Abstract. 1. We investigated moth diversity and factors determining moth diversity on 17 islands in Dadohaehaesang National Park, South Korea. Moths were sampled from May to July 2009 using three UV light traps on each island.
2. A total of 431 species and 3,745 individuals in 17 families were identified; 83% of the total number of species and individuals identified belonged to the families Noctuidae, Geometridae, and Pyralidae.
3. To investigate the factors that determine moth diversity, we analyzed island area, maximum elevation, distance from the mainland, distance from the nearest island, distance from the nearest larger island, and the number of surrounding islands within 2 km using stepwise regression analysis. Plant community structure was included after transforming these data into six axes using principal component analysis.
4. The number of islands within 2 km was the primary factor explaining the observed moth diversity on the 17 islands. We showed that the equilibrium theory of island biogeography can be applied to moths of Korean offshore islands. Island area and distance from the mainland were also determinant factors of the observed number of species and number of individuals, respectively. These results suggest that protection of large islands together with the closest islands may maintain or preserve moth biodiversity in offshore islands of Korea.
5. While plant community structure did not explain moth diversity, the dominant moth species in each district had a dietary preference for perennial herbs or trees, indicating a preference for more stable resources.