Observed Flower Visitors

During our observation periods, S. glutinosa and S. sclarea were visited only by a small number of bee species. Most of these (exceptions, e.g., the pollen and nectar thieves, Lasioglossum sp. and Hylaeus sp.) are already known to be flower visitors of S. glutinosa or S. sclarea (Table 6.1). Though there are numerous publications

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FIGURE 6.8 Force-distance diagrams showing the forces necessary to reach the nectar at the bottom of the corolla tube depending on different proboscis lengths. Series of measurements in the same flower of S. sclarea (internal flower-tube length 9.4 mm) using the modified sensor with an insect's head mounted at various distances from the sensor tip. Mimicked proboscis length (black to white, see insert): 11, 8, 7, 6, and 5 mm (in the latter measurement, the flower tube was destroyed at the end point of the force-distance curve marked with an x).

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FIGURE 6.8 Force-distance diagrams showing the forces necessary to reach the nectar at the bottom of the corolla tube depending on different proboscis lengths. Series of measurements in the same flower of S. sclarea (internal flower-tube length 9.4 mm) using the modified sensor with an insect's head mounted at various distances from the sensor tip. Mimicked proboscis length (black to white, see insert): 11, 8, 7, 6, and 5 mm (in the latter measurement, the flower tube was destroyed at the end point of the force-distance curve marked with an x).

on the pollination biology of these two Salvia species, there are no reports that honeybees have ever been seen triggering the staminal lever while foraging for nectar in flowers of these species (see Refs. [32-34] and our unpublished observations). The observation that only a small number of bee species visits these two sages supports the assumption that S. glutinosa and S. sclarea are specialized (in terms of species number of flower-visiting insects). Honeybees seem to be excluded from successfully (with regard to nectar feeding) visiting these flowers by either the staminal lever, the additional internal barriers, or the length of the flower tube.

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