University of Calgary PRISM: University of Calgary's Digital Repository Graduate Studies Legacy Theses 2001 The incidence of parasitism by conopid and phorid flies and its effects on the behavior of bumble bees(Hymenoptera: Apidae) Otterstatter, Michael C. Otterstatter, M. C. (2001). The incidence of parasitism by conopid and phorid flies and its effects on the behavior of bumble bees(Hymenoptera: Apidae) (Unpublished master's thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/18191 http://hdl.handle.net/1880/40970 master thesis University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission. 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Please contact the University of Calgary Archives for further information, E-mail: [email protected] Telephone: (403) 220-7271 Website: http://www.ucalgary.ca/archives/ UNIVERSITY OF CALGARY The Incidence of Parasitism by Conopid and Phorid Flies and its Effects on the Behaviour of Bumble Bees (Hymenoptera: Apidae) by Michael C. Otterstatter A THESIS SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE DEPARTMENT OF BIOLOGICAL SCIENCES CALGARY, ALBERTA JUNE, 2001 © Michael C. Otterstatter 2001 ABSTRACT Phorid and conopid flies parasitize bumble bees (Bombus spp.) in southwestern Alberta. Conopids parasitized bees at several sites, whereas phorids parasitized bumble bees extensively only at Barrier Lake. The prevalence of phorids and conopids differed among bumble-bee species and sexes. Although phorids and conopids may increase their reproductive success by parasitizing relatively large bees through more (phorid) or larger (conopids) offspring, large bees were rare at my study site. Nevertheless, conopids tended to parasitize large bees and thereby achieved heavier offspring. In contrast, phorids achieved relatively large offspring on small bees when few larvae developed per bee. The lifespan of bumble bees in the laboratory was reduced considerably by phorid parasitism, but less so by conopid parasitism, and similar results are expected among bees in the field. Conopid parasitism affected the incidence of pollen collection by bees, but neither phorid nor conopid parasitism affected the species of pollen that bees collected. iii ACKOWLEDGEMENTS Many people helped me complete this thesis and I am very grateful for their contributions. My examining committee, Rob Longair, Gordon Pritchard and Ralph Cartar provided thoughtful comments on this thesis. The students of Lawrence Harder's lab, Crispin Jordan, Eric Gross, Taline Sarkissian, Jannice Friedman and Chris Borkent made my M.Sc. experience an enjoyable one. Crispin Jordan provided many interesting and humorous discussions and jamming time for which I am very grateful. Corey Corbett helped me considerably with collecting and processing bumble bees. Judy Buchanan-Mappin provided me with weather data from the University of Calgary field station in Kananaskis. Brian Brown identified my phorid flies and helped with ideas and discussions pertaining to phorid parasitism of bumble bees. Troy Whidden helped with interesting discussions and introduced me to bumble-bee collecting and rearing. Lawrence Harder and Robin Owen were especially helpful throughout my M.Sc. Lawrence went far beyond his obligations as co-supervisor and provided help with every aspect of this thesis. His guidance and support help me enormously and I am extremely grateful. Robin turned me on to how interesting and enjoyable bumble bees can be to work with and encouraged me to pursue graduate studies. He provided me with encouragement and financial support and was an excellent supervisor. Nora Saona was especially supportive and provided encouragement, warmth, food and all the things necessary to make me happy. TABLE OF CONTENTS PAGE APPROVAL PAGE ii ABSTRACT iii ACKNOWLEDGEMENTS iv TABLE OF CONTENTS v LIST OF TABLES viii LIST OF FIGURES x 1 Introduction 1 1.1 Parasitoids of social insects 1 1.2 Parasitoids of bumble bees (Hymenoptera: Apidae) 3 1.3 Objectives 10 2 General methods 12 2.1 Study site 12 2.2 Collecting bumble bees 12 3 Ecology and distribution of diptera parasitoids of bumble bees in SW Alberta 15 3.1 