Convergent evolution of morphological specializations in Central European bee and honey wasp species as an adaptation to the uptake of pollen from nototribic flowers (Hymenoptera, Apoidea and Masaridae)

In the Central European apoid and masarid fauna, 13 bee species belonging to seven different taxonomic groups and one honey wasp species were found to be equipped with a specialized pollen-collecting apparatus on the face which is used to harvest pollen from nototribic flowers, viz. representatives of the Lamiaceae and the Scrophulariaceae. Pollen from these two plant families plays an important part in the larval nourishment of these hymenopteran species. The pollen-collecting apparatus consists of a peculiar facial pilosity composed of transformed hairs which are thickened at their base and either knobbed apically (Celonites abbreviatus) or extended into a thin tail which is either straight and bent at right angles ( Rophites spp., Anthophora borealis, A. furcata ) or wavy ( Anthidium spp., Anthocopa andrenoides, Osmia aurulenta, O. caerulescens ). Nototribic flowers are worked by pollen-collecting females by rubbing the facial area covered with the transformed hairs over the anthers (Celonites, Anthidium, Anthocopa, Osmia) , by buzzing the pollen amongst the transformed hairs (Anthophora Jurcata) or by a combination of rubbing movements and buzzing (Rophites) . Bee species lacking special morphological devices were observed to perform specialized behaviours when collecting pollen at nototribic flowers. Nototribic flowers, therefore, appear to be difficult to exploit for pollen. The raised position of the anthers in nototribic flowers as a possible means to reduce excessive pollen losses caused by pollen-collecting hymenopterans is discussed.