A new bee species that excavates sandstone nests

Authors: ORR, MICHAEL - Utah State University; Griswold, Terry; PITTS, JAMES - Utah State University; PARKER, FRANK - Retired ARS Employee

Submitted to: Current Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/19/2016
Publication Date: 9/12/2016
Citation: Orr, M.C., Griswold, T.L., Pitts, J., Parker, F.D. 2016. A new bee species that excavates sandstone nests. Current Biology. 26(17):792-793.

Interpretive Summary: Bees nest in a wide variety of substrates, from the soil in your garden to the ash beside volcanic craters. Trade-offs between the costs and benefits of potential nesting sites theoretically determine where bees nest, but these factors are often difficult to discern. We performed field and lab studies on the new species Anthophora pueblo, discovered nesting in sandstone, to better understand how and why bees use challenging nest substrates. We repeatedly found dense groups of nests in softer sandstone, indicating that hardness limits where they can nest. Nesting so closely may incur additional costs. High densities of nests may lead to nest-site competition and aggregations may attract parasites. However, evidence for benefits was found through rearing adults from two sandstone samples in the lab. While most bees develop over winter and emerge the following year, A. pueblo emerged over the course of five years without ever re-nesting. As sandstone nests are more durable, they likely provide better protection against flash floods and other damage over time, making delayed emergence less risky. Nesting is sandstone may also reduce parasite levels. Though the dominant parasite of A. pueblo, the beetle Tricrania stansburii, inhabited nearly 50% of all cells in 1980, it accounted for <10% in the 1982 sample. This was likely due to the fact that most beetles died in their cells, unable to emerge through the sandstone. Further research is necessary to confirm and quantify the costs and benefits of nesting in sandstone. Nonetheless, there are many ways in which the benefits of nesting in sandstone may outweigh the costs.

Technical Abstract: Many wonder why animals act in seemingly injurious ways. Understanding the behavior of pollinators such as bees is especially important because of the necessary ecosystem service they provide. The new species Anthophora pueblo, discovered excavating sandstone nests, provides a model system for addressing these confounding behaviors. Given the costs inherent to sandstone excavation and high nest density, and the challenges of living in a desert, offsetting benefits are expected. We investigated possible benefits through novel application of interdisciplinary methodologies in field and lab studies at seven sites spanning almost four decades. As this species prefers weaker sandstone and re-uses tunnels, what appeared to be a cost becomes a benefit: the substrate’s durability has enabled them to persist at one site longer than any other published bee nest aggregation. This also lessens costs to delaying their emergence, a bet-hedging strategy used to avoid years with poor floral resources. Similarly tracking their host, two parasites also delayed their emergences, including the first definitive record for parasitic bees. Though sandstone does not eliminate nest invasion, as evidenced by the 20 other species inhabiting this unique ecosystem, sandstone appears to control parasite buildup across years and perhaps influences the microbial community. Microbes may play a larger role for Anthophora pueblo than other solitary bees, as we record here the first instance of pathogenic chalkbrood in a non-megachilid, solitary bee. Despite the costs, Anthophora pueblo appears to have struck a balance between sandstone and its xeric environment that is beneficial overall.