Nest architecture and pollen hosts of the boreoalpine osmiine bee species Hoplitis (Alcidamea) tuberculata (Hymenoptera, Megachilidae)

Andreas Müller

doi:10.3897/jhr.47.7278

Abstract

Although Hoplitis tuberculata is a rather common bee species in the upper montane and subalpine zone of the Alps, its biology is only fragmentarily known. In the present publication, both nest architecture and pollen host spectrum are described. H. tuberculata nests in insect borings in dead wood, where one to several brood cells are built in a linear series. Examination of four nests obtained from trap nests revealed three peculiar characteristics of its nest architecture: i) the 0.3-0.5 cm thick partitions between the brood cells are three-layered consisting of two walls built from masticated leaves which enclose an interlayer that is densely packed with pebbles, earth crumbs and other small particles; ii) in the majority of the nests, a vestibule varying in length from 2.2-8.9 cm and loosely filled with small particles is present between the outermost cell partition and the nest plug; iii) the nest is sealed by a 1.2-1.9 cm long plug consisting of two walls of masticated leaves which enclose a space that is densely packed with small particles and divided up by one to three additional walls. The nest architecture of H. tuberculata is unique among Palaearctic osmiine bees; however, it corresponds to that of three North American species closely related to H. tuberculata. Microscopical analysis of female pollen loads and brood cell provisions revealed that H. tuberculata is polylectic with a strong preference for Fabaceae. Among the Fabaceae, Lotus and Hippocrepis were by far the most important pollen hosts. Non-Fabaceae taxa represented by substantial proportions in pollen loads or cell provisions were Helianthemum (Cistaceae), Vaccinium (Ericaceae) and Rubus (Rosaceae).

Highlights

Hoplitis (Alcidamea) tuberculata is a boreoalpine species, which has a disjunct distribution area encompassing the Alpine arc from France to Austria and some neighbouring mountains such as Jura and Schwarzwald on the one hand and the boreal zone from Scandinavia and northeastern Europe to easternmost Asia on the other hand (Tkalců 1977, Müller 2015). It belongs to a clade of six species, which were formerly treated as members of the subgenus Monumetha (Michener 2007, Ungricht et al 2008), but recently merged as Hoplitis tuberculata species group into the large subgenus Alcidamea (Sedivy et al 2013c, Müller 2015)
While H. tuberculata is restricted to the Palaearctic region, all the other species occur in North America with some species reaching as far north as arctic Alaska (Michener 1947, 2007, Hurd and Michener 1955, Ascher and Pickering 2015), clearly suggesting a nearctic origin of the Hoplitis tuberculata species group (Sedivy et al 2013c)
Based on the investigation of four nests recently discovered in the Swiss Alps and the microscopical analysis of 87 pollen loads of females collected across the Alpine arc, the present publication aims to fill the knowledge gaps still existing on both the nesting biology and the flower preferences of Hoplitis tuberculata

Summary

Introduction

Osmiine bees are famous for their very diverse and often spectacular nest building behaviours as well as for their high proportion of species that exhibit narrow host plant specializations (Friese 1923, Malyshev 1937, Westrich 1989, O’Toole and Raw 1991, Müller et al 1997, Cane et al 2007, Sedivy et al 2008, 2013a,b,c, Gotlieb et al 2014, Haider et al 2014, Müller 2015). Hoplitis (Alcidamea) tuberculata is a boreoalpine species, which has a disjunct distribution area encompassing the Alpine arc from France to Austria and some neighbouring mountains such as Jura and Schwarzwald on the one hand and the boreal zone from Scandinavia and northeastern Europe to easternmost Asia on the other hand (Tkalců 1977, Müller 2015) It belongs to a clade of six species, which were formerly treated as members of the subgenus Monumetha (Michener 2007, Ungricht et al 2008), but recently merged as Hoplitis tuberculata species group into the large subgenus Alcidamea (Sedivy et al 2013c, Müller 2015). Based on the investigation of four nests recently discovered in the Swiss Alps and the microscopical analysis of 87 pollen loads of females collected across the Alpine arc, the present publication aims to fill the knowledge gaps still existing on both the nesting biology and the flower preferences of Hoplitis tuberculata

Material and methods

Results

Discussion