Nesting cavity diameter has implications for management of the alfalfa leafcutting bee (Hymenoptera: Megachilidae).

Body size influences performance in many bee species and may be influenced by nesting cavity diameter in cavity-nesting bees. Megachile rotundata (Fabricius) (Hymenoptera: Megachilidae) is a commercially-managed, solitary cavity-nesting bee. In M. rotundata body size has low heritability and is strongly influenced by the size of the larval provision and the diameter of the nesting cavity. Commercial nesting boxes have cavities that are 7 mm in diameter. Our goal was to examine the effects that nesting cavity diameter has on M. rotundata body size and performance by manipulating the size of cavities that are available for nesting. We provided bees with nesting cavities that ranged in size from 4 to 9 millimeters in 1 mm increments. To assess body size we measured mass and intertegular span. To assess performance we measured wing area, wing loading, sex, overwintering survival, pollen ball occurrence, and diapause status in the offspring. We also examined the reproductive output from the different nest cavity diameters. We found that the 8 mm cavities reared bees with the largest mass, and 4 mm cavities reared bees with the smallest mass. We determined that the 7 mm nesting cavity is optimal for offspring yield, the 8 mm nesting cavity is optimal for performance, and the 5 mm nesting cavity may be optimal for conservation efforts of other cavity-nesting bees. Based on the desired outcome of the bee managers, nest sizes differing from the standard may provide an advantage.

Telomere length is longer following diapause in two solitary bee species.

The mechanisms that underlie senescence are not well understood in insects. Telomeres are conserved repetitive sequences at chromosome ends that protect DNA during replication. In many vertebrates, telomeres shorten during cell division and in response to stress and are often used as a cellular marker of senescence. However, little is known about telomere dynamics across the lifespan in invertebrates. We measured telomere length in larvae, prepupae, pupae, and adults of two species of solitary bees, Osmia lignaria and Megachile rotundata. Contrary to our predictions, telomere length was longer in later developmental stages in both O. lignaria and M. rotundata. Longer telomeres occurred after emergence from diapause, which is a physiological state with increased tolerance to stress. In O. lignaria, telomeres were longer in adults when they emerged following diapause. In M. rotundata, telomeres were longer in the pupal stage and subsequent adult stage, which occurs after prepupal diapause. In both species, telomere length did not change during the 8 months of diapause. Telomere length did not differ by mass similarly across species or sex. We also did not see a difference in telomere length after adult O. lignaria were exposed to a nutritional stress, nor did length change during their adult lifespan. Taken together, these results suggest that telomere dynamics in solitary bees differ from what is commonly reported in vertebrates and suggest that insect diapause may influence telomere dynamics.