Interactions between floral resources and bees (Hymenoptera : Megachilidae) in commercial alfalfa seed fields

We monitored flower resources around 9 Megachile rotundata (F.) bee shelter s in 7 commercial seed fields of alfalfa, Medicago sativa L. (Leguminosae) seed fields to understand better the interactions between floral resources and bee pollinators. A composite pattern of floral resource availability de monstrated an initial burst of bloom, followed by a linear decline in total flowers per raceme and an exponential decline in numbers of racemes with o pen flowers over the season. Open flowers per raceme declined exponentially at a more rapid rate than did total flowers per raceme, and standing crop of nectar sugar declined even more rapidly. Thus, floral resources availabl e to bees declined to low levels within 3-4 wk of bee introduction. Pollina tor activity was relatively constant within a week or 2 of release of bees into the fields. Numbers of open flowers and nectar availability declined m ore rapidly close to bee shelters than at a distance fi-om them. We interpr et the rapid decline in floral resources partly as a result of steady polli nation over time. The decline in floral resources may contribute to poor be e yields in alfalfa seed fields.