Corresponding author: Andreas Müller (
Academic editor: Jack Neff
Although
Müller A (2015) Nest architecture and pollen hosts of the boreoalpine osmiine bee species
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 (
Nesting biology of
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
In spring 2014 and 2015, a total of 20 trap nests were fixed at a height of 0.2-1.5 m to sun exposed dead wood in an open subalpine forest above Sedrun (Grisons, Switzerland) between 1650 m and 1800 m a.s.l., where
To uncover the pollen host preferences of
Four nests of
All four nests built in the bamboo sticks of the trap nests had a similar structure and consisted of i) a basal wall that sealed the nest against the rear end, ii) a varying number of brood cells each delimited towards the nest entrance by a cell partition, iii) a (facultative) vestibule in front of the last cell and iv) a nest plug that closed the nest at the front end. The distance from the basal wall to the outermost wall of the nest plug was 6.5 cm, 7.6 cm, 8.3 cm and 10.9 cm.
The basal walls consisted of masticated leaves (“leaf pulp”) and had a width of about 1 mm. In two nests, a free space between pith and basal wall with a length of 0.4 cm and 3.5 cm, respectively, was present, which was loosely filled with small particles, such as pebbles, wood and leaf fragments, seeds or earth crumbs (Fig.
Nest architecture of
The four nests contained one (n=1), two (n=2) and four (n=1) linearly arranged brood cells, which had a length of 8.5-12.5 mm (Fig.
Three of the four nests contained a vestibule between the outermost cell partition and the nest plug measuring 2.2 cm, 8.1 cm and 8.9 cm in length (Fig.
The nest plugs measured 1.2 cm, 1.3 cm, 1.4 cm and 1.9 cm in length. They consisted of one wall each at the rear and the front end, which enclosed a space that was divided up by one (n=1) or three (n=3) additional walls (Fig.
In summary, the females used two different materials for nest construction: i) leaf pulp to build all the walls within the nest (Fig.
The microscopical analysis of 87 female pollen loads revealed that
Pollen composition of female pollen loads of
Plant family | Plant genus/ subfamily | % pollen grain volume | number (%) of loads with this pollen type | number (%) of pure loads |
---|---|---|---|---|
|
84.5 | 87 (100) | 54 (62.1) | |
|
|
63.9 | 84 (96.6) | 35 (40.2) |
|
|
11.0 | 31 (35.6) | 0 (0) |
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2.9 | 3 (3.4) | 0 (0) |
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1.4 | 2 (2.3) | 0 (0) |
|
unknown | 5.2 | 7 (8.0) | 0 (0) |
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|
8.9 | 16 (18.4) | 0 (0) |
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|
1.3 | 2 (2.3) | 0 (0) |
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0.9 | 2 (2.3) | 0 (0) |
|
1.2 | 6 (6.9) | 0 (0) | |
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0.7 | 5 (5.7) | 0 (0) |
|
|
0.5 | 1 (1.1) | 0 (0) |
|
|
0.5 | 2 (2.3) | 0 (0) |
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|
0.5 | 3 (3.4) | 0 (0) |
|
0.4 | 2 (2.3) | 0 (0) | |
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|
0.4 | 1 (1.1) | 0 (0) |
|
|
0.05 | 1 (1.1) | 0 (0) |
unknown | 1.8 | 4 (4.6) | 0 (0) |
Pollen of
Pollen composition of brood cells of
Nest 1 | Brood cell 1 | ++++ | ++++ | ++++ | |||
Brood cell 2 | ++++ | ++++ | ++++ | ||||
Nest 2 | Brood cell 1 | ++++ | +++ | ++++ | ++ | ||
Brood cell 2 | +++++ | +++ | ++ | ||||
Brood cell 3 | +++++ | ++ | + | +++ | ++ | ||
Brood cell 4 | +++++ | ++ | +++ | + | ++ |
As shown in the present study,
Peculiar characteristics of the nest architecture of
The construction of three-layered cell partitions composed of two walls with an interlayer of densely packed small particles in between seems to be unique among Palaearctic osmiine bees, which usually partition linearly arranged brood cells by single walls only (
The function of the three-layered cell partitions is counterintuitive at first sight as the thick nest plug built by
The presence of a vestibule filled with small particles seems to be another typical trait common to the members of the
The architecture of the nest plug varies both within and among the North American members of the
In summary, although the nest architecture of
The present study shows that
In summary, the pollen hosts of
F. Gusenleitner (Biologiezentrum Linz), U. Weibel (Museum Allerheiligen Schaffhausen) and M. Schwarz (Ansfelden) allowed removal of pollen from collected specimens. J. van Leeuwen (University of Bern) helped with pollen identification. F. Amiet (Solothurn) provided Figure