Manipulating soil temperatures to influence brood emergence in the alkali bee (Nomia melanderi)

There are over 6,000 acres of alfalfa grown for seed in the Walla Walla Valley in Washington. Seed yields per acre in this growing district are typically substantially greater than other growing districts. This can be directly attributed to the efficient pollination efforts of alkali bees. Maintaining populations of alkali bees, Nomia melanderi, is crucial for alfalfa seed production. In the spring of 2009, temperatures in the Walla Walla Valley were cool, followed by a warm June and alkali bee emergence was delayed during the early alfalfa bloom. To allow for more efficient pollination, we manipulated soil temperatures with various powders including chalk dust, charcoal dust, and clear plastic in spring 2010 to determine if the use of these colored materials on the soil surface can change temperatures at depths between 6 and 12 inches. Each plot occupied a square meter with ten replicates of each treatment. As expected the clear plastic produced the earliest and most abundant emergence of adult bees, while the white chalk dust produced the lowest number of emergence holes throughout the early flight of the foraging bees. By expediting or postponing emergence with these treatments, growers can prolong the foraging season of alkali bees for efficient pollination over an extended period of time.