The Influence of a Carabid Beetle Predator on the Behaviour and Dispersal of Slug Pests Clare Gillian Armsworth B.Sc. A BBSRC Studentship Research was conducted at the Plant and Invertebrate Ecology Division, Long Ashton Research Station and Rothamsted Research. A dissertation submitted to the University of Wales, Cardiff, in accordance with the requirements of the degree of Doctor of Philosophy in the Faculty of Science. May 2005 Words - 49902 UMI Number: U584702 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI U584702 Published by ProQuest LLC 2013. Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 Abstract It is becoming increasingly recognised that natural enemies in arable land, particularly polyphagous predators such as carabid beetles, may help to suppress populations of pests, and that appropriate management of such predators may lead to a satisfactory level of pest control. Previous work has shown that a polyphagous carabid predator, Pterostichus melanarius, is capable of affecting the spatial and temporal dynamics of slug pest populations. This project is an examination of how P. melanarius affects the survival, behaviour and dispersion of two important slug pests, Deroceras reticulatum and Arion intermedius, and how this information applies to spatial and temporal data previously obtained from the field. Deroceras reticulatum, but not Arion intermedius, elicited a variety of anti-predator behaviour in the presence of substrates previously exposed to the predator. The movements of slugs in arenas, incorporating a zone containing paper upon which the predatory beetles had previously been maintained and a control zone, were recorded at intervals. Significantly more slugs of all the size classes tested accumulated on the control half of arenas after 24 hours, with small slugs being quickest to respond. Slugs avoided paper exposed to both male and female beetles. Slugs also avoided paper exposed to another predatory carabid, Pterostichus madidus, but not to Harpalus affinis, a phytophagous carabid. Slugs did not respond to paper that had been exposed to beetles and then stored for five days prior to the test. Changes in parameters of movement of slugs when in the presence of P. melanarius chemicals were detected using a video-tracking system. These changes are consistent with a kinesis that would enable slugs to rapidly escape from areas where beetles were recently present. Despite this no changes in the rate of dispersion of D. reticulatum juveniles was detected in mini-plots previously exposed to P. melanarius. However, adult D. reticulatum reduced feeding and egg-laying and increased refuge on soil previously exposed to P. melanarius. Chemicals on the exterior of P. melanarius were isolated and two compounds were found to reduce feeding by D. reticulatum on leaf discs compared to control discs. One of these chemicals is currently being analysed using mass spectroscopy and NMR to determine it's structure and identity. It was concluded that D. reticulatum have evolved behavioural responses to chemical cues from either this generalist carabid predator in particular, or carabid beetles generally, many species of which include molluscs in their diets. ii During a video-tracking study of beetle movements, some evidence was found for the detection and response of beetles to slug mucus, and amputation work suggested that the palps may be important in slug detection. Previous feeding experience was found not to influence prey choice in P. melanarius during a food choice experiment, with beetles always selecting a mixed diet when offered. Analysis of spatial data showed that slug size, but not beetle sex, was important in the spatial relationship between the predator and the prey, and this agrees with results from the laboratory experiments of slug behaviour. This work has added to the evidence provided by other studies that some generalist predators can have significant effects on the dynamics of pest populations and therefore may become useful biocontrol agents for pests if effectively managed. The implications of this work in the field of predator-prey ecology and for the efficacy of P. melanarius as a biological control agent of slugs are discussed. Acknowledgements There are many people who have contributed to this project and to my personal well-being over the last three years. It will be difficult to try and thank everybody but I shall attempt to as best I can. Firstly of course I would like to express my gratitude to the Biotechnology and Biological Sciences Research Council for providing the funding to enable me to carry out this research. I would also like to thank my three supervisors. You all showed a lot of confidence in me and were always there when I needed help. In particular I thank Prof. David Glen for all the help he gave me, especially in my first year when I started out at Long Ashton and for regularly posting me slugs in my third year, they were very gratefully received! I want to thank Dr. Bill Symondson, although I never worked at Cardiff directly under his supervision, he was always there for me, all his help and advice was really appreciated. Finally I would like to send a big thank you to Dr. David Bohan, he has helped me immensely during my work. He was very encouraging and was always available when I needed advice. I would like to thank all the people I worked with and socialised with at the Long Ashton Research Station. I had a wonderful first year there and miss it a lot. In particular I want to thank the greenhouse staff who helped me with all my mini-plot experiments. I want to express my appreciation to the people who helped me at Rothamsted, especially to the people in the PIE division for creating such a nice working atmosphere and all the general help and advice I received. In particular I want to thank Colin Alexander and Kelvin Conrad for helping me learn how to get to grips with SADIE; Hasse Rasmussen, Mike Birkett and Tony Hooper in the BCH division for collaborating with me on the biochemistry work and thanks also to Albert Callewaert, Steve Harvey and other members of the greenhouse team for helping me set up mini-plots, grow cabbages etc. Finally a very special thank you to Steve Powers for all his help on statistics over the entirety of the last three years, he never turned me away when I needed advice, and that was quite frequently! I want to thank Kit and Carina for putting up with me always coming around in the first year and Dave and Claire for putting a roof over my head when I first came to Rothamsted. I also want to thank all the girls: Sam, Femke, Inez, Jenna and Louise for all the iv fun and giggles over the past two years but also their emotional support, I am going to miss you so much. A big thank you goes to my parents who have always been there for me, supported and believed in me, it really means a lot. Last but not least I want to send a huge thank you and a lot of love to my wonderful partner Mike, to whom I dedicate this thesis. You have helped me through thick and thin and always been there for me, it's impossible to thank you enough for all your love and support. Author's declaration This work has not previously been accepted in substance for any degree and is not being concurrently submitted in candidature for any degree Signed.. __ ................................................. ............(candidate) Date .'Z r ................................ This thesis is the result of my own investigations, except where otherwise stated. Other sources are acknowledged by footnotes giving explicit references. A bibliography is appended. Signed............................rvr? .................................... (candidate) Date........... I hereby give consent for my thesis, if accepted, to be available for photocopying and for inter-library loan, and for the title and summary to be made available to outside organisations. Signed... 7. (candidate) D ate.. ......% 1 . /o s J q % Contents Abstract jj Acknowledgements iv Author's declaration vi Contents vii List of tables xiii List of figures xiv Abbreviations xvii CHAPTER 1 - GENERAL INTRODUCTION 1 1.1. Slugs as pests 1 1.1.1. Damage to crops and yield losses 2 1.1.2. Changing agriculture and the effects on slug populations 2 1.1.3. Why is Deroceras reticulatum such an important slug pest? 2 1.1.4. Biology and ecology of Deroceras reticulatum and Arion intermedius 3 1.2. Methods of controlling slugs 4 1.2.1. Chemical control 5 1.2.2. Cultural control 6 1.2.2.1. Intercropping 6 1.2.2.2. Seedbed condition 7 1.2.2.3. Tillage 7 1.2.2.4. Seed depth 7 1.2.2.5. Crop resistance 8 1.2.2.6. Sowing date 8 1.2.3. Biological control 8 1.2.3.1. Microsporidium novocastriensis 9 1.2.3.2. Tetrahymena rostrata 9 1.2.3.3. Phasmarhabditis hermaphrodita 9 1.2.3.4. Natural predators 10 1.2.3.5. Generalists as biological control agents 11 1.3. Ecology and Biology of Pterostichus melanarius 13 vii 1.4. Carabid beetles and slugs 13 1.4.1.