Principal Sunflower Bees of North America with Emphasis on the Southwestern United States (Hymenoptera: Apoidea) PAUL D. HURD, JR., WALLACE E. LaBERGE, and E. GORTON LINSLEY SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 310 SERIES PUBLICATIONS OF THE SMITHSONIAN INSTITUTION Emphasis upon publication as a means of "diffusing knowledge" was expressed by the first Secretary of the Smithsonian. In his formal plan for the Institution, Joseph Henry outlined a program that included the following statement: "It is proposed to publish a series of reports, giving an account of the new discoveries in science, and of the changes made from year to year in all branches of knowledge." 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Papers or monographs submitted for series publication are received by the Smithsonian Institution Press, subject to its own review for format and style, only through departments of the various Smithsonian museums or bureaux, where the manuscripts are given substantive review. Press requirements for manuscript and art preparation are outlined on the inside back cover. S. Dillon Ripley Secretary Smithsonian Institution SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 310 Principal Sunflower Bees of North America with Emphasis on the Southwestern United States (Hymenoptera: Apoidea) Paul D. Hurdjr., Wallace E. LaBerge, and E. Gorton Linsley SMITHSONIAN INSTITUTION PRESS City of Washington 1980 ABSTRACT Hurd, Paul D., Jr., Wallace E. LaBerge, and E. Gorton Linsley. Principal Sunflower Bees of North America with Emphasis on the Southwestern United States (Hymenoptera: Apoidea). Smithsonian Contributions to Zoology, number 310, 158 pages, 1 frontispiece, 11 figures, 5 plates, 17 tables, 1980.—This investigation focuses primarily on those ecological and evolutionary aspects involved in the natural history of the bees that utilize the pollen, nectar, or both, of sunflowers (Helianthus) in North America either for their survival as species or for their maintenance in viable populations. This bee-flower asso- ciation is examined principally by analyses of the intrafloral, geographic, diurnal, and seasonal interrelationships that exist between this fauna of bees and the various species of Helianthus present in North America. On the basis of this study it is established that more than 400 species of native bees visit the flowers of Helianthus in America north of Mexico. Of these it is those species that have evolved a specialized intrafloral relationship with these flowers that serve as the principal pollinators of these plants. OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: The coral Montastrea cavemosa (Linnaeus). Library of Congress Cataloging in Publication Data Hurd, Paul David, 1921- Principal sunflower bees of North America with emphasis on the Southwestern United States (Hymenoptera, Apoidea) (Smithsonian contributions to zoology ; no. 310) Bibliography: p. 1 Bees—Southwest, New. 2. Bees—North America. 3. Helianthus. 4. Insect-plant relation- ships. 5. Insects—Southwest, New. 6. Insects—North America., I. LaBerge, Wallace E joint author. II. Linsley, E. Gorton, joint author. III. Title. IV. Series: Smithsonian Institution. Smithsonian contributions to zoology ; no. 310 QL1.S54 no.310 [QL567.1 .S68] 591'.08s [b9b.TWM19] 79-18794 Contents Page Introduction 1 Methods of Study 2 Sampling Procedures 3 Acknowledgments 3 Principal Sampling and Survey Sites 5 Chihuahuan Desert 6 Sonoran Desert 8 Mojave Desert 9 Cismontane California 9 Primary Host Plant 11 Intrafloral Relationships of Bees Associated with Helianthus 17 Oligoleges of Compositae Primarily Associated with Helianthus 24 Oligoleges of Compositae Secondarily Associated with Helianthus ... 24 Regular Polyleges Associated with Helianthus 25 Casual Polyleges Associated with Helianthus 26 Nectar Visitors Not Known To Take Pollen from Helianthus 27 Parasitic Bees Known To Visit the Flowers of Helianthus 28 Species of Helianthus with Known Bee Visitors 28 Geographic Relationships of Bees Associated with Helianthus 31 Geographic Affinities of Helianthus Oligoleges and Polyleges 34 Seasonal Occurrence of Bees Associated with Helianthus 36 Diurnal Patterns of Pollen Collection 36 Species Accounts 36 Family COLLETIDAE 41 Family OXAEIDAE 43 Family ANDRENIDAE 43 Family HALICTIDAE 56 Family MELITTIDAE 69 Family MEGACHILIDAE 70 Family ANTHOPHORIDAE 89 Family APIDAE 119 Appendix: Tables 127 Literature Cited 143 Plates 154 in FRONTISPIECE.