Effectiveness of the alfalfa leafcutter bee Megachile rotundata Fab. to pollinate perennial clovers

Abstract

The effectiveness of the alfalfa leafcutter bee, Megachile rotundata Fab., as a pollinator of alsike clover (Trifolium hybridum), red clover (Trifolium pratense), white clover (Trifolium repens), and zigzag clover (Trifolium medium), and its ability to reproduce on alsike clover and white clover were evaluated. Populations of the most important pollinators of the crop, the honey bee, Apis mellifera L., and various bumble bee species, Bombus sp., 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 the alfalfa leafcutter bee. These perennial clovers were essentially self-sterile, and produced very little seed when bees were excluded. Percentage seed set and yield were higher, or at least equal, for plants exposed to resident pollinators compared to plants caged with leafcutter bees in all years and for all plant species. The propagation rates and quality of alfalfa leafcutter bees produced on alsike clover and white clover were excellent. The alfalfa leafcutter bee can thus be recommended as an effective pollinator of alsike clover, red clover and white clover, increasing the options available to seed growers and leafcutter beekeepers regarding choice of pollinator. Seed set and seed yields in zigzag clover were low for both open pollinated and caged treatments; alfalfa leafcutter bees marginally contributed to seed set or yield.