NSW Arbovirus Surveillance & Vector Monitoring Program

1999 - 2000 Annual Report

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MOSQUITO MONITORING

Methods.

Mosquitoes were collected overnight in dry-ice baited EVS type traps. They were then sent live in cool, humid eskies via overnight couriers to the Department of Medical Entomology at Westmead Hospital for identification and processing for arbovirus isolation. The mosquitoes were identified according to keys and illustrations in: 

·     'Mosquitoes and Mosquito-borne Disease in Southeastern Australia' (Russell, 1993), 'A Colour Photo Atlas of Mosquitoes of Southeastern Australia' (Russell, 1996), 'The Mosquitoes of Victoria' (Dobrotworsky, 1965), and the twelve volume series 'The Culicidae of the Australasian Region'  (Lee et al., 1980 - 1989; Debenham et al., 1989).

 Due to the many factors that influence mosquito abundance, it can be extremely difficult to describe and compare the population size of particular mosquito species between locations and seasons. Thus mosquito abundances are best described in relative terms, and in keeping with the terminology from previous reports, mosquito numbers are depicted as:

·     'low' (<50 per trap), 'moderate' (50-100 per trap), 'high' (101-1,000 per trap), 'very high' (>1,000 per trap), and ‘extreme’ (>10,000 per trap).

 All mosquito monitoring results (with comments on the collections) were placed on the NSW Arbovirus Surveillance Web site, and were generally available within 1-2 days of receiving the sample into the laboratory. Access to each location's result is from: http://www.arbovirus.health.nsw.gov.au/areas/arbovirus/results/results.htm.

A brief summary of the mosquito collections and virus isolations for each location follows. Complete mosquito details are available on the web site. A comprehensive list of the isolates is included below, in the section under 'Arbovirus Isolations'.

Results. Overall, 245,524 mosquitoes representing 67 species were collected in NSW during the 1999-2000 season. Culex annulirostris was the most abundant and most important of the inland mosquito species during the summer months, with Coquillettidia linealis the most abundant species collected on the coast. All of the isolates this year were from the inland with 18 Ross River (RR), 5 Sindbis (SIN) and 10 unknowns.

INLAND. 173,004 individual mosquitoes, comprising 33 species, were collected from inland NSW. Culex annulirostris was the dominant species trapped at most sites and generally comprised 60-90% of the collections. Anopheles annulipes was the next most common species.

Albury: mosquito numbers from both the Sewerage Treatment Works and the Water Treatment Plant were generally well below average for much of the season, with some ‘high’ collections of Culex annulirostris through February. No viruses were isolated.

Brewarrina: trapping occurred over a two-week period in March, and collections were dominated by Culex quinquefasciatus. Numbers during the first week were ‘high’. No viruses were isolated.

Bourke:  trapping was consistent this season from January to April, with traps set at the new sites of the Sewerage Treatment Works (STW) and Oxley Street. The STW was a particularly productive site, especially for Culex annulirostris, with ‘high’ mosquito numbers for much of January to March. Oxley Street trapped lower numbers, with Culex quinquefasciatus dominating the collections. Ross River was isolated on successive weeks from the STW in mid-January, with three isolates from Culex annulirostris. There were no flavivirus seroconversions in the sentinel chicken flocks.

Collarenebri: this new trapping location produced a series of ‘high’ mosquito collections through January to March, however they were dominated by Culex quinquefasciatus.  No viruses were isolated.

Condobolin: a new site of the Sewerage Treatment Works (STW) commenced this year at Condobolin. Except for January, with some ‘high’ collections, numbers tended to be below average. One ?Culex gelidus was trapped at the STW. No viruses were isolated and there were no flavivirus seroconversions in the sentinel chicken flocks.

Deniliquin: except for some ‘very high’ numbers during January, mosquito collections were below average for much of the season, and mostly ‘low’ from February onwards. One unknown isolate was collected mid-January from Culex annulirostris. There were no flavivirus seroconversions in the sentinel chicken flocks.

Forbes: collections were sporadic, with only four collections made this season, which were mostly ‘low’. No viruses were isolated and there were no flavivirus seroconversions in the sentinel chickens.

Fords Bridge: this is a new trapping site for the program. Following the heavy rains in February/March, this site produced some ‘very high’ numbers, with an ‘extreme’ collection made in late March. During this time, the floodwater mosquitoes, such as Aedes eidsvoldensis and Aedes theobaldi, dominated the collections. There were 10 isolates, including 2 RR, 2 SIN and 6 unknowns.

Griffith: three trapping sites continued for the 1999-2000 season. The large numbers collected through November/December of last season did not reoccur, although overall mosquito numbers were higher this season. This was due to the consistently ‘very high’ collections trapped up until April, especially at Willbriggie. Griffith mosquitoes yielded 15 arbovirus isolates (9 RR, 3 SIN and 3 unknown). There were no flavivirus seroconversions in the sentinel chicken flocks based at Hanwood and Barren Box Swamp.

