We collected four species of Osmia spp. consisting of O. cornifrons, O. pedicornis, O. taurus and O. satoi in Yeongwol, Bonghwa and Yechon locations. O. pedicornis was the dominant species, which accounts for 59.6% to 76.4% in the three locations. The sex ratio of Osmia spp. were from 1:1 to 1: 2.8 in O. cornifrons and from 1:2.8 to 1: 5.5 in O. pedicornis. The sex ratio of O. cornifrons and O. pedicornis was different in 3 locations. The female and male cocoons of O. cornifrons were the long elliptical-shaped and grey-brown color. The female and male cocoons of O. pedicornis were the long elliptical-shaped and polished dark-brown color. In both species of O. cornifrons and O. pedicornis, the cocoon size of the females was significantly larger than that of the male. Between those two species, the latter had a relatively bigger size than the former.

Bees of the genus Osmia are cavity-nesting solitary species that play important roles as pollinators. Nest traps are one of the most common methods to study Osmia bees. To elucidate the optimal environmental conditions of nesting sites, we investigated the effects of location, direction, altitude, and sites of nest traps on the rate of trap-nesting Osmia spp. During the collection period, the average rate of trap-nesting Osmia spp. collected within 90 days after the installation of traps was 17.0±20.0%. This percentage was 2.7-fold higher than that of trap-nesting bees in 30 days after the installation of traps. The Jeongseon location exhibited the highest rates of trap-nesting Osmia spp. collected in 30 and 90 days, representing 11.1 ±17.6% and 23.2±22.5%, respectively. The direction of the nest traps did not affect the rate of trap-nesting Osmia spp. The altitude ranges of the traps were 0-199 m, 200-399 m, 400-599 m, 600-799 m and over 800 m. Interestingly, the altitude range of 600-799 m showed the highest rate of trap-nesting bees, which was 40.4±3.9%. Higher altitudes seemed to correspond to higher rates of trap-nesting bees. With regards to the sites where the nests were placed, the rate of trap-nesting bees in a mud wall of an old house was 45.1±25.2%, which was 3-fold higher than that of a nest in an apple orchard. The flowering plants collected at different locations during the trap-nesting activity of Osmia bees belonged to 18 families and 34 species. In conclusion, the rates of trap nests colonized by Osmia spp. were affected by altitude, site, and plant diversity.