Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the pennission of the Author. THE POTENTIAL ABILITY OF Stethorus bifidus (Kapur) TO REGULATE POPULATIONS OF Tetranychus lintearius (Dufour) A Thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Ecology at Massey University. PAUL GORDON PETERSON 1993 PLATE 1: Gorse as a problem in forestry KOPURIKI NEAR TE PUKE Silviculture practices are restricted or prevented by gorse. ii ABSTRACT Tetranychus /intearius Dufour (Acari; Tetranychidae) was released in New Zealand, in 1989, to assist in the regulation of gorse ( Ulex europaeus). The present study was initiated to determine why colonies of GSM are consistently failing to establish above parallel 39° S and the possibility that Stethorus bifidus may be regulating populations of T.lintearius (GSM). Predation by S.bifidus was investigated by examining both numerical and functional responses to prey density. - Development of S.bifidus is described by a linear relationship with temperature between 8.5°C and 27.5°C (numerical response). Oviposition and temperature are linearly related and independent of GSM density. Measurements of temperature under GSM webbing showed an elevation of 1- 20 C above ambient. - The feeding rate of S.bifidus increased in a non-linear fashion between 6.5°C and 32.5°C (functional response). - Handling time decreased with increasing prey density demonstrating that S.bifidus is an effective predator at high mite densities. This investigation suggests that the role of S.bifidus in regulating GSM is more important in northern regions of New Zealand. iii ACKNOWLEDGEMENTS I would firstly like to thank my supervisor Professor B.P.Springett for his guidance and support during the planning, execution and writing up of this thesis. In particular I am grateful to Prof. Springett for time spent fine-tuning written work for final presentation. P.McGregor, Landcare, C.R.I., Palmerston North offered constructive criticism and undivided attention throughout the year. Help with statistical analysis was extensively provided by P.McGregor whose endless patience and support was invaluable. Mite identification was carried out by G.Ramsay, and help in identifying Stethorus species was provided by J.Charles, both of who work at the Mt. Albert Research Centre. A.Hill who engineered the topic helped to initiate early work with suggestions and encouragement. This included hints for experimental set up and mite rearing in particular. I would also like to thank C.Winks for taking time to show me a GSM release site at Albany. I am grateful to Jens Jorgensen for the construction of feeding cell pads and help with humidity chamber construction. Finally I would like to thank my parents for their moral support and Miranda for her encouragement and patience. TABLE OF CONTENTS PAGE Abstract. ................................................................................................ ii Acknowledgements ............................................................................... iii Table of Contents ................................................................................. iv List of Plates ......................................................................................... vi List of Tables ........................................................................................ viii List of Figures ....................................................................................... ix Chapter one - Introduction .................................................................... 1 Chapter two - Biology and Life History of Tetranychus lintearius ... 13 Chapter three - Biology and Life History of Stethorus bifidus ......... 26 Chapter four - The Predatory Ability of Stethorus bifidus................. 45 Part one: The Reproductive Response ............................................ 45 (A component of the numerical response) Part two: Components of the Functional Response General Introduction ...................................................... 73 Section one: Feeding rate of Stethorus bifidus......... 74 Section two: Handling time ........................................... 84 Chapter five - Discussion ....................................................................... 93 V Chapter six - Summary .......................................................................... 109 Appendices ............................................................................................ 111 References/Bibliography ...................................................................... 118 vi LIST OF PLATES 1: Gorse as a problem in forestry .............................................................. I 2: Tetranychus lintearius the biocontrol agent.. ...................................... 4 a- mid range b- close range c- electron micrograph 3: GSM feeding damage to gorse ............................................................ 15 4: Phytoseiulus persimilis a predatory mite that feeds on GSM ........... 24 5: GSM web interfering with predator mobility? ..................................... 32 a- a barrier to beetle larvae b- however rarely restricting adults 6: The coccinellid Stethorus bifidus.......................................................... 41 7: Beetle egg laid amongst GSM eggs ...................................................... 49 8: Developmental stages of Stethorus bifidus.......................................... 50 a- egg with eye spots b- 1st instar c- 2nd d- 3rd e- 4th f- pupa 9: Probe used to measure temperature under GSM web ......................... 56 1O: 'Cell pad' used for feeding tests ........................................................... 76 vii 11: a- Stethorus bifidus feeding on an adult GSM ............................... 86 b- Mites attacked by beetles of differing hunger states ................ 86 viii LIST OF TABLES 1: A comparison of development rates of S.bifidus in cells and on shoots ............................................................................................... 55 2: Threshold temperatures for development of Stethorus bifidus.......... 57 3: GSM establishment success in relation to temperature ...................... 65 4: b- Maximum feeding rate of Stethorus blfldus in relation to temperature ....................................................................................... 79 c- Humidity readings ........................................................................ 79 5: Indices of extraction ................................................................................. 88 6: Exogenous population processes responsible for population regulation ........................................................................................... 95 7: Comparative development rates of a- Tetranychus llntearius in relation to temperature .................... 100 b- Stethorus bifidus in relation to temperature ............................. 100 ix LIST OF FIGURES 1: Development rate of Stethorus bifidus In relation to temperature a- preimaginal stages .................................................................... 58 b- total development. ..................................................................... 60 2: Oviposition of Stethorus bifidus in relation to a- GSM density between 11.5°C and 32.5°C ................................ 62 b- temperature ................................................................................. 64 3: GSM establishment success in relation to temperature .................... 66 4: a- Effect of GSM webbing on temperature ................................... 68 b- temperature under GSM web in relation to temperature on gorse................................................................................................. 69 5: Consumption by S.bifidus in relation to a- GSM density................................................................................. 80 b- temperature .................................................................................. 82 6: Stethorus bifidus prey density determining handling time ................ 89 7: Major body divisions of the Acari. ....................................................... 91 8: Factors determining the predatory potential of Stethorus bifidus... 98 9: Comparison of development rates of Stethorus bifidus and Tetranychus lintearius in relation to temperature ....................... 101 CHAPTER ONE: INTRODUCTION Part one: Regulation of gorse in New Zealand - The plant, the biocontrol agents, the policies/procedures and the complications. Gorse - The options for regulation of a noxious plant: Gorse ( U!ex europaeus L.) is a fast growing woody legume capable of establishing rapidly from seeds or stumps. It thrives particularly in low fertility soils where the competitive ability of other 'more favoured' plants is reduced. Although gorse is found throughout Europe, it is only considered a major weed of agriculture and forestry in North America, South Australia, Tasmania, New Zealand and at high altitudes in Hawaii. A warm, moist climate free of temperature extremes and exposure to cold winds appears to suit gorse. Control is difficult and expensive. In 1977, chemical control of gorse in New Zealand cost approximately $7 million and this did not include the cost of lost production (Maccarter & Gaynor 1980). According to Miller (1970; cited in Hill & Gourlay 1990),