Effect of Intertunnel Distance and Nest-Surface Aspect on Progeny Production Rate and Sex Ratio in the Alfalfa Leafcutting Bee (Hymenoptera: Megachilidae)

Populations of the alfalfa pollinator, Megachile rotundata (F.), nest in dense aggregations in artificial shelters in alfalfa fields. The closeness of the nest tunnels in these shelters (5–10 mm apart) fosters what appear to be numerous counterproductive interactions among females. By increasing the distance between nest tunnels and patterning the nest-block surface to help orient bees returning from foraging trips, we sought to reduce interactions and to increase both the number of progeny produced and the proportion of female progeny. Only the nest-block surface aspect affected progeny production rate; progeny were produced at a Significantly faster rate in patterned blocks than in plain blocks. Intertunnel distance did not affect progeny production rate. Nest blocks with tunnels 5 mm apart contained a significantly greater proportion of female progeny than did nest blocks with tunnels spaced farther apart. Sex ratio of progeny was unaffected by surface patterning of blocks. Females strongly preferred patterned to plain blocks and preferred 5-mm and 2-cm intertunnel distances to those of 4 cm. Beekeepers and alfalfa growers can increase bee productivity by supplying patterned nest blocks with intertunnel distances between 5 and 10 mm.