Gunnedah: only one collection was made which trapped one Culex quinquefasciatus. No viruses were isolated.

Leeton:  the big collections from the 1998-1999 season were not repeated for 1999-2000, although ‘very high’ numbers, which were well above average, were trapped at Almond Road from late November through to early February. Two arboviruses were isolated, both RR collected on the 7.2.2000 from Culex annulirostris. None of the chickens seroconverted in the sentinel flocks.

Macquarie Marshes: this location undertook flavivirus surveillance in chicken sentinel flocks only, and no seroconversions were detected.

Menindee: no mosquito collections were made this season from Menindee. There were no flavivirus seroconversions in the sentinel chicken flocks.

Moree: trapping occurred at several sites within Moree and numbers were mostly ‘low' for the season. No viruses were isolated.

Tamworth: a new site of the ‘Caravan Park’ was added this season. Except for some ‘high’ collections from Oxley Vale in January to March, numbers were generally ‘low’ and below average throughout the season. No viruses were isolated.

Tibooburra: a small number of collections were made late in the season in response to reports of nuisance biting, with mostly ‘low’ numbers of Culex quinquefasciatus. No viruses were isolated.

Wanaaring: this new trapping site from the northwest of the state produced some ‘very high’ collections from January through to March, with floodwater Aedes (such as Aedes eidsvoldensis) and Culex quinquefasciatus dominating the collections. No viruses were isolated.

Wee Waa:  trapping occurred once only, with ‘low’ mosquito numbers. No viruses were isolated.

Wentworth: numbers were ‘low’ for much of the season. There were no virus isolates.

COASTAL. 63,614 mosquitoes comprising 50 species were collected from coastal NSW. Coquillettidia linealis was the most common species, comprising around 35% of the coastal mosquitoes. Aedes vigilax was the next most abundant and made up 27% of the collections.

Ballina: mosquito numbers were average for most of the season up until late March. Thereafter, a series of ‘high’ collections, which were well above average, were made especially from Greenfield Road. Like last season, freshwater mosquitoes dominated collections, particularly Coquillettidia linealis and Culex orbostiensis. There were no viruses isolated.

Batemans Bay: numbers were generally 'low' to 'moderate' throughout the season and well below the long-term average, although some ‘high’ numbers were trapped from the Council Depot. There were no viruses isolated.

Gosford: the number of traps this season was reduced to one (Empire Bay). Numbers tended to be ‘medium’ to ‘high’ and were well above average. Aedes vigilax dominated the Empire Bay collections. No viruses were isolated from any of the sites.

Newcastle: numbers were consistently ‘low’ from New Lambton, and ‘low’ to 'high' at Shortlands Wetlands, with large numbers of Aedes vigilax trapped in late March. No viruses were isolated.

Port Stephens: for most sites, mosquito numbers were around average for much of the season. However, ‘very high’ numbers were collected both very early and very late in the season from Heatherbrae, ensuring that overall numbers from Port Stephens were quite high. Aedes vigilax and Coquillettidia linealis dominated the collections. No viruses were isolated.

Tathra: mosquito numbers were below average and 'low'. No viruses were isolated.

Tweed Heads: both sites consistently yielded below average numbers for the season, with ‘low’ trap collections. No viruses were isolated.

Wyong: only one site, Ourimbah, undertook trapping this season. Numbers varied between ‘low’ and ‘high’, with Aedes notoscriptus being the species most commonly captured. No viruses were isolated.

METROPOLITAN SYDNEY. 8,906 mosquitoes, comprising 26 species, were collected from metropolitan Sydney. Aedes vigilax (31%), Aedes notoscriptus (15%) and Culex sitiens (15%) were the most common Sydney species.

Hawkesbury: collections were inconsistent and mainly ‘medium’ to ‘high’ in number. Culex quinquefasciatus and Aedes notoscriptus were the main species trapped. No viruses were isolated.

Parramatta: the insecticide treatments of Aedes vigilax breeding sites at Homebush Bay continued this season ensuring that the big collections of 1997-1998 were not repeated. Generally numbers were ‘low’ to ‘medium’, although there were some moderately large collections of Culex sitiens late in the season. No viruses were isolated.

Penrith: trapping was inconsistent this season due to a lack of a consistent dry ice supply. A new site of the ‘ADI’ was added, which is in the area where the cluster of RR cases occurred last season (Brokenshire et al., 2000). Numbers tended to be ‘high’ from the Sewerage Treatment Works, but mostly ‘low’ to ‘medium’ at the other sites. No viruses were isolated.

Ryde: like Parramatta, mosquito numbers were well down on 1997-98, due to the Ae. vigilax control program at Homebush Bay. Collections were 'low' to 'moderate' through most of the season, although Wharf Road (Site 1) had a series of 'high' collections through January to March. Aedes vigilax, Cx. sitiens and Ae. notoscriptus, were the most abundant species. No viruses were isolated.

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