Diptera: Ceratopogonidae)

Ecological studies on Cuilcoides impunctatus (Diptera: Ceratopogonidae) with reference to its control in the Highlands of Scotland Peter Michael Marsh Thesis presented for the degree of Doctor of Philosophy University of Edinburgh 1986 Abstract Biting midges (Cuilcoides spp. - Diptera: Ceratopogonidae) were studied by Loch Awe in Argyllshire, Scotland. In this holiday area, Cu//co/des impunctatu. the 'Highland midge', presents a real threat to tourism. Most of the conclusions relate to this species. The diel flight periodicity of Cu//co/des impunctatus was found to be dependent on trapping technique and location of capture. Using suction-trap catches, typical crepuscular activity was observed in a forest. The 'rest phase' during the daytime was considered to be dictated by circadian rhythms. A similarly-positioned human bait, however, not only recorded dusk and dawn peaks, but also indicated that a potential blood-source could induce daytime attack activity in previously resting adults. By contrast, simultaneous flight-periodicity determinations by both a human bait and a suction trap in a nearby exposed field were similar in form to that observed using a suction trap in the forest. The less favourable environmental conditions and the paucity of resting sites in the field were considered to explain the discrepancy between the two human-bait catches. An attempt was made to model the flight activity of Cuilcoides /mpunctatus using a 'least squares' regression analysis. The necessity to allow for the possible effect of circadian rhythms was emphasized. The model, in consequence, not only incorporated elements to describe (theoretically) the influence of both the more conspicuous weather factors and any change in the population density, but also analysed the relationship to 'time of day'; an indirect way of modelling rhythmically-determined activity. Furthermore, data taken from within the putative rest phase of the diel activity cycle were omitted. Although the results seemed plausible - for instance, flight activity was found to be negatively correlated with wind speed and strongly related to time of day - little confidence was placed in the parameter estimates. Regression techniques, it was concluded, are ill-suited to describe the complexities of flight activity. Entomologists were strongly urged to recognise the limitations of statistics and to interpret their data accordingly. A time-dependent Poisson process was used to investigate whether midges (almost exclusively Cuilcoides impunctatus and C. obsoletus grp) attack a human in a random manner. The results indicated that the landing distribution was clumped with respect to time. The adaptive significance of this behaviour is difficult to explain. The problem that midges pose to the tourist industry of the Highlands and Islands was considered at length in relation to insect control methods currently in use worldwide. Although the situation for the paying tourist could be improved, the actual elimination of the pest species, it was felt, would be neither economically sound nor environmentally desirable. Ultimately it was concluded that the severity of a particular highland area's midge problem is very subjective, strongly determined by sociological considerations. Declaration This thesis has been composed by myself, and the work described in it is My own unless explicitly acknowledged. List of contents Acknowledgments 1. General introduction 1.1. Conception of the study 1.2. The genus Cu//co/des: a brief introduction 2 1.3. Life history of Cuilcoides impunctatus 4 1.3.1. Egg stage 4 1.3.2. Larval stage 5 1.3.3. Pupal stage 6 1.3.4. Adult stage 6 1.4. Aspects of Cuilco/des ecology and control investigated 10 2. Materials and methods 2.1. The study area 12 2.2. Environmental monitoring system 15 2.2.1. Data logging 15 2.2.2. Air temperature 17 2.2.3. Relative humidity 17 2.2.4. Wind: speed and direction 17 2.2.5. Light 18 2.3. Suction traps 19 2.4. Human-bait catches 22 2.5. Preserving and sorting 24 2.6. Sub-sampling and identification 25 3. Flight periodicity in relation to microclimate and method of capture 3.1. Introduction 27 3.2. Control of flight periodicity 28 3.3. How are rhythms adaptive? 33 3.4. Methods 34 3.4.1. Experimental sites 34 The Field Site 34 The Forest Site 37 3.4.2. Experimental design 38 3.5. Expressing flight periodicity: measures of central tendency 39 3.6. Results 40 3.6.1. Environmental conditions 40 Air temperatures 43 Relative humidities 43 Wind speeds 46 Light levels 46 3.6.2. Flight periodicities of Cuilcoides impunctatus 49 Forest Site - suction trap 49 Forest Site - human bait 49 Field Site - suction trap 49 Field Site - human bait 52 3.6.3. The 'daylight hours' catches: a statistical comparison 52 3.6.4. Flight periodicities of other species 55 3.7. Discussion 55 3.7.1. Why do flight activity patterns vary with trapping 57 technique and location of capture? 