Floral preferences of Megachile rotundata across a landscape gradient from agriculture to wild lands

Megachile rotundata (the alfalfa leafcutting bee) is the most intensively managed solitary bee used as a commercial pollinator for agricultural production. Introduced from Eurasia to the United States by the 1940’s, M. rotundata tripled North American alfalfa seed production. Beyond its preference for alfalfa, M. rotundata are considered versatile in foraging and pollinating behavior; however, relatively little is known about floral preferences in non-alfalfa landscapes. Here we examined the floral preferences in five landscape types: Agriculture, Urban Agriculture, Urban, Semi-wild Agriculture and Wild landscapes. We released 1 “bee gallon” of M. rotundata (approximately 10,000 bees) at each of the five sites, four out of the five sites (sans wild site) were near established Dalea plots. Every week, for seven weeks, we took fully completed nests from provided bee boards to compare pollen compositions from mass provisions between landscapes and over the growing period. We found three main results. 1) M. rotundata selected pollen from the family Fabaceae over other available plants such as asters, yarrow and bindweed in all landscapes. 2) Dalea comprised only 20% of the pollen in the provision, despite being the closest available legume. 3) Although these bees were not placed in the direct vicinity of alfalfa fields, alfalfa pollen made up more than half the provision masses at the agriculture, urban-agriculture and wild sites. These results reinforce the idea that M. rotundata has the potential to be a good managed pollinator for both alfalfa and non-alfalfa legume crops.