University of Tasmania
Benedetti_Vallenari_whole_thesis.pdf (1.36 MB)

The development of a model for flystrike resistance management

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posted on 2023-05-27, 23:56 authored by Benedetti Vallenari, PF
Flystrike is of major concern to the Australian sheep industry, with the Australian sheep blowfly (Lucilia Cuprina) demonstrating the ability to develop resistance to commonly used insecticides. Over time, chemical and non-chemical strategies have been recommended to sheep producers to manage resistance development, mainly the rotation of chemical groups. Literature regarding the effectiveness of chemical rotations is sparse, with the consensus that rotations should be implemented without confidence in which type of rotation strategy is best. Similarly, producers are advised that non-chemical strategies such as shearing and/or crutching during the flystrike season and monitoring the flock for signs of flystrike are worthwhile flystrike management strategies with little knowledge of how these strategies influence flystrike resistance development. The aim of this study was to develop and utilise a computer model to evaluate the effects of rotations, monitoring, and shearing or crutching on resistance development in various resistance genes. The data collected from the model was then used to assess the current advice given to producers regarding flystrike resistance management on the FlyBoss website. The model consisted of various assumptions and settings that were tested for their functionality and importance. Then various rotation, shearing and crutching simulations were run for periods of 20 or in some cases 50 years, with and without a genetic disadvantage for genes for resistance. Increasing routine monitoring or implementing extra monitoring were tested to explore the effect of monitoring on resistance development and reduction in flystrike related costs. All rotations simulated delayed the onset of resistance development and were more cost-effective than using any insecticide continuously. Shearing in spring, summer or autumn proved more cost-effective than shearing in winter, although shearing in summer increased the rate of resistance development. Similarly, including a crutching in spring, summer or autumn also proved more cost-effective than not crutching, with summer crutching increasing the rate of resistance development. Evaluating monitoring was more complex, with the cost of labour being an important factor in determining the cost-effectiveness of implementing a higher frequency or more intense monitoring. More intense monitoring, or the physical or chemical killing of flies on the struck sheep, reduced the rate of resistance development. The advice given in FlyBoss was regarded as partially incomplete, with areas regarding the impact of flystrike management strategies on flystrike resistance development requiring elaboration


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