3.7.2. Why is crepuscularity fairly typical of the genus? .60 3.7.3. Are the individuals caught during periods of low activity 62 physiologically distinct from those taken at times of peak flight? 4. 'Modelling' flight activity of Cu//co/des impunctatus 4.1. Introduction 65 4.2. Is a regression analysis applicable to the problem? 68 4.3. Factors governing the size of suction-trap catches 71 4.3.1. The trap constant 72 4.3.2. The adult population density 72 4.3.3. Rhythms 74 4.3.4. Environmental variables and factors 74 a) Air temperature 75 b) Relative humidity 81 c) Wind speed 86 d) Light 91 e) Rain 96 f) Wind direction 97 4.4. Selecting the data for the analysis 97 4.4.1. Source of the data 97 4.4.2. The 'daylight hours' catches: their exclusion 98 4.4.3. Thresholds 99 4.5. Transforming the response variable 100 4.6. The statistical model 101 4.7. Results 102 4.8. Discussion 104 4.8.1. TRIAL 105 4.8.2. TIME 105 4.8.3. Temperature 106 4.8.4. Relative humidity 107 4.8.5. Wind speed 107 4.8.6. Light 108 4.8.7. RAIN and WIND DIRECTION 108 4.9. Conclusion log 5. Temporal attack patterns of Cuilcoides impunctatus and C. obso/etus grp 5.1. Introduction 111 5.2. Materials and methods 112 5.2.1. Experimental procedure 112 5.2.2. Statistical theory 114 5.3. Results 119 5.3.1. Landing distribution of Culicoidesspp. over periods of 119 one hour 5.3.2. Inter-arrival times 121 5.4. Discussion 124 6. Midges and the tourist industry of the Highlands and Islands 6.1. Introduction 128 6.2. Effect on the tourist 129 6.2.1. Physiological effects 129 6.2.2. Psychological effects 130 6.3. Effect on the tourist industry 131 6.4. History of midge control in Scotland 132 6.5. Pest species in Scotland 133 6.6. Duration of the problem 134 6.7. What level of control is necessary? 134 6.8. Flight range and its bearing on midge control 136 6.9. Chemical control 137 6.9.1. Adulticides 137 6.9.2. Larvicides 140 6.10. Biological control 142 6.10.1. Predators, parasites and pathogenic microbes 142 6.10.2. Competitors 144 6.10.3. Sterilization and genetic control 144 6.11. Environmental management 145 6.11.1. Environmental modification 146 a) Impounding breeding sites 147 b) Draining breeding sites 148 c) Land filling 149 6.11.2. Environmental manipulation 149 6.11.3. Modification or manipulation of human habitation or 150 behaviour a) Location of tourist area 150 b) Midge-proofing habitations 152 c) Personal protection 153 6.12. Conclusions 155 7. Concluding discussion 158 References Appendices Appendix 1. Flight activity patterns of female Cuilcoides impunctatus: Field Site and suction trap. Trials 1 to 8 Appendix 2. Multiple linear regression analysis: data Appendix 3. Artificial ventilation of a chalet balcony Figures Figure 2-1. The village of Dalavich by Loch Awe, Argyllshire 13 Figure 2-2. Map of the study area 14 Figure 2-3. The weather station in the Field Site showing, the 16 psychrometer unit, the windvane, the light sensor and the anemometer Figure 2-4. Cross-sectional view of a modified 'Wainhouse' (1980) suction trap Figure 2-5. The suction trap in the Forest Site 21 Figure 2-6. The human bait (P.M.M.) catching in the Forest Site 23 Figure 3-1. Map of the experimental site 35 Figure 3-2. The Field Site, showing the human bait, the 36 micrometeorological equipment and the suction trap Figure 3-3. Diel air temperature cycles in the Field and Forest Sites: 41 mean and range Figure 3-4. Diel humidity cycles in the Field and Forest Sites: 42 mean and range Figure 3-5. Diel wind speed cycles in the Field and Forest Sites: 44 mean and range Figure 3-6. Diel light cycles in the Field and Forest Sites: 45 mean and range Figure 3-7. Flight periodicity of female Cuilco/des impunctatus: 47 Forest Site and suction trap Figure 3-8. Flight periodicity of female Cu//co/des impunctatus: 48 Forest Site and human bait Figure 3-9. Flight periodicity of female Cuilco/des impunctatus: 50 Field Site and suction trap Figure 3-10. Flight periodicity of female Cuilco/des impunctatus: 51 Field Site and human bait Figure 3-11. Flight periodicity of female Cu//co/des obso/etusgrp: 53 Forest Site and suction trap Figure 3-12. Flight periodicity of female Cu//co/des obsoletusgrp: 54 Field Site and suction trap Figure 4-1. Scatter diagram: air temperature and number of insects 79 Figure 4-2.

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