The Corbiculae of Bees

Original article The corbiculae of bees Charles D. Michener Snow Entomological Division, Natural History Museum, and Department of Entomology, The University of Kansas, Lawrence, KS 66045, USA (Received 6 July 1998; accepted 23 August 1998) Abstract - The word corbicula is ordinarily used for the ’pollen basket’ on the outer side of the hind tibia of worker honey bees and related forms. Unrelated bees have comparable but nonhomol- ogous structures, often on other parts of the body. Such structures are described on the hind femora and on the propodeum, as well as on the hind tibiae of two diverse groups of bees. © Inra/ DIB/AGIB/Elsevier, Paris bees / Apoidea / corbicula / pollen transport / anatomy 1. INTRODUCTION of pollen; it is probably easier to remove pollen from a corbicula than to remove an equal amount of pollen carried within a Most female bees have areas of fre- long, brush of hairs. The carried in the tib- dense hairs, the for pollen quently scopae, carrying ial corbiculae of the corbiculate Apidae, pollen from its floral sources to nests. A such as Apis, is moistened with nectar to scopa can be on the hind legs, on the under- form a firm mass or pellet on each hind tibia. side of the or even on the sides of metasoma, In all other corbiculae the pollen is carried the There are various and propodeum. types dry. densities of scopal hairs, presumably related to the characteristics of the pollen to be car- The case can be made for limiting the ried [10]. A common development is a space word corbicula to structures on the hind tibia surrounded by fringes of long scopal hairs. that carry moistened pollen, because this is Such a space has been called a corbicula the familiar usage of the word. So limited, it [10] and serves for transport of a large bulk is applicable only to the tribes Apini, * Correspondence and reprints E-mail: [email protected] Bombini, Euglossini and Meliponini. How- space between these two zones of long hairs. ever, the term corbicula is used in the present The femoral surface of the corbicula is typ- broad sense by some authors [3, 10] and in ically flattened, hairless, impunctate, often fact a synonymous generic name for smooth and shining, but sometimes gives Canephorula, which carries dry pollen in a rise to a few long hairs or some short hairs. tibial corbicula, is Corbicula. Clearly vari- Because the lower surface of the femur is ous corbiculae are not homologous, any often formed into a strong longitudinal ridge more than a sternal scopa is homologous to from which the inner corbicular fringe arises, a tibial scopa. the femoral corbicula is often on the lower outer surface of the femur, rather than on One system for describing parts of legs the lower surface in a strict sense. The assumes that the legs are pulled out later- femoral corbicula is closed basal ally at right angles to the long axis of the basally by femoral hairs and the hairs body. I here follow the more traditional sys- principally by of the which are and curved tem in which are considered to be in trochanter, long legs in their normal the hind distad. They are especially well developed resting positions, in femur directed back beside the body of the the genus Andrena (Andrenidae), Dipha- and in Oxaeinae bee. Thus the corbicula of Bombus is on the glossinae (Colletidae), where have been a outer, not the anterior, surface of the hind (Andrenidae), they given the flocculus or floccus tibia and the two tibial spurs would be outer special name, (figures 3 and and inner, not anterior and posterior. 4). Museum specimens that do not have large pollen loads often have pollen entan- 2. FEMORAL CORBICULAE gled in the corbicular fringes, but not occu- pying the corbiculae themselves. It is pos- The most widespread corbicular site is sible that the smooth, hairless or sparsely on the underside of the hind femur of many haired lower femoral surface evolved in members of the short-tongued bee families some other connection, and not as a pollen- Stenotritidae, Colletidae, Andrenidae and carrying area. Halictidae. While in these fam- widespread Sometimes the outer and inner corbicular ilies, the femoral corbicula is absent or little curl until their meet and hide or in the colletid subfamilies fringes tips developed close the corbicula. Such well-developed Hylaeinae and Euryglossinae, in the fringes are found, for example, in the Dipha- andrenid Panurginae and some subfamily glossinae and Oxaeinae. On the other hand small genera of Andreninae, and in the hal- in some groups, perhaps especially in those ictid subfamily Rophitinae as well as in par- Leioproctus (Colletinae) with a well-devel- asitic Halictinae. (The higher classification oped sternal scopa, the corbicular fringes used herein is based on [1] and [8], sum- are reduced, not