The vulnerability of Australian horticulture to the Queensland fruit fly, Bactrocera (Dacus) tryoni, under climate change

The vulnerability of horticultural industries in Australia to the Queensland fruit fly Bactrocera (Dacus) tryoni under climate change is examined. Vulnerability is defined in terms of sensitivity and adaptation options. Regional estimates of fruit fly density are fed into an economic model that takes account of costs of damage, management, regulation and research. Sensitivity analyses are used to estimate potential future costs under climate change by recalculating costs with increases in temperature of 0.5 degrees C, 1.0 degrees C and 2 degrees C. It is assumed that irrigation will automatically compensate for any changes in rainfall. The current national, annual cost of Queensland fruit fly is estimated to be $AU28.5 million/year ($25.7-49.9 million), with 60% of the cost borne by commercial growers. Climatic warming threatens the sustainability of area freedom in the Fruit Fly Exclusion Zone (FFEZ) and is likely to increase damage and control costs to commercial growers in endemic areas, except in northern Australia. Costs to mainland apple, orange, and pear growers are estimated to increase by $3.1, $4.7, and $12.0 million with increases of 0.5 degrees C, 1.0 degrees C, and 2 degrees C, respectively. These represent increases of 25%, 38%, and 95%, respectively, but do not reflect the greatly increased risks of failure to maintain area freedom in the FFEZ. Growers in endemic Queensland fruit fly areas can expect their costs to increase 42-82%, compared with 24-83% in the FFEZ. Increased damage to backyard growers is likely, especially in South Australia and Victoria. Thus the fly poses a real threat to southern States under modest projected increases in temperatures. The extent of the likely cost increases raises questions about the industries' ability to pay and remain competitive. The current analysis illustrates the potential benefits of taking a national and strategic approach to the management of insect pests in Australia. A combination of CLIMEX modelling, sensitivity analysis and mapping provided valuable insights into both industry and regional vulnerabilities. Adaptation options require further quantification, but that awaits a credible population model of Queensland fruit fly. Costs need to be discounted, depending on the expected timing of the temperature increases.