Apis mellifera and Megachile rotundata: a comparison of behaviour and seed yield in a hybrid carrot seed crop

The movement of managed alfalfa leafcutting bees (Megachile rotundata (F.)) in and around carrot flowers is compared with that of the honey bee (Apis mellifera L.) in a field trial to assess their relative efficacy as pollinators of hybrid carrot seed crops. Seed set is measured on carrot flowers inside cages with and without alfalfa leafcutting bees and compared with seed set in open field conditions in the presence of honey bees. Non-caged alfalfa leafcutting bees spend a similar amount of time on umbels and visit a similar number of umblets per umble as honey bees. Seed yield (number and weight of seeds) for flowers pollinated by caged alfalfa leafcutting bees is similar to that of flowers pollinated mainly by honey bees. However, it is not known how effective alfalfa leafcutting bees are compared with honey bees when not confined in cages (i.e. open pollination) under a range of commercial field conditions, particularly in the absence of plant species preferred by alfalfa leafcutting bees.