—Megachile parallela Smith (female) on flower of Helianthus. Principal Sunflower Bees of North America with Emphasis on the Southwestern United States (Hymenoptera: Apoidea) PaulD. Hurd Jr., Wallace E. LaBerge, and E. Gorton Linsley Introduction lateral and coevolution in insect-flower relation- ships. Perhaps the most characteristic and ne- The population aspects of bee-flower relation- glected of "all-day" plants in these regards are ships in the southwestern United States, espe- the sunflowers {Helianthus spp.), which provide a cially interspecific competition among pollen- continuously favorable environment for pollen- and nectar-seekers, have been studied for certain and nectar-seeking bees, both of which are capa- species in such diverse plant groups as the matinal ble of providing cross-pollination. flowering Camissonia, Cucurbita, Solatium, Cassia, Heiser et al. (1969), in the most recent mono- and Kallstroemia, the late afternoon flowering graph of North American sunflowers, state that Mentzelia, and the evening flowering Oenothera, with the exception of H. agrestis and a certain where competition is often intense during the cultivated strain of H. annuus, all species of He- short diurnal blooming period (Linsley, 1978). lianthus are self-incompatible and cross-pollina- Only recently have quantitative data become tion is obligate, and that no detailed study of available on pollen and nectar utilization among pollinators has been made other than for culti- flower visitors to plants that present nectar and vated forms of H. annuus (Free, 1964). These pollen throughout the day (e.g. Larrea, Hurd and authors remark, however, that from observations Linsley, 1975; Clarkia, MacSwain et al., 1973). in the field and in the experimental garden it is Clarification of the roles and competitive rela- obvious that the principal pollinators are bees, tionships of oligoleges, regular polyleges, and cas- including the introduced European honeybee. ual polyleges has provided new insights into uni- They note that butterflies visit sunflowers ex- tremely rarely, and that their occasional visits Paul D. Hurd, Jr., Department of Entomology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560. have usually been to the pale primrose form (or Wallace E. LaBerge, Section of Faunistic Surveys and Insect Identi- strain) of H. debilis ssp. cucumerifolius. fication, Illinois Natural History Survey, Urbana, III. 61801. E. Gorton Linsley, Department of Entomological Sciences, University of While it is technically true that no detailed California, Berkeley, Calif 94720. general study of Helianthus pollinators has been I SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY made (and this actually applies to the cultivated ico to the upper Mojave, the Colorado Desert, strains of H. annuus), several preliminary lists of and the San Joaquin Valley of California. Spe- sunflower visitors in various parts of the country cific objectives of this study were to determine the have been published (see "Intrafloral Relation- extent to which pollinators are specific to, or show ships of Bees Associated with Helianthus" herein). a marked preference for, Helianthus, and to quan- These, along with scattered data in entomological tify data on interspecific competition among pol- monographs and local lists, as well as preliminary linators. Cockerell (1914b) has correctly remarked samples taken by us in 1973 and 1974, indicated that male bees visiting sunflowers get covered that quantitative studies on diurnal and seasonal with pollen, and must be almost as useful as cycles and interspecific competition among bee females in the pollination of sunflowers. Thus we visitors would hold promise of yielding interesting have included records of floral visits of male bees ecological and evolutionary data. and nectar-seeking females as well as females that Reports concerning bees visiting particular spe- gather pollen. cies of Compositae in the southwestern United Unfortunately, the manuscript was completed States are very few.