Plants as indicators of leafcutter bee (Hymenoptera : Megachilidae) nest habitat in coastal dunes

To conserve native plants, pollinators and their nesting habitats must also be protected. Indicator plants for nesting sites of the native leafcutter bee Megachile wheeleri Mitchell were characterized within a Northern Califo rnia coastal dunes preserve. Nesting was restricted to the Poa-Lathyrus pla nt community. Significant positive associations were detected between bee n ests and Aira praecox L., A. caryophyllea L., Solidago spathulata DC., Junc us lesueurii Bolander, and mosses; negative associations with Carer obnupta L. Bailey and Lathyrus littoralis (Nuttall) Endlicher. Nest density and to tal plant cover were not significantly correlated. Nests were generally not constructed near the bee's host plants. Most nesting occurred in a zone tr ansitional between mesic lowlands and xeric higher elevations. Natural succ essional change was increasing nesting habitat, but climax shore pine-spruc e forest should eventually eliminate nesting habitat in the long term if su ccession is not disturbed. The introduced plants Lupinus arboreus Sims and Ammophila arenaria L. may eliminate nest habitat, but Aira praecox L. and A . caryophyllea L. may enhance it. Other bee and wasp species were present i n samples but no significant associations with plants were detected because densities were so low. Very large sample sizes will be required to determi ne significant associations for those species. M. wheeleri nests ranged fro m dense aggregations to scattered individual nests. Other bee and wasp spec ies also nested within M. wheeleri nest aggregations, including the sphecid wasp Bembix americana comata J. Parker, which normally nests in barren san d. Native plant restoration activities may benefit from restoration of nati ve pollinators.