Persistent nesting by Anthophora Latreille, 1803 (Hymenoptera: Apidae) bees in ash adjacent to an active volcano

Ground-nesting bees use a variety of substrates in which to establish cells and complete their reproductive cycles. Here we document the highly aberrant occurrence of a solitary bee species, Anthophora squammulosa Dours, 1870 (Hymenoptera: Apidae: Anthophorini), nesting within meters of an active volcanic crater in Nicaragua, Central America. The nest location is exposed to continuous, strongly acidic gas emissions (>2.7 ppm of SO2), and sporadic vent clearing episodes that blanket the surrounding area with ash and tephra. An assessment of floral resources available within the expected homing distance of the species was cross-referenced with pollen carried by females returning to their nests. At this site, A. squammulosa appears to forage almost exclusively on a single plant, Melanthera nivea (L.) Small, 1903 (Asteraceae), that is adapted to volcanic acidic rain, despite being widely accepted as a generalist bee in the remainder of its range. Notwithstanding the extreme nature of the site, and the co-occurrence of specialist natural enemies and predators, the possibility exists that the site is selected for its beneficial attributes, such as the loose, well-drained substrate and the absence of vegetation. The converse is that the site is sub-optimal with the population constrained by habitat patchiness and limited dispersal options.