The Solitary Bees by Danforth Bryan N.; Minckley Robert L.; Neff John L

Author:Danforth, Bryan N.; Minckley, Robert L.; Neff, John L.
Language: eng
Format: epub
Publisher: Princeton University Press
Published: 2019-05-28T16:00:00+00:00

RARITY, VULNERABILITY, AND IMPORTANCE AS BIOINDICATORS

Brood-parasitic bees are generally rare, and there is good reason to think that they may be more prone to local extinction than their solitary pollen-collecting hosts. Brood parasites are entirely dependent on the presence of one or more host species, they are often host-specific, their population numbers are usually low (sometimes very low) relative to their hosts, and they would seem to be rather poor dispersers. That brood parasites can be extremely rare is illustrated beautifully by Epeoloides pilosulus, a brood parasite of Macropis nuda.

E. pilosulus is a very rare bee. It is the sole member of the genus Epeoloides in the Western Hemisphere (there is another species in Europe), and it has gone uncollected for decades. It was, in fact, thought to be extinct because specimens had not been collected in North America since the 1960s. However, Cory Sheffield collected two male specimens in Nova Scotia, Canada, in 2002 (Sheffield et al. 2004), Sheffield and Heron (2018) reported on a single specimen collected in Alberta, and Achik Dorchin from Cornell University collected a single male in New York State in 2014. We should point out that Macropis is not your average bee. The genus Macropis includes a handful of species (16) ranging from North America to Europe and eastward to China (Michez and Patiny 2005). Macropis is an oil-collecting bee that relies exclusively on Lysimachia plants for its floral oils, which are mixed into the provision mass and used to waterproof brood cells. Macropis is a rare bee by most standards. They can be found only along the edges of streams, ponds, and lakes, where their oil-producing host plant is present. The rarity and narrow ecological preferences of Macropis would certainly explain the rarity of E. pilosulus in North America. But is E. pilosulus on the verge of extinction? We really don’t know. Perhaps this rare tripartite relationship between host plant (Lysimachia), pollinator (Macropis), and parasite (E. pilosulus) has always been rare and managed to hang on due to some remarkable dispersal (and recolonization) abilities of host and parasite. Alternatively, perhaps we are witnessing the steady decline and disappearance of one of North America’s most fascinating bees.

Because brood-parasitic bees represent the apex of bee communities, the diversity and abundance of brood parasites relative to other bees might be a good indicator of the status of the entire bee community. This idea was suggested by Cory Sheffield and coauthors (2013) based on studies of native bee communities in apple orchards. Sheffield surveyed bees in apple orchards and adjacent areas in the Annapolis Valley, Nova Scotia, in 2001 and 2002 using “yellow pan traps,” a common method for surveying bees. He sampled 19 sites over a range of habitat types from relatively undisturbed sites (unmanaged meadows and abandoned orchards) to heavily disturbed sites (commercially managed apple orchards). Overall, he detected 146 native bee species. He found that brood-parasitic bees were diverse and abundant in old fields and abandoned orchards, but were nearly absent in heavily managed commercial orchards.

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