Technical Abstract: Since the 1970's it has become ever harder for U.S. alfalfa seed producers to increase Megachile rotundata populations used for alfalfa pollination. In 1998, we monitored M. rotundata population dynamics and foraging behavior, as well as alfalfa bloom, pollination rates and seed yields in two fields in eastern Oregon. Despite marked differences in bee management, establishment was very similar in the two fields (~0.5 females per nesting cavity), and lagged peak bloom by 2 weeks. Pollination rates increased from 0-10% in the first two weeks to 80-90% in weeks 4-5. By then, it was difficult for M. rotundata females to find untripped (non-pollinated) flowers. Megachile rotundata progeny mortality was 54-78%. Seed yields were very high (~2200 kg/ha) in both fields. We contend that similar seed yields, and improved bee production, could be accomplished with smaller bee populations, better timed with alfalfa bloom.