The Principal Larrea Bees of the Southwestern United States (Hymenoptera: Apoidea) PAUL D. HURD, JR. and E. GORTON LINSLEY SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 193 SERIAL PUBLICATIONS OF THE SMITHSONIAN INSTITUTION The emphasis upon publications as a means of diffusing knowledge was expressed by the first Secretary of the Smithsonian Institution. In his formal plan for the Insti- tution, Joseph Henry articulated 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." This keynote of basic research has been adhered to over the years in the issuance of thousands of titles in serial publications under the Smithsonian imprint, com- mencing with Smithsonian Contributions to Knowledge in 1848 and continuing with the following active series: Smithsonian Annals of Flight Smithsonian Contributions to Anthropology Smithsonian Contributions to Astrophysics Smithsonian Contributions to Botany Smithsonian Contributions to the Earth Sciences Smithsonian Contributions to Paleobiology Smithsonian Contributions to Zoology Smithsonian Studies in History and Technology In these series, the Institution publishes original articles and monographs dealing with the research and collections of its several museums and offices and of professional colleagues at other institutions of learning. These papers report newly acquired facts, synoptic interpretations of data, or original theory in specialized fields. These pub- lications are distributed by mailing lists to libraries, laboratories, and other interested institutions and specialists throughout the world. Individual copies may be obtained from the Smithsonian Institution Press as long as stocks are available. S. DILLON RIPLEY Secretary Smithsonian Institution SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 193 The Principal Larrea Bees of the Southwestern United States (Hymenoptera: Apoidea) Paul D. Hurd, Jr. and E. Gorton Linsley SMITHSONIAN INSTITUTION PRESS City of Washington 1975 ABSTRACT Hurd, Paul D., Jr., and E. Gorton Linsley. The Principal Larrea Bees of the Southwestern United States (Hymenoptera: Apoidea). Smithsonian Contributions to Zoology, number 193, 74 pages, 18 figures, 15 tables, 1975.—This investiga- tion focuses primarily on those ecological and evolutionary aspects involved in the natural history of the bees which depend upon the pollen, nectar, or both of the creosote bush (Larrea tridentata) in North America for their survival either as species or for their maintenance in viable populations. This bee-plant (bee- flower) association is examined principally by analyses of the intrafloral, geo- graphic, diurnal, and seasonal interrelationships that exist between this fauna of bees and the plant. OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SI PRESS NUMBER 5253. SERIES COVER DESICN: The coral Montastrea cavernosa (Linnaeus). Library of Congress Cataloging in Publication Data Hurd, Paul David, 1921- The principal Larrea bees of the southwestern United States (Hymenoptera, Apoidea) (Smithsonian contributions to zoology, no. 193) Supt. of Docs, no.: SI 1.27:193 1. Bees—Southwest. 2. Insect-plant relationships. 3. Cresote bush. I. Linsley, Earle Gorton, 1910- joint author. II. Title. III. Series: Smithsonian Institution. Smithsonian contributions to zoology, no. 193. QL1.S54 no. 193 [QL568.A6] 591'.08s [595.7'9] 74-22289 Contents Page Introduction 1 Methods of Study 3 Sampling Methods 4 Principal Sampling and Survey Sites 5 Upper Rio Grande Valley, New Mexico 6 Western New Mexico 6 San Simon Valley and Vicinity, Arizona and New Mexico 6 Southeastern Arizona 7 San Pedro River Valley, Arizona 7 Tucson Basin, Arizona 7 Colorado River Valley, Arizona and California 8 Colorado Desert, California 8 Intrafloral Relationships of Bees Associated with Larrea in the South- western United States 8 Geographic Relationships of Bees Associated with Larrea in the South- western United States 10 Geographic Affinities of Southwestern Larrea Oligoleges and Regular Polyleges 13 Seasonal Occurrence of Bees Associated with Larrea in the Southwestern United States 13 Diurnal Patterns of Pollen Collection 15 Species Accounts 16 Family Colletidae 18 Family Andrenidae 22 Family Oxaeidae 27 Family Halictidae 27 Family Melittidae 32 Family Megachilidae 33 Family Anthophoridae 39 Family Apidae 48 Appendix: Tables 49 Literature Cited 70 The Principal Larrea Bees of the Southwestern United States (Hymenoptera: Apoidea) Paul D. Hurd, Jr. and E. Gorton Linsley Introduction Chihuahuan desert regions of North America and to analogous desert regions centering around north Botanists, since the writings of Gray and Hooker Chile and northern Argentina in South