Amblyseius Swirskii (Athias-Henriot) (Acari:Phytoseiidae) and Phytoseiulus Longipes (Evans) (Acari:Phytoseiidae)
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Thermal biology and behaviour of two predatory Phytoseiid mites: Amblyseius swirskii (Athias-Henriot) (Acari:Phytoseiidae) and Phytoseiulus longipes (Evans) (Acari:Phytoseiidae) by Claire Marie Allen A thesis submitted to The University of Birmingham for the degree of DOCTOR OF PHILOSOPHY School of Biosciences The University of Birmingham September 2009 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. ABSTRACT Amblyseius swirskii and Phytoseiulus longipes are targeted as biological control agents for the horticultural pest Tetranychus urticae. This study applies a standardised protocol to evaluate the risk of establishment of introduced species and investigates temperature related behavioural thresholds for all three species. Laboratory results demonstrate a low level of cold tolerance in A. swirskii and no diapause. Field studies recorded 100% mortality within two weeks of outdoor winter exposure. Amblyseius swirskii has a higher activity threshold temperature than it’s target prey T. urticae. Amblyseius swirskii lacks cold tolerance and is unlikely to establish outdoors and thus can be considered a ‘safe candidate’ for release. Laboratory results demonstrate that P. longipes can not diapause yet is more cold tolerant than A. swirskii. Field studies report 100% mortality after 73 days of winter exposure. Phytoseiulus longipes demonstrates mid-range cold tolerance yet is unlikely to survive an entire winter outdoors. Phytoseiulus longipes has lower activity threshold temperatures than T. urticae. Further studies are required on other factors attributable to establishment potential before it can be classified a ‘safe candidate’. As a consequence of the findings of the present study A. swirskii was granted a license for release into the UK in 2006. TABLE OF CONTENTS Page CHAPTER 1: INTRODUCTION 1 1.1 Biological control 1 1.2 Glasshouse agriculture 5 1.3 Environmental concerns 6 1.4 Regulation and legislation 10 1.5 Insects at low temperatures 16 1.5.1 Developmental threshold 17 1.5.2 Thermal budget 19 1.5.3 Voltinism 19 1.5.4 Field survival 19 1.6 Insect Cold hardiness 20 1.6.1 Supercooling point 20 1.6.2 Lower lethal temperature 21 1.6.3 Lower lethal time 22 1.6.4 Freeze tolerance 24 1.6.5 Freeze avoidance 24 1.7 Diapause 26 1.7.1 Induction of Diapause 26 1.7.2 Maintenance of the diapausing state 29 1.7.3 Diapause termination 30 1.8 Physiological behaviour at low temperatures 31 1.8.1 Cold Torpor 31 1.8.2 Chill coma recovery 32 1.8.3 Motility and ability to predate 32 1.9 Phytoseiid mites 35 1.9.1 Amblyseius swirskii 36 1.9.2 Phytoseiulus longipes 39 1.10 Aims of study 41 CHAPTER 2: GENERAL METHODS 43 2.1 Introduction 43 2.2 Culturing mite populations 43 2.2.1 Tetranychus urticae culture 43 2.2.2 Amblyseius swirskii culture 44 2.2.3 Phytoseiulus longipes culture 46 2.3 Studying individual mites 48 CHAPTER 3: THERMAL BIOLOGY OF AMBLYSEIUS SWIRSKII 50 3.1 Introduction 50 3.2 Aims 51 3.3 Methods 52 3.3.1 Developmental time 52 3.3.2 Diapause 54 3.3.3 Supercooling points 54 3.3.4 Lower lethal temperatures 55 3.3.5 Lower lethal times 56 3.3.6 Field exposures 58 3.4 Results 60 3.4.1 Developmental time 60 3.4.2 Diapause 66 3.4.3 Supercooling points 67 3.4.4 Lower lethal temperatures 68 3.4.5 Lower lethal times 69 3.4.6 Field exposures 72 3.5 Discussion 78 CHAPTER 4 : LOW TEMPERATURE ACTIVITY THRESHOLDS OF AMBLYSEIUS SWIRSKII 89 4.1 Introduction 89 4.2 Aims 92 4.3 Methods 93 4.3.1 CTmin and chill coma 95 4.3.2 Chill coma recovery and activity recovery 96 4.3.3 Walking speed 96 4.3.4 Predation 97 4.4 Results 98 4.4.1 CTmin and chill coma 98 4.4.2 Chill coma recovery and activity recovery 100 4.4.3 Walking speed 102 4.4.4 Predation 104 4.5 Discussion 106 CHAPTER 5: THERMAL BIOLOGY OF PHYTOSEIULUS LONGIPES 113 5.1 Introduction 113 5.2 Aims 114 5.3 Methods 114 5.3.1 Developmental time 115 5.3.2 Diapause 116 5.3.3 SCP 116 5.3.4 Lower lethal temperatures 117 5.3.5 Lower lethal time 118 5.3.6 Field exposures 118 5.4 Results 121 5.4.1 Developmental time 121 5.4.2 Diapause 126 5.4.3 SCP 127 5.4.4 Lower lethal temperatures 128 5.4.5 Lower lethal time 129 5.4.6 Field exposures 132 5.5 Discussion 139 CHAPTER 6: LOW TEMPERATURE ACTIVITY THRESHOLDS OF PHYTOSEIULUS LONGIPES 150 6.1 Introduction 150 6.2 Aims 151 6.3 Methods 151 6.3.1 CTmin and chill coma 152 6.3.2 Chill coma recovery and activity recovery 153 6.3.3 