Materials and methods 621 Materials

We studied honeybees (Apis mellifera) and bumblebees (Bombus terrestris) as exemplary species. Apis mellifera workers have a body length of 12.1 ± 0.3 mm (n = 10, mounted specimens), and a mean proboscis length between 6.05 and 6.40 mm in the three most often cultured subspecies [27]. The European bumblebee B. terrestris was used as an example of a large bee species. Bumblebees vary greatly in size because workers can be much smaller than queens. Body length of the tested workers was 12.0 ± 0.8 mm (n = 10, mounted specimens), but queens can reach a body length of 19 mm or more. Compared with other European bumblebee species, B. terrestris has a rather short proboscis of 8 to 9 mm length [28]. The bumblebee colonies were bought from a commercial supplier (Re-natur GmbH, D-24601 Ruhwinkel, Germany). Forces of bumblebees were measured in the laboratory, and forces of A. mellifera were measured in a private bee yard near Freiburg, Germany.

Flowers of the following Salvia species were studied: S. amplexicaulis Lam., S. forskahlii L., S. glutinosa L., S. cf. microphylla Kunth, S. nilotica Juss. ex Jacq., S. nubicola Wall. ex Sweet, S. phlomoides Asso, S. pratensis L., S. sclarea L., S. transsylvanica (Schur ex Griseb.) Schur, S. uliginosa Benth., S. verbenaca L., and S. viridis L. We took the flowers from plants that were cultivated in the Freiburg Botanical Garden (Southwestern Germany). Before flowers were analyzed mechanically, internal structure and morphology of each species was studied in a number of longitudinal sections and cross sections. The species we were especially interested in are:

Jupiter's distaff, S. glutinosa L., is a yellow-flowered species that occurs in European and Asian mountain forests. S. glutinosa has a simple lever morphology in the sense of Himmelbaur and Stibal [29]. The connective is strongly curved, and the flower entrance is not completely blocked by the lever (Figure 6.2A and Figure 6.7A). Flower-visiting insects on S. glutinosa were studied during the flowering periods in 2002 to 2004 in the Freiburg Botanical Garden and in 2003 to 2004 on a further site near Eichstetten (southwestern Germany) where this species grows naturally. Flowers are usually visited by bumblebees (see Table 6.1) and not by honeybees or other midsized bees except for some pollen-thieving or nectar-robbing visits.

Clary sage, S. sclarea L., is a well-known, light blue or pink to white flowering Mediterranean species that is widely cultivated for its essential oils and as an ornamental. This species is a representative of the genus with a derived staminal lever in the sense of Himmelbaur and Stibal [29]. The lever is spoon shaped and blocks the flower entrance completely (Figure 6.2B and Figure 6.7B). In 2003 and 2004, we observed flower-visiting insects on S. sclarea in the Freiburg Botanical Garden and in private gardens in Boetz-ingen (southwestern Germany) and Schwanau (southwestern Germany) where this plant was cultivated. Clary sage is visited mainly by carpenter bees Xylocopa violacea and, as in S. glutinosa, not by honeybees or other midsized bees (Table 6.1).

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