America. (1880) and Engler (1882), have been intrigued by Thus, he points out, closely similar species of certain similarities in the temperate floras of North Larrea and at least three different sections of and South America, particularly those elements Prosopis are prominent in arid zones of both common to the arid zones of the southwestern continents, Larrea tridentata occurring throughout United States and northern Mexico and counter- the Sonoran and Chihuahuan deserts and in iso- part areas in Argentina and Chile (e.g., Bray, 1898, lated localities south to Hidalgo, and its close 1900; I. M. Johnston, 1940; M. C. Johnston, 1962). relative, L. divaricata, in the deserts of Peru, Bo- Prominent among these elements are members of livia, Chile, and Argentina. He states that the the genus Larrea. There has been lack of agreement North American species is self-compatible and sets among botanists as to the appropriate name for the seed in isolation, citing as evidence a single shrub species of Larrea inhabiting North America, some in the San Joaquin Valley reported by Twissel- regarding it as conspecific with the South American mann (1956). This interpretation is consistent with Larrea divaricata, others as a distinct species, L. Raven's conclusion that nearly all of the plants tridentata. We follow Porter (1963, 1974) and with disjunct amphitropical distributions are self- Raven (1963) in utilizing the designation Larrea compatible. tridentata (creosote bush). When considering amphitropical distributions of Raven (1963), in his instructive discussion of plants, the question as to how and when the dis- amphitropical relationships in the floras of North junctions were formed is critical. Raven discusses and South America, recognizes three groups of several lines of evidence that can be utilized in plants with disjunct distributions: (1) the bipolar" discriminating among the various possible alterna- or high-latitude, (2) the temperate, and (3) the tives. One such source is the faunas associated with desert groups. The desert disjuncts consist of spe- the disjunct plants. He emphasizes that insects, cies or species groups confined to the Sonoran and which are predominantly bisexual, are often closely tied to a particular environment and are dispersed Paul D. Hurd, Jr., Department of Entomology, National with relative ease. Thus, if the amphitropical pal Museum of Natural History, Smithsonian Institution, Wash- terns of distribution are the result of relatively ington, D.C. 20560. E. Gorton Linsley, Department of En- tomological Sciences, University of California, Berkeley, recent migration, large numbers of common groups California 94720. of insects may be expected in the corresponding 1 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY regions of temperate North and South America. On thidiini and Megachilini. To provide a broad base the other hand, if the plant distributions are the of phylogenetic contrast, species of the families result of long-distance dispersal, very few common Colletidae, Andrenidae, Anthophoridae, Mega- genera and species of insects would be expected. chilidae, Melittidae, and Oxaeidae were selected When considering the distributions of phyto- for special studies of their intrafloral relationships phagous insects associated with disjunct amphi- with Larrea. Information derived from these sources tropical plants, the principal questions are (1) to is expected to assist in distinguishing between con- what extent do the insects associated with the vergent evolution of adaptations and adaptations disjunct plants represent similarly disjunct species derived from a common ancestor. or groups of closely related species, (2) to what 2. Characterization of the results of convergent extent do those counterpart insects which were and divergent evolution, including adaptive radia- derived from related but distinct evolutionary lines tion, in selected genera of bees with known amphi- exhibit similar means of exploiting the counter- tropical distributions in the Americas. This has part host plants, and (3) to what extent have more entailed investigations of morphology, pollen rela- distantly related phytophagous insects developed tionships, behavior, and seasonal responses of bees similar methods for exploiting these same plants. to pollen and nectar availability. Phylogenetic studies of bees on a world basis 3. Identification of the factors underlying popu- indicate that the amphitropical bee faunas of the lation variation and the processes responsible for Americas have evolved basically from independent promoting convergent and divergent evolution. stocks. All presently available evidence