Pollinating Efficacy of Osmia cornifrons and Osmia lignaria subsp. lignaria (Hymenoptera: Megachilidae) on Three Brassicaceae Species Grown Under Field Cages

Until 1997, honey bees, Apis mellifera L., were used to pollinate Brassicaceae grown in field cages at the North Central Regional Plant Introduction Station (NCRPIS), at Ames, IA. At this time, a solitary bee, Osmia cornifrons (Radoszkowski), was first employed to pollinate the crop in field cages; however, a native bee species, Osmia lignaria subsp. lignaria Say, out-competes O. cornifrons in central Iowa for artificial nesting sites erected for rearing. The purpose of this study was to investigate the efficacy of these two solitary bee species for producing Brassica napus, B. rapa, and Sinapis alba seed in field cages. There was no difference in seed production for the S. alba accession, PI 209022, or the B. rapa accession, PI 278766, between the two species of Osmia. But, the B. rapa accession, PI 392025, and the B. napus accession, PI 469944, produced significantly more seed when pollinated by O. lignaria subsp. lignaria than by O. cornifrons. Because the native bee is easier to rear and maintain, it will be the pollinator of choice for control pollinating collections of Brassicaceae species maintained at NCRPIS. The commercial use of O. lignaria subsp. lignaria or the related subspecies, O. lignaria subsp. propinqua, should be investigated for improving the production of canola and rapeseed.