different from marized in [5].) This femoral corbicula is being very those of long-tongued bees, which are not formed a) a zone of by long, frequently considered to have a femoral corbicula. plumose hairs that arise on the upper part are Leioproctus subgenera Hex- of the outer surface or even on the Examples upper antheda and surface of the femur and curl downward, Cephalocolletes. over the outer femoral surface (figures 1 In the halictid genus Lasioglossum, sub- and 3), and b) a band or row of long, some- genus Sphecodogastra, the fringes consist times straight hairs that arise on the inner of simple hairs and are largely reduced and surface, frequently on the lower inner sur- rather weak. However, the lowermost row of face, of the femur (figures 2 and 4). These hairs of the outer fringe is isolated by a bare are the outer and inner corbicular fringes, area and consists of long curved bristles. respectively. The femoral corbicula is the This appears to be an adaptation for the use of pollen of Onagraceae which is webbed described above. Bees having such femora together by viscin threads. include the Melittidae (a name here used in the sense to The short hairs found on hind femora of broad include the three related families in and most non- spheciform wasps (Sphecidae, Crabronidae) segregated [1]) bees are widely distributed and frequently parasitic long-tongued (Megachilidae, as well as the appressed. In some wasps (e.g. Crahro), Apidae), short-tongued groups however, the under surface of the hind femur Panurginae (Andrenidae) and Rophitinae (Halictidae). These forms do not much is flattened and shining, with or without carry short hairs, and the short simple hairs of the pollen on the femora, the tibial scopa being the structure. Such outer and inner surfaces are directed down- major pollen-carrying femoral structure, however, with ward. The same is true of parasitic bees that intergrades that of most Colletidae, Andrenidae and do not collect pollen (Nomadinae and Eri- crocidini in the Apidae, Sphecodes and its Halictidae, which (except for the forms men- relatives in the Halictidae), and of nonpara- tioned above) have well-developed femoral fringes and corbiculae and appear to carry sitic bees that carry pollen in the crop instead more on the femora than on the tibiae. of externally (Euryglossinae and Hylaeinae pollen The Stenotritidae carry more on the in the Colletidae). In such forms there is no pollen tibiae than the have indication of the outer and inner corbicular femora, yet moderately short femoral fringes. developed although fringes. Perhaps only because they are generally The long-tongued bees, however, are not more hairy insects, many bees have hind as uniform as the above comments suggest. femora that differ from those described in For example, in the Megachilidae, Lithurgus the paragraph above by having longer and has long, curved hairs on the outer femoral often more abundant hairs. The largely bare surface, some of them arising on the upper under surface of the hind femur is therefore surface, and many hairs on the inner sur- better set off from the hairy outer and inner face as well. Thus there is an approach to surfaces, the downward-directed hairs of fringes although they do not carry much which suggest the corbicular fringes pollen. The same statements apply to Cer- atina and Allodape in the apid subfamily only sparsely haired and serves as a corbic- Xylocopinae, but Xylocopa in the same sub- ula. In many species of Andrena there is in family has only short femoral hairs. In these addition a vertical fringe along the anterior forms, the more or less smooth and largely margin of the side of the propodeum. Thus hairless lower surface of the femur is as in a propodeal corbicula is formed, demarked bees with a femoral corbicula. The apid by dorsal, posterior and anterior fringes (fig- tribes Bombini and Euglossini, however, ure 13). completely lack femoral fringes and the lower femoral surface or much of it is punc- tate with short hairs, much like the other 4. TIBIAL CORBICULAE: surfaces. The tribes Apini and Meliponini THE CORBICULATE APIDAE have scattered short hairs and no sugges- tions of fringes or of a femoral corbicula. Thus the corbiculate Apidae differ distinctly By far the best known corbicula, and the from other Apinae. one widely known as the corbicula, is on the outer side of the hind tibia of the Apini, The absence of a femoral corbicula in Bombini, Euglossini and Meliponini (Api- Melittidae and bees supports long-tongued dae). These are the bees in what was called the conclusion [1] that the short- previous the apine clade in recent phylogenetic stud- Melittidae is ancestral to or tongued family ies [8]; this is not the line of Silveira the sister of the bees.

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