Economic assessment of preparedness strategies to prevent the introduction or the permanent establishment of screwworm fly in Australia

Abstract

A bio-economic model is used to evaluate 12 alternative preparedness strategies for combating a potential invasion of Australia by the Old World screwworm fly (SWF), Chrysomya bezziana Villeneuve. The expected total costs of maintaining the strategies are derived over a 30 year economic planning horizon using both direct producer losses (based on constant prices) and changes in the combined producer and consumer surplus (economic surplus). The latter approach accounts for both producer and consumer welfare effects of an invasion. Based on direct producer losses, the least-cost strategy is to build a shared (50% devoted to SWF eradication) multi-insect eradication facility (with a total production capacity of 100 million sterile flies per week) in Australia prior to an invasion, with the maintenance of an overseas seed colony. This conclusion is based on an annual joint probability of entry and successful establishment of the fly in Australia of 1 in 325 years or higher. However, when the annual probability of successful invasion is reduced below 1 in 325, the optimal strategy is the prior design of a 150 million flies per week capacity factory and waiting for an invasion before building that factory. At a probability level below 1 in 1250, the optimal strategy is to wait for an invasion and then build a factory with the capacity to produce in the range of 200 to 250 million flies per week. When changes in economic surplus are used to measure societal losses of a SWF invasion, the optimal strategies remain the same but at different levels of annual probability of successful invation. The shared multi-insect eradication facility with a capacity of 100 million flies per week is the optimal strategy at an annual probability level of 1 in 516 or higher. A prior design of a 150 million flies per week capacity factory and waiting for an invasion before building that factory dominates all other strategies at an annual probability level between 1 in 516 and 1 in 2500. At a probability level of 1 in 2500 or lower no additional preparedness activity is required until the occurrence of an invasion.