Post-Release Assessment of Aphalara Itadori (Hemiptera: Psyllidae) As a Classical Biological Control Agent of Fallopia Japonica (Polygonaceae)
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Post-release assessment of Aphalara itadori (Hemiptera: Psyllidae) as a classical biological control agent of Fallopia japonica (Polygonaceae) Gary D. Clewley Department of Life Sciences Imperial College London A thesis submitted for the degree of Doctor of Philosophy of Imperial College London June 2014 1 Declaration Except for the parts listed below, all work in this thesis is entirely my own and all references to other works are fully acknowledged. Chapter 5 - Emily Aldridge collected the data for the rainfall and plant quality experiments as part of her MSc thesis at Imperial College London. These works were carried out under my supervision and all analyses were my own. - Jennifer Hodgetts (Fera) carried out the molecular assays to detect A. itadori DNA using extractions I personally prepared and sent. Chapter 6 - Sarah Pierce (Imperial College London) carried out the nitrogen and phosphorous content assessment for the activated carbon samples. Signed Gary Clewley ‘The copyright of this thesis rests with the author and is made available under a Creative Commons Attribution Non-Commercial No Derivatives licence. Researchers are free to copy, distribute or transmit the thesis on the condition that they attribute it, that they do not use it for commercial purposes and that they do not alter, transform or build upon it. For any reuse or redistribution, researchers must make clear to others the licence terms of this work’ 2 Abstract Fallopia japonica is a damaging invasive weed that is difficult to control in the UK. In 2010, Aphalara itadori (Hemiptera), an insect herbivore native to Japan, was released in the UK as a biocontrol agent. Classical biocontrol of weeds has a long history across the world but this is an unprecedented type of release for the European Union. This provided the opportunity to investigate the conditions for establishment and the potential impacts of A. itadori under semi-natural conditions awaiting the potential establishment of large field populations in the UK. A meta-analysis, using global data, was carried out to see if classical biocontrol is an effective method of weed management. Field cage trials were then used to assess some life-history traits of A. itadori , including fecundity and longevity. Factors influencing establishment, including rainfall, competition and the role of generalist predators were investigated. The ability to cause damage to F. japonica is essential for a successful programme and this was tested, both directly and indirectly considering the performance of native plant species grown with F. japonica with and without biocontrol. Finally, the integration of biocontrol with existing control methods and preliminarily with another biocontrol agent, Mycosphaerella polygoni-cuspidati , a leaf-spot pathogen was investigated. Aphalara itadori showed the potential to be an effective biocontrol agent with the capacity to successfully reproduce outside, with potentially two generations per year in some areas of the UK. There were demonstrable impacts of A. itadori herbivory on F. japonica within a single growing season. Nonetheless, there was a discrepancy between the predicted performance from this study and what has been observed at the open field release sites. This is possibly a result of the effect of predation on A. itadori survival so recommendations, such as the use of protective cages, are suggested to inform the release strategy. 3 Acknowledgements Thanks go to my supervisors Prof Denis Wright and Dr Richard Shaw for their guidance and support throughout my PhD. I would like to thank CABI for hosting much of the research from this thesis and in particular all the staff that have assisted in any way, including Alex Brooks, Kate Jones, Suzy Wood , Kate Pollard, Marion Seier, Ghislaine Cortat and Tony Cross. I would especially like to thank René Eschen for his invaluable advice on all aspects of this work. Thanks go to the consortium of funders that have supported the biological control programme of Japanese knotweed. These are: CABI, The Department for Environment, Food and Rural Affairs, The Environment Agency, The Welsh Assembly Government, The South West Regional Development Agency, Network Rail, Cornwall Council and The Canals and Rivers Trust. This thesis was carried out on a studentship funded by the Biotechnology and Biological Sciences Research Council. Finally, thanks must also go to Prof Julia Koricheva (Royal Holloway University), Prof Simon Leather (Harper Adams University), Dr Nigel Straw (Forest Research), Sarah Pierce (Imperial College London), Emily Aldridge (Imperial College London), Helen Hipperson (Imperial College London), Louise Greenwood (Hart District Council) and Jennifer Hodgetts (FERA) for their advice or support. 