Nest site orientation and relocation of populations of the orchard pollinator Osmia cornuta (Hymenoptera: Megachilidae)

Moving actively nesting populations of the orchard pollinator Osmia cornuta (Latreille) from a pollinated crop to one beginning to bloom could increase both the number of Bowers pollinated and the number of bee progeny produced. This study investigates the possibility of moving actively nesting O. cornuta populations, and evaluates the effects of moving distance and nest site artificial visual landmarks on orientation and establishment of moved females. Nesting shelters with known numbers of nesting females were nocturnally relocated for distances ranging from 0 to 240 km, and the numbers of nesting females were counted after each move. Nearly all females continued to nest at shelters that were moved short (0-3 m) distances. Moves of intermediate distances (135-235 m) resulted in considerable (30-76%) bee loss (dispersal), and many females new back to the original nesting site. At long distances (3-240 km), dispersal was higher (63-78%) and no bees were seen hovering at the original site. Moving distance was correlated positively with dispersal and with orientation (zigzagging) nights made by females when they first exited their nests after the moves. The addition or removal of supplementary visual landmarks (2 by 1.5-m banner with colored patterns) at the nesting shelter did not affect dispersal rates. Bees appeared to respond to supplementary landmarks but used other signals as primary orientation cues. An additional experiment showed that O. cornuta populations can be removed and stored at low temperature for up to 4 d (e.g., to avoid pesticide treatments) and then reinstalled at their nesting site, without affecting female orientation or nesting.