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As an adjunct to this, egg masses of Austropeplea were hatched out and reared in constant temperature rooms at 15°C, 25°C and 30°C with weekly changes of water and vegetation (Figure 9.5). Shell length was measured weekly until time of reproduction. At 15°C the snails grew slower but lived longer, but at 25°C and 30°C, there was little difference in growth rates, although those at 25°C were marginally larger at equivalent periods. Although water temperatures at the Ross River dam do occasionally drop to 16°C on occasions, generally they average 25–28°C (Hurley et al. 1995). Thus from this, an Austropeplea of 12 mm shell length collected during summer will be around one month old and capable of reproducing. One of 20 mm at either 25°C or 30°C water temperature would be approximately 100 days old. On this basis, it is suggested that monitoring could be comfortably done every two to three months. 9.6 Management options 9.6.1 General conclusions There are several other lakes, man-made or otherwise in northern Queensland, that support diverse recreational activities without apparent mishap. All are subjected to tropical conditions conducive to year round production of mosquitoes, snails, mites and pathogens. What is different about the Ross River dam stage 2A is its shallowness and proximity to large human populations. Nevertheless, the studies carried out in two blocks (1983–1987 and 1990–1995) have defined its mosquito and alphavirus hazard as considerable but no greater in the northern and north-eastern areas of Big Bay, Ti-Tree Bay, Round Island and Antill Creek than that experienced by local residents in everyday life. The relative hazard would change considerably, however, if the responsible local authorities ever decided to mount a broadscale aerial control programme against larval Aedes vigilax, which breed in the extensive intertidal wetlands. Restriction of activities to daylight hours will not only facilitate easier control of the public but will also reduce exposure to key vector species such as Culex annulirostris, Anopheles amictus and Aedes normanensis. However, who takes the responsibility for an estimated 5 billion mosquito larvae found periodically in the floating Hydrilla beds? As discussed, both Culex annulirostris and Anopheles annulipes are quite capable of dispersing from the reservoir into the urban populace. Recreational management issues are probably far less complicated than the moral issues. Whereas land clearance prior to the flooding of the stage 2A lake was effective in controlling tropical itch mites and some mosquito species, it also probably effected a redistribution of the kangaroos and wallabies, known to be most effective intermediate hosts of some arboviruses, including Ross River and the often fatal Murray Valley encephalitis. They have probably been driven towards the quieter eastern areas around Toonpan, where in 1992 Ross River virus was detected in wet season Aedes normanensis at rates as low as 1:217
DOI link for As an adjunct to this, egg masses of Austropeplea were hatched out and reared in constant temperature rooms at 15°C, 25°C and 30°C with weekly changes of water and vegetation (Figure 9.5). Shell length was measured weekly until time of reproduction. At 15°C the snails grew slower but lived longer, but at 25°C and 30°C, there was little difference in growth rates, although those at 25°C were marginally larger at equivalent periods. Although water temperatures at the Ross River dam do occasionally drop to 16°C on occasions, generally they average 25–28°C (Hurley et al. 1995). Thus from this, an Austropeplea of 12 mm shell length collected during summer will be around one month old and capable of reproducing. One of 20 mm at either 25°C or 30°C water temperature would be approximately 100 days old. On this basis, it is suggested that monitoring could be comfortably done every two to three months. 9.6 Management options 9.6.1 General conclusions There are several other lakes, man-made or otherwise in northern Queensland, that support diverse recreational activities without apparent mishap. All are subjected to tropical conditions conducive to year round production of mosquitoes, snails, mites and pathogens. What is different about the Ross River dam stage 2A is its shallowness and proximity to large human populations. Nevertheless, the studies carried out in two blocks (1983–1987 and 1990–1995) have defined its mosquito and alphavirus hazard as considerable but no greater in the northern and north-eastern areas of Big Bay, Ti-Tree Bay, Round Island and Antill Creek than that experienced by local residents in everyday life. The relative hazard would change considerably, however, if the responsible local authorities ever decided to mount a broadscale aerial control programme against larval Aedes vigilax, which breed in the extensive intertidal wetlands. Restriction of activities to daylight hours will not only facilitate easier control of the public but will also reduce exposure to key vector species such as Culex annulirostris, Anopheles amictus and Aedes normanensis. However, who takes the responsibility for an estimated 5 billion mosquito larvae found periodically in the floating Hydrilla beds? As discussed, both Culex annulirostris and Anopheles annulipes are quite capable of dispersing from the reservoir into the urban populace. Recreational management issues are probably far less complicated than the moral issues. Whereas land clearance prior to the flooding of the stage 2A lake was effective in controlling tropical itch mites and some mosquito species, it also probably effected a redistribution of the kangaroos and wallabies, known to be most effective intermediate hosts of some arboviruses, including Ross River and the often fatal Murray Valley encephalitis. They have probably been driven towards the quieter eastern areas around Toonpan, where in 1992 Ross River virus was detected in wet season Aedes normanensis at rates as low as 1:217
As an adjunct to this, egg masses of Austropeplea were hatched out and reared in constant temperature rooms at 15°C, 25°C and 30°C with weekly changes of water and vegetation (Figure 9.5). Shell length was measured weekly until time of reproduction. At 15°C the snails grew slower but lived longer, but at 25°C and 30°C, there was little difference in growth rates, although those at 25°C were marginally larger at equivalent periods. Although water temperatures at the Ross River dam do occasionally drop to 16°C on occasions, generally they average 25–28°C (Hurley et al. 1995). Thus from this, an Austropeplea of 12 mm shell length collected during summer will be around one month old and capable of reproducing. One of 20 mm at either 25°C or 30°C water temperature would be approximately 100 days old. On this basis, it is suggested that monitoring could be comfortably done every two to three months. 9.6 Management options 9.6.1 General conclusions There are several other lakes, man-made or otherwise in northern Queensland, that support diverse recreational activities without apparent mishap. All are subjected to tropical conditions conducive to year round production of mosquitoes, snails, mites and pathogens. What is different about the Ross River dam stage 2A is its shallowness and proximity to large human populations. Nevertheless, the studies carried out in two blocks (1983–1987 and 1990–1995) have defined its mosquito and alphavirus hazard as considerable but no greater in the northern and north-eastern areas of Big Bay, Ti-Tree Bay, Round Island and Antill Creek than that experienced by local residents in everyday life. The relative hazard would change considerably, however, if the responsible local authorities ever decided to mount a broadscale aerial control programme against larval Aedes vigilax, which breed in the extensive intertidal wetlands. Restriction of activities to daylight hours will not only facilitate easier control of the public but will also reduce exposure to key vector species such as Culex annulirostris, Anopheles amictus and Aedes normanensis. However, who takes the responsibility for an estimated 5 billion mosquito larvae found periodically in the floating Hydrilla beds? As discussed, both Culex annulirostris and Anopheles annulipes are quite capable of dispersing from the reservoir into the urban populace. Recreational management issues are probably far less complicated than the moral issues. Whereas land clearance prior to the flooding of the stage 2A lake was effective in controlling tropical itch mites and some mosquito species, it also probably effected a redistribution of the kangaroos and wallabies, known to be most effective intermediate hosts of some arboviruses, including Ross River and the often fatal Murray Valley encephalitis. They have probably been driven towards the quieter eastern areas around Toonpan, where in 1992 Ross River virus was detected in wet season Aedes normanensis at rates as low as 1:217
ABSTRACT