Introduction 15 3.2 Methods 18 3.2.1 Study sites 18 3.2.2 Statistical analyses 19 3.3 Natural history 19 3.3.1 Apocephalus borealis 19 v 3.3.2 Conopid parasitoids of bumble bees 21 3.4 Results 23 3.4.1 Phorid parasitism of bumble bees in southwestern Alberta 28 3.4.2 Conopid parasitism of bumble bees in southwestern Alberta 28 3.5 Discussion 28 4 Host selection by phorid and conopid parasitoids of bumble bees 33 4.1 Introduction 33 4.2 Methods 35 4.2.1 Capture of adult parasitoids 35 4.2.2 Statistical analyses 36 4.3 Results 39 4.3.1 Phorid parasitism of bumble bees 42 4.3.2 Conopid Parasitism of Bumble Bees 68 4.4 Discussion 79 4.4.1 Phorid parasitism of bumble bees 79 4.4.2 Conopid parasitism of bumble bees 87 4.4.3 Host use by phorid and conopid parasitoids of bumble bees 90 5 Effects of dipteran parasitism on bumble-bee survival and behaviour 91 5.1 Introduction 91 5.2 Methods 93 5.2.1 Collecting methods 93 5.2.2 Pollen load analysis 93 vi 5.2.1 Collecting methods 93 5.2.2 Pollen load analysis 93 5.2.3 Statistical analyses 94 5.3 Results 96 5.3.1 Effects of parasitism on bumble-bee survival 96 5.3.2 Effects of parasitism on pollen collection by worker bumble bees... 102 5.4 Discussion 112 5.4.1 Effects of parasitism on bumble-bee survival 112 5.4.2 Effects of parasitism on pollen collection by worker bumble bees... 117 6 Conclusions 121 7 Literature Cited 124 vii LIST OF TABLES TABLE TITLE PAGE 1.1 Dipteran and hymenopteran parasitoids of bumble bees 4 3.1 Parasitism of bumble bees by phorid and conopid flies in SW Alberta 24 4.1 Statistics describing the effects of bumble-bee species, sex and year on the probabilities of phorid and conopid parasitism 45 4.2 ANOVA results for comparison of bumble-bee mass between phorid parasitized and unparasitized bees during 1999 and 2000 46 4.3 Capture of adult A. borealis by sticky traps on different plant species 55 4.4 Analysis of phorid clutch size, pupal mass, larval survivorship and brood sex ratio during 1999 and 2000 56 4.5 Characteristics of phorid clutches on different bumble-bee species 60 4.6 ANOVA results for comparison of bumble-bee mass between conopid parasitized and unparasitized bees during 1999 and 2000 71 4.7 Analysis of the survival of conopid larvae and conopid pupal mass 80 5.1 Statistics comparing the survival of parasitized and unparasitized bumble bees 99 5.2 Statistics describing the effects of residual lifespan, bumble-bee species, month and year on the proportion of unparasitized workers collecting pollen. 108 5.3 Statistics describing the effects of parasitism, residual lifespan, bumble-bee species and year on the proportion of workers collecting pollen 109 5.4 Simpson's Diversity Index for pollen loads from parasitized and unparasitized worker bumble bees 110 5.5 Proportion of pollen of the same species as the plant on which bees were collected for pollen loads from parasitized and unparasitized workers Ill ix LIST OF FIGURES FIGURE TITLE PAGE 3.1 Distribution of phorid and conopid parasitism of bumble bees in SW Alberta..27 4.1 Seasonal a) prevalence of phorid and conopid parasitoids in bumble bees, and b) abundance of bumble-bee species during 1999 and 2000 41 4.2 Incidence of phorid and conopid parasitism among a) bumble-bee species during 1999 and b) during 2000, and c) among bumble-bee sexes 44 4.3 Mass of phorid parasitized and unparasitized bumble bees 48 4.4 Incidence of phorid parasitism among pollen- and nectar-collecting workers. .50 4.5 Incidence of phorid parasitism among bumble bees collected on different plants for a) all bee species pooled, and b) two representative bee species.. ..53 4.6 Relation of phorid clutch size to host mass during 1999 and 2000 58 4.7 Relation of total mass of phorid pupae per bee to a) clutch size during 1999 and b) during 2000, and c) to host mass during 1999 and d) during 2000...62 4.8 Relation of mean mass of phorid pupae per bee to host mass 65 4.9 Relation of mean proportion of phorid larvae per bee that survived to pupation to clutch size during 1999 and 2000 67 4.10 Mass of conopid parasitized and unparasitized bumble bees 73 4.11 a) Relation of conopid pupal mass to host