OVER-WINTERING ECOLOGY OF LUCILIA CUPRINA IN SOUTH-EASTERN AUSTRALIA Sandra De Cat, BVSc Submitted in total fulfilment of the requirements of the degree of Master of Veterinary Science June 2007 University of Melbourne School of Veterinary Science ii ABSTRACT Flystrike is a major problem for the Australian sheep industry, estimated to cost at least $280 m annually. A review of blowfly strike and the ecology of the primary sheep blowfly (Lucilia cuprina) in south-eastern Australia revealed that some aspects of the biology of L.cuprina were still poorly understood. In addition, no recent studies had been conducted in Western Victoria, a high winter rainfall area with a large population of Merino sheep. Consequently, a 2-year study on the seasonal timing of larval over-wintering and spring emergence of flies was undertaken on a farm near Ballarat, in Western Victoria, during 2005 and 2006. Replicated cohorts of postfeeding larvae of L.cuprina were deposited regularly, and the daily emergence of flies and meteorological observations were recorded. Larvae deposited during spring, summer and early autumn developed rapidly, with the time to median emergence of flies taking 30 days in spring, decreasing to 10 days as soil temperatures increased in summer. A transitional phase of larval development was observed during mid-autumn of both years (11-26 April), slightly later than in a previous study at Canberra. Some larvae deposited in this period pupated immediately, whereas others entered an arrested development, emerging as flies the following spring. Induction of this arrested development was associated with sustained low soil temperatures (≤ 10oC). In both years, over-wintering larvae resumed their development in late winter after soil temperatures exhibited a rising pattern or consistently stayed above 11oC. The mean dates for the first and median emergence of flies in spring were 4 and 21 October in 2005, and 1 and 12 October in 2006, respectively. This emergence of flies from over- wintering larvae was synchronous, regardless of the date larvae were deposited. Mortality of over-wintering larvae was high, although quite variable between deposits, being 95% in 2005 and 68% in 2006. Sequential sampling of larvae deposited in May 2006 indicated that pupation of over- wintering larvae occurred between 29 August and 14 September. Trapping of free- i ranging flies at the site found that fly numbers followed a bimodal pattern, with a large peak in November and a smaller peak in early March. Validation of six predictive models of L.cuprina development, using data from this study, showed none could predict the last generation of flies in autumn, the time when larvae entered arrested development, or the occurrence of a split emergence. A simple linear model (‘Temsum’), using actual soil temperatures and 1 July as start date, was best able to predict the first generation of flies in spring. Ecological studies such as this will help to refine Integrated Parasite Management (IPM) programs for the control of flystrike. A number of aspects of L.cuprina biology were identified that deserve further study, in particular the development of immature stages at low temperatures. This information would also support the development of more complex models simulating the population dynamics of L.cuprina. ii DECLARATION This is to certify that: (i) this thesis comprises only my original work, (ii) due acknowledgement has been made in the text to all other material used, (iii) no part of this thesis has been submitted for any other degree. Sandra De Cat iii The Lord in His wisdom made the fly, And then forgot to tell us why. Ogden Nash 1902-1971 v ACKNOWLEDGEMENTS Two and a half years ago, my passion for sheep drew me to Australia. Little did I know that I would be looking at maggots and flies instead of the red dirt and woolly sheep I had fantasized about. This research opened my eyes and helped me realize that science is a fascinating and never-ending journey. I would love to take this opportunity to thank a few people who guided me on this trip. Firstly, I wish to thank my supervisors, Dr John Larsen and Dr Norman Anderson for their supervision, advice and teaching throughout this study in addition to their patience and assistance with the writing of this thesis. I also thank Garry Anderson and Brian Horton for their statistical advice and generous assistance in validating the models. Many thanks to Jim and Betty Boyle, property owners of “Woodside”, and Dale Woods, the property manager, for the daily inspections of the field pots. Without Dale’s dedication, this valuable data would never have been collected. Also thanks to Dianne Rees, who assisted me with the field work and spent several hours with me sifting soil. I would also like to thank Ayscha Hill-Williams, technical officer at the University of Melbourne, Department of Genetics, for rearing the larvae and maintaining my flies for the duration of this study. I am very grateful for receiving an IPRS and MIRS scholarship from the University of Melbourne, as well as extra funding from Australian Wool Innovation, as part of their Integrated Parasite Management (IPM)-sheep project. Thanks to all the staff of the Mackinnon Project and my friends in Melbourne. They made me feel at home and helped me out in any way possible. The little day to day kindness of the people of Melbourne is something I will cherish for the rest of my life. Finally, I would like to thank my parents and sister for supporting me in every way during this great Australian adventure. They mean the world to me! vii viii TABLE OF CONTENTS Abstract...........................................................................................................................i Declaration....................................................................................................................iii Acknowledgements......................................................................................................vii Table of Contents .........................................................................................................ix List of Tables ...............................................................................................................xii List of Figures............................................................................................................. xiv Chapter 1 Literature Review ......................................................................................... 1 1.1 Development of Sheep & Wool Production in Australia................................................. 1 1.2 Blowflies in Australia ............................................................................................................. 2 1.3 Identification of Lucilia cuprina.............................................................................................. 3 1.3.1 Adult Flies ...................................................................................................................... 3 1.3.2 Larval & Pupal Stages................................................................................................... 3 1.4 Life Cycle of L.cuprina............................................................................................................ 5 1.4.1 Egg Stage ........................................................................................................................ 5 1.4.2 Larval Stages................................................................................................................... 5 1.4.2.1 Larval Feeding Stage............................................................................................ 5 1.4.2.2 Postfeeding Larval Stage ..................................................................................... 6 1.4.3 Pupal Stage ..................................................................................................................... 7 1.4.4 Adult Stage ..................................................................................................................... 7 1.4.4.1 Emergence............................................................................................................. 7 1.4.4.2 Nutritional Requirements.................................................................................... 7 1.5 Dormancy among Blowflies ................................................................................................. 8 1.6 Dormancy in L.cuprina ........................................................................................................... 9 1.7 The Distribution & Abundance of L.cuprina Flies...........................................................10 1.7.1 Oviposition...................................................................................................................10 1.7.2 Dispersal of Flies.........................................................................................................11 1.7.3 Seasonal Abundance ...................................................................................................12 1.8 Blowfly Strike in Merino Sheep..........................................................................................13 1.8.1 Breech Strike ................................................................................................................13 1.8.2 Body Strike ...................................................................................................................14 1.8.3 Other Strikes ................................................................................................................14