4 Table of contents Chapter 1 Introduction 1.1 Invasion ecology 15 1.2 Classical biological control 18 1.3 Japanese knotweed 22 1.4 Aims and objectives 28 Chapter 2 General materials and methods 2.1 Plants 30 2.2 Insects 30 2.3 Study sites 31 2.4 Statistical analyses 32 Chapter 3 The effectiveness of classical biological control of invasive plants 3.1 Introduction 33 3.2 Materials and methods 3.2.1 Literature search 35 3.2.2 Data extraction 36 3.2.3 Statistical analysis 38 3.3 Results 39 3.4 Discussion 45 Chapter 4 Life history 4.1 Introduction 50 4.2 Materials and methods 4.2.1 Development and thermal requirements 54 4.2.2 Fecundity and longevity 55 5 4.2.3 Overwintering 55 4.3 Results 4.3.1 Development and thermal requirements 57 4.3.2 Fecundity and longevity 57 4.3.3 Overwintering 58 4.4 Discussion 60 Chapter 5 Establishment factors 5.1 Introduction 5.1.1 Release conditions 64 5.1.2 Species interactions 66 5.2 Materials and methods 5.2.1 Release conditions 69 5.2.2 Species interactions 70 5.2.3 Predicting establishment rates 73 5.3 Results 5.3.1 Release conditions 73 5.3.2 Species interactions 75 5.3.3 Predicting establishment rates 79 5.4 Discussion 5.4.1 Release conditions 80 5.4.2 Species interactions 82 Chapter 6 Impacts 6.1 Introduction 6.1.1 Direct target impacts 87 6.1.2 Indirect impacts 88 6.2 Materials and methods 6.2.1 Direct target impacts 90 6.2.2 Indirect impacts 91 6.3 Results 6 6.3.1 Direct target impacts 93 6.3.2 Indirect impacts 95 6.4 Discussion 6.4.1 Direct target impacts 97 6.4.2 Indirect impacts 100 Chapter 7 Integration of management methods 7.1 Introduction 7.1.1 Conventional management 103 7.1.2 Multiple biocontrol agents 105 7.2 Materials and methods 7.2.1 Conventional management 107 7.2.2 Multiple biocontrol agents 110 7.3 Results 7.3.1 Conventional management 111 7.3.2 Multiple biocontrol agents 116 7.4 Discussion 7.4.1 Conventional management 117 7.4.2 Multiple biocontrol agents 120 Chapter 8 General discussion 8.1 Key findings 122 8.2 Discussion 124 References 128 Appendices 161 7 Tables and figures Table 1.1 Common synonyms of F. japonica . Information taken from CABI Invasive Species Compendium and Bailey & Conolly (2000). 23 Table 3.1. Heterogeneity (Q total ) for each variable of observed effect sizes from studies of the impact of biocontrol on invasive plants. N increase and N decrease refer to the number of studies with an effect size in a particular direction between the treatment group relative to the control. Native species data was a subset of non-target species. 40 Table 3.2. Heterogeneity (Q between ) between different study characteristics considered to explain variation in each meta-analysis of the impact of biocontrol of invasive plants. Characteristics are invasive region (continental scale), native region (continental scale), feeding guild or attack mode and taxa of the biocontrol agent and the growth form (defined using the USDA growth habit definitions), longevity (annual, biennial or perennial) of the target plant and the study duration. Significant results are in boldface. 44 Table 4.1 Mean ± SE duration (days) development for different life stages of A. itadori at various constant temperatures in °C ( - indicates no development occurred). Values presented from Myint et al. (2012) are for females only. N1-5 refers to nymphal instars. 52 Table 4.2. Fecundity and longevity of A. itadori placed outside between May and October 2012 (n=26). Mated pairs were placed on individually sleeved F. Japonica plants . Eggs were counted and plants were replaced weekly. 58 Table 5.1. Observations of generalist predators occurring on F. japonica plants with A. itadori under the unprotected control treatment outside in a garden environment between May and July 2013. 77 Table 5.2. Mean, minimum and maximum temperatures (°C) recorded using four DS1921G-F5 thermochron dataloggers at each of the release sites over an 8 week period between May and July 2013. 78 8 Table 5.3. CT values (mean of two runs from each sample) from preliminary assays to detect A. itadori DNA from the contents of a generalist predator, A. nemorum , either fed or not fed psyllid under control conditions. Two extraction methods, PCR probes and predator number were trialled. A cut-off of C T < 38 was marked positive and are indicated in bold. 79 Table 5.4. Summary of the percentage difference of the number of A. itadori between some of the different conditions of the establishment factors investigated. 86 Table 6.1. Table summarising the analyses of plant growth measurements of Fallopia japonica exposed to an initial density of 50 adult Aphalara itadori per plant. Insects were left to develop unhindered for 14 weeks before sampling. All plants were housed outside in field cages under near-normal environmental conditions. 93 Table 6.2. Impact of sleeves on performance of F. japonica grown in a field cage for 14 weeks.