THERMAL PHYSIOLOGY AND PREDICTED DISTRIBUTION OF ZYGOGRAMMA BICOLORATA (CHRYSOMELIDAE), A PROMISING AGENT FOR THE BIOLOGICAL CONTROL OF THE INVASIVE WEED PARTHENIUM HYSTEROPHORUS IN SOUTH AFRICA HELEN KING Submitted in fulfilment of the academic requirements for the degree of MASTER OF SCIENCE in the Discipline of Entomology School of Biological and Conservation Sciences Faculty of Science and Agriculture University of KwaZulu-Natal Pietermaritzburg 2008 i PREFACE The experimental work described in this dissertation was carried out in the School of Biological and Conservation Sciences, University of KwaZulu-Natal, Pietermaritzburg and at the Cedara Weeds Unit (ARC – Plant Protection Research Institute) from January 2006 to January 2008, under the supervision of Doctor Terence Olckers and co- supervision of Doctor Andrew McConnachie and Professor Colleen Downs. This dissertation, submitted for the degree of Master of Science in the Faculty of Science and Agriculture, University of KwaZulu-Natal, Pietermaritzburg, represents original work by the author and has not otherwise been submitted in any form for any degree or diploma to any University. Where use has been made of the work of others, it is duly acknowledged in the text. …………………………. Helen King January 2008 I certify that the above statement is correct ………………………….. Doctor Terence Olckers Supervisor ………………………….. Doctor Andrew McConnachie Co-supervisor ………………………….. Professor Colleen T. Downs Co-supervisor January 2008 i ii ABSTRACT Parthenium hysterophorus (Asteraceae), classified as an emerging weed in South Africa, has become abundant throughout large parts of southern and eastern Africa. In South Africa it has invaded areas in KwaZulu-Natal, Mpumalanga, the North West Province and Limpopo. A biological control programme against parthenium weed was launched in South Africa in 2003, based on the success achieved in Australia. Zygogramma bicolorata, a leaf-feeding beetle native to Mexico, was imported into South Africa via Central Queensland, Australia where it was released in the 1980s. This thesis examines aspects of the thermal physiology of Z. bicolorata which, in conjunction with its native and exotic geographical distribution, was used to predict the potential distribution of the agent in South Africa, in relation to climate. To determine Z. bicolorata’s physiological capability, several physiological parameters were examined for mechanistic modelling purposes. These parameters included the beetle’s lethal thermal limits, critical thermal limits, lethal humidities (Chapter 2) and developmental rate at constant temperatures (Chapter 3). In Chapter 4, these physiological parameters were entered into the dynamic modelling program CLIMEX (CLIMEX programme ver. 2, CSIRO Entomology ©) and a map of the areas that are acceptable for the establishment of Z. bicolorata was produced. The CLIMEX model predicted that most of South Africa is favourable for the establishment of the beetle, except in the west of the country and in the north of Lesotho, extending into South Africa. All areas in which parthenium currently occurs were predicted to be very favourable for Z. bicolorata establishment and proliferation. Optimal release sites aimed at initial establishment were earmarked at three areas in the northeastern part of South Africa (Jozini, Ndumu Game Reserve and along the road from ii iii Swaziland to Mozambique). It is concluded that Z. bicolorata is climatically suited to South Africa, increasing the likelihood that populations will establish and proliferate when released. Keywords: CLIMEX, distribution, Parthenium hysterophorus, South Africa, thermal physiology, Zygogramma bicolorata iii iv ACKNOWLEDGEMENTS I thank my three supervisors, Dr Terence Olckers, Dr Andrew McConnachie and Prof. Colleen Downs. Having three supervisors so generous with their time and so eager to be of help was a blessing. To everyone who gave me advice, help and ideas I am exceptionally grateful. I extend a special thank you to Craig Morris, for sharing his statistical genius and Dr Alec McClay and Dr Rachel McFadyen, for supplying me with unpublished data from Mexico and Australia respectively. To my family, thank you for helping me in the lab. at the crack of dawn on Saturday mornings, feigning interest when I spoke of work and for taking the readership of this dissertation into double figures. I could not wish for a better family. Thank you to Barry for always being so understanding and kind when my stress led to grumpiness, I promise I don’t get much worse. Thank you to the ARC – PPRI for allowing me to utilize their facilities, and to all the scientists for always being helpful, friendly and generous with their equipment. I hope you find this work helpful in your endeavour to control parthenium in South Africa. Finally, I am exceedingly grateful to the Working for Water Programme (Department of Water Affairs and Forestry) for supplying the funding for this MSc. iv v CONTENTS PREFACE..................................................................................................................... i ABSTRACT................................................................................................................. ii ACKNOWLEDGEMENTS........................................................................................... iv CHAPTER 1 INTRODUCTION 1.1. INVASIVE ALIEN PLANTS................................................................................ 1 1.2. BIOLOGICAL CONTROL OF WEEDS................................................................ 3 1.3. PARTHENIUM HYSTEROPHORUS ..................................................................... 4 1.4. CHEMICAL AND MECHANICAL CONTROL OF PARTHENIUM.................... 6 1.5. BIOLOGICAL CONTROL OF PARTHENIUM.................................................... 7 1.5.1. Biology of Zygogramma bicolorata .......................................................... 8 1.5.2. Host-specificity of Zygogramma bicolorata .............................................. 10 1.6. PROJECT BACKGROUND AND AIMS............................................................... 11 1.6.1. Factors limiting establishment and success of biocontrol agents................. 11 1.6.2. Objectives of study.................................................................................... 12 CHAPTER 2 PHYSIOLOGICAL LIMITS OF ZYGOGRAMMA BICOLORATA 2.1. INTRODUCTION................................................................................................. 14 2.1.1. Parthenium in South Africa........................................................................ 14 2.1.2. Climatic limitations of ectothermic agents.................................................. 15 2.1.2.1. Critical Thermal Maxima and Minima ....................................... 18 2.1.2.2. Lethal Thermal Limits ................................................................. 19 2.1.2.3. Lethal Humidities ....................................................................... 20 2.1.3. Aims......................................................................................................... 22 v vi 2.2. METHODS............................................................................................................ 22 2.2.1. Insect cultures........................................................................................... 22 2.2.2. Critical thermal limits................................................................................ 23 2.2.3. Lethal temperatures................................................................................... 24 2.2.4. Lethal humidities....................................................................................... 26 2.2.4.1. Effect on egg hatch ..................................................................... 26 2.2.4.2. Effect on pupation and adult emergence ..................................... 26 2.3. RESULTS.............................................................................................................. 27 2.3.1. Critical thermal limits................................................................................ 27 2.3.2. Lethal limits.............................................................................................. 28 2.3.3. Lethal humidities....................................................................................... 30 2.4. DISCUSSION........................................................................................................ 32 CHAPTER 3 DEVELOPMENTAL RATE AND DEGREE-DAY MODELLING 3.1. INTRODUCTION................................................................................................. 40 3.1.1. Developmental limitations of ectotherms................................................... 40 3.1.2. Developmental rate................................................................................... 41 3.1.3. Degree-day model..................................................................................... 42 3.1.4. Aims......................................................................................................... 42 3.2. METHODS............................................................................................................ 43 3.2.1. Insect culture............................................................................................ 43 3.2.2. Developmental rate................................................................................... 43 3.2.3. Degree-day model....................................................................................