Management of Osmia lignaria (Hymenoptera: Megachilidae) populations for almond pollination:: Methods to advance bee emergence

The objective of this study was to find one or more rearing methods that would allow us to release Osmia lignaria Say populations from natal nests to pollinate February-flowering almonds, Prunus amygdalus Batsch, in California's Central Valley. We exposed three phenologically distinct O. lignaria populations (early-, mid-, and late-flying) to different temperature treatments through development and wintering for a total of nine rearing treatments. These treatments combined three approaches to obtain early Lee emergence: (1) exposing bees to warmer or fluctuating temperatures, or both, during development; (2) exposing bees to warmer wintering temperatures: and (3) using early-flying lee populations from Central Valley California latitudes. Extended periods of high prewintering temperatures resulted in apparent fat bod, consumption of prewintering adults and reductions in springtime adult longevity. In general, temperature treatments that promoted rapid immature development, and thus longer wintering periods, resulted in earlier spring emergence patterns of bees well timed with bloom period of almonds. Warmer wintering periods also resulted in earlier emergence. In addition to providing good Ice-bloom synchrony, several treatments also yielded vigorous emerging populations, rapid establishment and nesting, and population increases. The potential importance of our results to anticipated increases in the demand for pollination services in California's Central Valley almonds is discussed.