Differences in climatic factors between Ross River virus disease outbreak and nonoutbreak years

Ross River virus is a common mosquito-borne arbovirus responsible for outbreaks of polyarthritic disease throughout Australia. To better understand climatic factors preceding outbreaks, we compared seasonal and monthly rainfall and temperature trends in outbreak and nonoutbreak years at four epidemic-prone locations. Our analyses showed that rainfall in outbreak years tended to be above average and higher than rainfall in nonoutbreak years. Overall temperatures were warmer during outbreak years. However, there were a number of distinct deviations in temperature, which seem to play a role in either promoting or inhibiting outbreaks. These preliminary findings show that climatic differences occur between outbreak and nonoutbreak years; however, seasonal and monthly trends differed across geo-climatic regions of the country. More detailed research is imperative if we are to optimize the surveillance and control of epidemic polyarthritic disease in Australia.

Is the potential of Coccidoxenoides perminutus, a mealybug parasitoid, limited by climatic or nutritional factors?

The encyrtid Coccidoxenoides perminutus is a widely distributed parasitoid of citrus mealybug (Planococcus citri). Worldwide, it has been implicated in successful biocontrol in only a few widely separated localities. C perminutus contributes little to control P. citri in field situations in south-east Queensland, Australia, but invades insectary cultures and reduces mealybug populations considerably under these controlled conditions. This discrepancy between poor field performance and good performance under controlled conditions was investigated to establish whether climatic factors inhibit the field performance of this species in the biological control of P. citri. Subsequent laboratory examination of the influence of varied humidities and temperatures on the activity levels and survival of C perminutus revealed a low tolerance for high saturation deficits (i.e., low % RH at high T degreesC) with reduced reproductive output. The influence of different food sources on adult survival and reproduction was also quantified, to establish if the adverse effects of climate could be overcome by supplementing adult diet. Neither honeydew from their mealybug hosts nor nectar from Alphitonia flowers significantly enhanced parasitoid survival. A subsequent test of five nectar species revealed a significant difference in their influence on C. perminutus survival and reproduction, with only Alpinia zerumbet proving to be as suitable as honey. The floral species that proved suitable in the laboratory need to be checked for their attractiveness to C perminutus in the field and for their ability to enhance the survival and reproductive output of parasitoids. This information suggests that the prevailing dry conditions in south-east Queensland citrus-growing areas apparently impede successful biological control of P. citri by C perminutus, but possibilities are available for habitat manipulation (by providing suitable nectar sources for adult parasitoids) to conserve and enhance C perminutus activity in the field. (C) 2004 Elsevier Inc. All rights reserved.

Effectiveness of evaporative cooling of beef cattle housed in confinement

Eighteen Angus steers exposed to high heat load conditions were used to assess the effectiveness of four spray cooling systems, on reducing the effects of heat load, the impact on microclimate and water usage. The steers were housed in groups of nine in a fully enclosed shed and were exposed to high heat load conditions for four days. The cooling systems used were water applied via a hose, via overhead sprinklers, via sprinklers at leg height and via misters. The water used was approximately 31 oC and contained 3% NaCl. Fans were used to ensure adequate air movement over the cattle. The animal parameters measured were feed intake, respiration rate, panting score and behaviour. Climatic factors were ambient temperature and wet bulb temperature. Ammonia levels were also measured. The hose, overhead sprinklers and misting were successful in reducing heat load on the cattle. The leg wetting system did not work because the dominant cattle blocked access to the sprinklers. The misting system used the most water (5483 L) and the hose the least (845 L). The application of water had minor impacts on wet bulb temperature, but resulted in significant reductions in dry bulb temperatures.

Ross River virus disease in Australia, 1886-1998, with analysis of risk factors associated with outbreaks

Ross River virus (RE) is a mosquito-borne arbovirus responsible for outbreaks of polyarthritic disease throughout Australia. To better understand human and environmental factors driving such events, 57 historical reports oil RR Outbreaks between 1896 and 1998 were examined collectively. The magnitude, regularity, seasonality, and locality of outbreaks were found to be wide ranging; however, analysis of climatic and tidal data highlighted that environmental conditions let differently ill tropical, arid, and temperate regions. Overall, rainfall seems to be the single most important risk factor, with over 90% of major outbreak locations receiving higher than average rainfall in preceding mouths. Many temperatures were close to average, particularly in tropical populations; however, in arid regions, below average maximum temperatures predominated, and ill southeast temperate regions, above average minimum temperatures predominated. High spring tides preceded coastal Outbreaks, both in the presence and absence of rainfall, and the relationship between rainfall and the Southern Oscillation Index and Lit Nina episodes suggest they may be useful predictive tools, but only ill southeast temperate regions. Such heterogeneity predisposing outbreaks supports the notion that there are different RE epidemiologies throughout Australia but also Suggests that generic parameters for the prediction and control of outbreaks are of limited use at a local level.