Potential use of the alfalfa leafcutter bee Megachile rotundata to pollinate sweet clover

Abstract

SUMMARYThe effectiveness of the alfalfa leafcutter bee, Megachile rotundata, as a potential pollinator of biennial yellow sweet clover, Melilotus officinalis, and biennial white sweet clover, Melilotus alba, and its potential to reproduce on the crop were evaluated over a 2-year period. Populations of the most important pollinator of the crop, the honey bee, Apis mellifera, continue to decrease in North America, thus there is a need to evaluate alternative pollinators so that seed growers can optimize their choice of pollinator. Treatments consisted of plants caged to exclude all pollinators, plants caged with leafcutter bees, and plants exposed to all resident pollinators including alfalfa leafcutter bees. The sweet clovers were essentially self-sterile and produced very little seed when bees were excluded. Percentage seed set and yield were higher for plants exposed to resident pollinators compared to plants caged with leafcutter bees, except in one year for yellow sweet clover. The propagation rate and quality of alfalfa leafcutter bees produced on sweet clover was excellent. The alfalfa leafcutter bee can be recommended as an effective pollinator of sweet clover, thus increasing the options available to seed growers and beekeepers regarding choice of pollinator.