After adult releases at two sites, the immature stages of Tx.splendens were found in 164 out of 502 traps in 1984, 421 out of 933 traps in 1986, and 151 out of 502 traps in 1987. The number of immatures of Tx.splendens present in each trap varied from 1 to 40 in 1984, 1 to 29 in 1986 and 1 to 9 in 1987. Numbers of immatures of the target species found in the traps during August-September averaged 71.9/trap/month in 1984, 114.7/trap/month in 1986 and 36.0/trap/month in 1987, significantly less in the traps with Tx.splendens than in those without them. The present field studies indicated that, in this small island, approximately 250 adult female and 200 male Tx.splendens per month should be released from April to November, and the releases should be carried out every year, in order to control effectively the target mosquitoes Ae.albopictus and Cx quinquefasciatus breeding in artificial containers in Minnajima.     

Population structure and dispersal of the saltmarsh mosquito Aedes vigilax in Queensland, Australia

Population genetics of the mosquito Aedes vigilax (Skuse) (Diptera: Culicidae), a major vector of arboviruses (e.g. Barmah Forest, Ross River), were investigated to obtain an indirect estimate of mosquito dispersal characteristics in typical habitats of Aedes vigilax in south-east Queensland: on the off-shore islands of Moreton Bay and on the mainland where disjunct breeding populations of Ae. vigilax are distributed along intertidal marsh. Six allozyme loci were assessed for genetic differentiation between samples from 11 localities. Significant larval variation between some breeding sites was attributed to site-specific selection. Nonsignificant genetic differentiation was found among collections of adult mosquitoes caught in light traps throughout the study area (exceeding 60x27 km), indicating widespread dispersal. As distances of < or = 9 km over water did not appear to act as effective barriers to Ae. vigilax dispersal, localized control activities applied to Ae. vigilax breeding sites are unlikely to be effective against the vagile adult population. Therefore, the contiguous shires programme of broad acre control is endorsed to prevent the spread of arboviruses carried by Ae. vigilax     

Seasonal prevalence of mosquitoes collected from light traps in the Republic of Korea, 2005

Adult mosquito surveillance was conducted during 2005 at 22 US military installations and two training sites located in six provinces in the Republic of Korea. Adult mosquitoes were collected in New Jersey light traps from 1 May to 15 October to determine threshold levels to initiate pesticide applications based on trap indices. A total of 27 363 adult mosquitoes (22 368 [81.7%] females and 4995 [18.3%] males) comprising 15 species (including five members of the Anopheles sinensis group) belonging to seven genera were collected. The most common species collected were members of the Anopheles sinensis Wiedemann group (50.2%), followed by Culex tritaeniorhynchus Giles (30.6%), Aedes vexans nipponii (Theobald) (11.8%), and Culex pipiens Coquillett (6.3%) females. Trap indices varied widely for species over their range, due in part to geographical distribution and degree of association with urban or rural communities.     

Seasonal prevalence of mosquitoes collected from light traps in the Republic of Korea, 2006

Adult mosquito surveillance was conducted during 2006 at 22 US Army and Air Force installations and two training sites located in six provinces in the Republic of Korea. Adult mosquitoes were collected in New Jersey light traps from 1 May through 15 October 2006 to determine threshold levels to initiate pesticide applications based on trap indices. In total 16 217 adult mosquitoes [13 612 (83.9%) females and 2605 (16.1%) males] comprising 16 species (including five members of the Anopheles sinensis Group) belonging to eight genera were collected. Females of the most commonly collected species were members of the Anopheles sinensis Wiedemann Group (58.9%), followed by Aedes vexans nipponii (Theobald) (21.3%), Culex tritaeniorhynchus Giles (11.8%) and Culex pipiens Coquillett (5.2%). Trap indices varied widely for species over their range, due in part, to their geographical distribution and degree of association with urban or rural communities.     

Seasonal prevalence of mosquitoes collected from light traps in the Republic of Korea in 2003

Surveillance of adult mosquitoes was conducted at 29 US military installations and training sites in six provinces in the Republic of Korea during 2003. Adult mosquitoes were collected in New Jersey light traps and dry ice‐baited New Jersey light traps from 1 May to 15 October. Mosquito surveillance was conducted to determine threshold levels to initiate pesticide applications and identify malaria infection rates at selected army installations and training sites. A total of 42 024 adult mosquitoes (32 594 females [77.6%] and 9430 males [22. 4%]) comprising 14 species and Anopheles sinensis s.l. (a complex of five species), representing seven genera, were collected. The most common species were members of the Anopheles sinensis Wiedemann complex (54.9%), followed by Aedes vexans nipponii (Theobald) (19.0%), Culex pipiens Coquillett (14.3%) and Culex tritaeniorhynchus Giles (10.6%). Trap indices varied widely for species over their range, due in part to geographical distribution and degree of association with urban communities.     

Monitoring adult Eretmocerus mundus, Encarsia lutea and Bemisia tabaci with yellow sticky traps in cotton Gossypium hirsutum

Abstract:  The efficiency of yellow sticky traps for estimating adult population dynamics of Bemisia tabaci (Genn.) (Hom., Aleyrodidae) and its parasitoids Eretmocerus mundus Mercet, Encarsia lutea (Masi) (Hym., Aphelinidae) was examined in cotton in choice and no-choice studies in Çukurova, Turkey in 2004 and 2005. In the no-choice study, traps were suspended individually on the third, fifth or eighth main stem node branches from the tops of cotton plants. For the choice study, three traps were suspended on the same individual node branches on different plants. Trap captures were counted weekly. Mean (±SE) numbers of B. tabaci captured on traps were higher in no-choice (max.: 697.8 ± 55.6) compared with choice (max.: 533.3 ± 47.4) studies each year. Population fluctuation patterns of E. mundus and E. lutea adults were similar to those of adult B. tabaci on traps with low weekly mean numbers occurring initially and increasing to peak levels in mid-August, then decreasing in later weeks of the studies. The relationship between weekly mean numbers of B. tabaci and E. lutea was greater than the relationship between B. tabaci and E. mundus . Mean numbers of E. mundus and E. lutea on traps were higher at the third main stem nodes than traps suspended on the fifth or eighth node. Mean numbers of E. lutea pupae were usually higher than E. mundus from the first sampling date throughout the end of the growing season on leaves. The relationship between parasitoid pupae and adults captured in traps is discussed.