Host‐Plant Specialization in Western Palearctic Anthidine Bees (Hymenoptera: Apoidea: Megachilidae)

Abstract

To determine the extent of host—plant specialization, the pollen sources of the 72 anthidiine species (family Megachilidae, subfamily Megachilinae, tribe Anthidiini) of Europe, North Africa, and Asia Minor were investigated by microscopic analysis of ≈ 1800 pollen loads of females. By this measure, 31 species (43%) were oligolectic (relatively specialized to pollen source) at the level of plant tribe, plant subfamily, or plant family. Exclusive pollen sources of these bees throughout their geographic ranges are flowers of the Cardueae (Compositae), the Asteroideae (Compositae), the Papilionoideae (Leguminosae), the Lamioideae (Labiatae), the Nepetoideae (Labiatae), the Dipsacaceae, or the Campanulaceae. Thirteen species (18%) were found to exhibit a strong, but not exclusive, preference for the Papilionoideae (Leguminosae), the Labiatae, the Cardueae (Compositae), and Zygophyllum (Zygophyllaceae), respectively, while 25 species (35%) proved to be more markedly polylectic, visiting the flowers of up to 17 different plant families for pollen. The plants exploited by three species (4%) are insufficiently known. By far the most important pollen sources of the anthidiine bees as a whole are the Compositae (41.7%) followed by the Leguminosae (23.1%) and the Labiatae (13.0%). The phylogenetic relationships of the anthidiine bees were estimated by a cladistic analysis based on 115 characters to trace possible evolutionary patterns of diet composition. Based on the estimated phylogeny, at least eight shifts of oligoleges between different plant taxa and six transitions between oligolecty and polylecty appear to have occurred. Four transitions were from oligolecty to polylecty whereas two transitions are of unknown direction, both directions being equally parsimonious. Assuming that the ancestral state in the anthidiine bees was oligolectic, the present distribution of oligolectic and polylectic species can be explained solely by switches from the oligolectic to the polylectic habit and by shifts of oligoleges between different plant taxa. Three of four transitions from oligolecty to polylecty are accompanied by a reduction in bee body size. The significance of this size reduction with respect to the polylectic habit is discussed. The oligolectic anthidiine species visit significantly fewer flower species for pollen during a single foraging bout than the polylectic species. On average, 1.4 plant species were recorded in the loads of specialists compared to 2.2 for generalists. Two monophyletic groups of bees belonging to the genus Anthidium are equipped with a pollen—collecting apparatus consisting of specialized hairs localized either on the face or on the underside of the thorax. It is used to remove pollen from the raised anthers of flowers of the Labiatae and the Scrophulariaceae and to brush pollen from the flat inflorescences of some Compositae, respectively. The observation of flower—visiting females of several anthidiine species revealed that pollen uptake is far from an accidental process. Basic pollen—harvesting ...

Phylogeny and host-plant evolution in Melittidaes.l.(Hymenoptera: Apoidea)

“…Most cases of host-plant variation involve shifts in the host-plant visited with little change in diet breadth. This pattern is consistent with previous studies on the evolution of host-plant associations in bees (Müller, 1996a;Sipes and Tepedino, 2005;Patiny et al, 2007;Larkin et al, 2008).…”

“…However, several studies showed that field records are not always reliable enough to confidently determine the host-plant range because field records rarely distinguish between pollen and nectar foraging (e.g. Westrich and Schmidt, 1986;Westrich, 1990;Müller, 1996a;Sipes and Tepedino, 2005;Timmermann and Kuhlmann, unpubl. data.).…”

“…Pollen analyses allow the discrimination of pollen and nectar hosts, and the detection of inconspicuous floral choices. As a general rule, we sampled museum specimens in a way that maximised the species' temporal and spatial distribution (see details of method in Müller, 1996a). The pollen was gently removed with an insect pin and embedded in glycerol gelatine on microscope slides.…”

“…Only a few previous studies have examined the pattern of host-plant evolution in specialist bees using phylogenies at the species level (Müller, 1996a;Sipes and Wolf, 2001;Michez et al, 2004b;Sipes and Tepedino, 2005;Larkin et al, 2008). Such studies have generally indicated that host-plant associations are maintained over multiple speciation events (suggesting that host-switching is not always associated with speciation), but that when host switches occur, they occur to distantly related host-plant families.…”

Bee-flower association in the Neotropics: implications to bee conservation and plant pollination

“…According to the current theoretical framework, such generalist species are important to maintain the cohesion and stability of plant-bee networks (Memmott et al 2004). On the other hand, relationships between plants and bees may exhibit phylogenetic components that drive the preferences of a group of bees to a given group of plants (Müller 1996;Patiny et al 2008). Thus, certain bee taxa preferentially visit certain plant families or genera.…”