Walking speed 153 6.3.4 Predation 154 6.4 Results 154 6.4.1 CTmin and chill coma 154 6.4.2 Chill coma recovery and activity recovery 156 6.4.3 Walking speed 158 6.4.4 Predation 160 6.5 Discussion 162 CHAPTER 7: GENERAL DISCUSSION 170 7.1 Establishment potential of Amblyseius swirskii in the UK 173 7.2 Establishment potential of Phytoseiulus longipes in the UK 176 7.3 Comparative thermal thresholds of Amblyseius swirskii, Phytoseiulus longipes and Tetranychus urticae 180 REFERENCES 185 Ch 1: Introduction CHAPTER 1 Introduction 1.1 Biological control Biological control is the manipulation, by mankind, of naturally occurring predation or parasitism of one organism by another. It is the regulation of plant and animal numbers by natural enemies. The phenomenon has long been applied by man, and involves the management of natural enemies, and sometimes the introduction of non- native species, to control pests. Pests are defined as a species whose activities cause damage to man. The principle definition of biological control is the action of parasites, predators and pathogens to maintain another organism’s population density at a lower average than would occur in their absence (DeBach 1964). Biological control is a manifestation of the natural associations between different kinds of organisms. It is dynamic and subject to disturbances by other factors; environmental change and to the specific adaptations, properties and limitations of the organisms involved in each interaction (Van den Bosch 1973). In this way, biological control is a form of population management, whereby a pest organism may be eliminated from the local area or more often, its numbers are suppressed to a level that no longer poses a nuisance or economic damage. The first orchestrated biological control programmes were set up by Chinese and Yemenite farmers who encouraged native predatory ants to protect citrus and date trees from insect pests (Van den Bosch 1973). In 1888 the predaceous Vedalia beetle, 1 Ch 1: Introduction Rodolia cardinalis (Mulsant) (Coleoptera: Coccinellidae), was imported to California from Australia to control the Cottony-Cushion Scale insect, Icerya purchasi (Maskell) (Homoptera: Margarodidae), a destructive pest in citrus groves and fruit plantations (Waage & Greathead 1988). This is considered the first example of a scientific and institutionally-backed biological control programme. There are three types of biological control, described as: (i) Classical control, this is the control of alien species using small scale releases leading to permanent establishment of co-evolved natural enemies from the origin of the pest species; (ii) Augmentative (Inundative) control, involving a mass release of laboratory-reared populations (indigenous or non-native) to control open field or glasshouse pests and are designed not to persist; and (iii) Conservation control, is the sustainable use of indigenous biological control agents against indigenous or non-native pests (Van den Bosch 1982). Biological control can be used as a pest control strategy on its own, or it may be integrated with other farming methods such as cultivation of resistant plant cultivars (including GM crops), pheromone traps and the application of chemical pesticides. This multi-strategy approach to pest control is termed Integrated Pest Management (IPM) and is thought to be the most cost effective measure of pest control. The central concept of IPM is often expressed in terms of the economic threshold, the point at which the cost of management intervention is less than the damage that can be expected if the problem is left untreated. Therefore the goal of pest management is to avoid losses associated with a particular intensity of a biological process which in this case is herbivory (Lockwood 2000; Hui & Zhu 2006; Estay et al., 2009; Singh & 2 Ch 1: Introduction Vyas 2009). Ideally, in biological control, the agent would act in a density-dependent manner to suppress the target process as it proceeds towards the economic injury level (Coll et al., 2007). Biological control often involves the search for natural enemies in the native home of the pest species, where a regulatory pressure is applied to that pest. These enemies are then collected, reared and released in large numbers into the country or area where the pest outbreak is occurring (Samways 1981). An important point to remember is that for control to be successful, conservation of all natural enemies is essential; this includes indigenous and exotic species.