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STRUCTURAL, BEHAVIORAL, AND PHYSIOLOGICAL ADAPTATIONS OF BEES (APOIDEA) FOR COLLECTING POLLEN1 ROBBIN W. THORP2 ABSTRACT Bees, like their wasp relatives, forage for and transport food to a nest as provisions for theiroffspring. Unlike female Sphecoidea which transport arthropods one at a time as prey, bees transportpollen requiring specialized scopal (brush) or corbicular (fringed plate) structures to transport thedustlike material externally. Scopae often exhibit further modifications in density and amount ofplumosity in relation to the size and ornamentation of the pollen grains they transport. Bees alsodiffer from sphecid wasps by possessing branched body hairs that are relatively densely packed.These hairs, the electrostatic surface potential, and specialized hair groups for extraction of hiddenpollen are important in the acquisition of pollen from flowers. Structures for grooming (brushes,combs, and scrapers) and grooming behavior patterns are modified to permit manipulation and packingof pollen in the specialized transport structures. The addition of nectar, so that pollen is packed moist,is a behavior that permits the carrying of pollen of a great variety of sizes and ornamentations inrelatively simplified scopae or in corbiculae. The addition of oils to the diet of some bees has resultedin a modified type of scopal structure that has a wooly area basally and stiff guard hairs extendingdistally and that can transport a mixture of oil and pollen. Special hairs on the fore and mid basitarsiand teeth of hind tibial spurs are modified as oil scraper and manipulation structures. The use ofcorbiculae in Apidae to transport nesting materials and the hind tibiae in male orchid bees (Euglossini:Apidae) for transporting aromatic compounds involves behavior patterns similar to those for pollentransport in grooming, manipulating, and packing the materials. Other behavioral and physiologicaladaptations important in the location and acquisition of pollen by bees include individual constancy,oligolecty, seasonal synchrony, preimaginal conditioning, daily synchrony, buzz pollination, and otherresponses to specific modes of pollen presentation. Most of the behavioral patterns involve learning.They may be modified by extrinsic factors, and they may modify intrinsic structural and physiologicalcharacters. Bees share a common ancestry with sphecoid wasps, but feed on plant ma-terials rather than arthropod prey. Like their wasp relatives, female bees foragefrom a nest to which they must transport food for their offspring. Sphecoid waspscommonly transport single arthropods held in the mandibles often assisted by thelegs, but some advanced sphecids transport their prey in a more rearward positionsupported primarily by the mid legs or occasionally by special modifications ofthe sting or pygidial plate (Evans, 1962). Since pollen, the principal brood foodof Apoidea, occurs primarily as a fine-grained (5-210 �m), dustlike material, mostbees have evolved highly specialized adaptations for pollen transport. Most beescarry some pollen mixed with nectar in the crop or honey stomach. Few beestransport pollen exclusively in the crop as do honey wasps (Pseudomasaris: Ma-saridae) (Torchio, 1970). However, females of a1l other nonparasitic bees trans-port pollen externally in specialized structures called scopae (brushes of hairs) 'Supported in part by University of California, Davis Faculty Research Grant D-798 and a USDACooperative Agreement. I am greatful to Elizabeth Toftner, Karen Luchessa, Rick Harris, and PaulKnoll for assistance with the scanning electron micrography, and Dennis Briggs for the macropho-tography and preparation of ail photos used. Special thanks are due to Dr. J. J. Pasteels for the loanof the manuscript in press on halictine scopae, and to Drs. E. G. Linsley and C. D. Michener foruseful comments on this paper. 2 Department of Entomology, University of California, Davis, California 95615.ANN. MISSOURI BOT. GARD. 66: 788-812. 1979. 0026-6493/79/0788-0812/$02.65/0



Structural, Behavioral, and Physiological Adaptations of Bees (Apoidea) for Collecting Pollen

Robbin W Thorp
Annals of the Missouri Botanical Garden 66: 788-812 (1979)

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