Osmia cornifrons Radoszkowski (Hymenoptera: Megachilidae), also known as the Japanese orchard bee, is an effective orchard pollinator. Considering honey bee population decline in the recent years, the conservation and propagation of O. cornifrons as an alternative managed pollinator is important in ensuring adequate pollination of tree fruit crops in the eastern United States. A field study was conducted to determine if nest manipulations could reduce mite parasites and parasitoid natural enemies that attack managed O. cornifrons. Paraffin-coated paper liners (straws) were added to create modified nests, and were compared with the unmodified nests (i.e., nests without paper liners). In each nest, we recorded the number of nest cells with cleptoparasitic mites (Chaetodactylus krombeini Baker) and the presence of a parasitoid wasp (Monodontomerus obscurus Westwood). We also recorded number of cocoons, males and females, as well as the number of unconsumed pollen-nectar provision masses in these nests.
Results showed that using paper liners in nest tunnels greatly reduced the impact of natural enemies of managed populations of O. cornifrons. Most notably, addition of paper liners provided protection from invasion by C. krombeini mites, as the mean number of nest cells with mites were significantly lower in these lined nests compared to the nests without paper liners. Significantly higher number of O. cornifrons male and female cocoons were recorded in the nests with paper liners. These results suggest that using nests with paper liners may accelerate O. cornifrons population establishment and propagation in commercial orchards of rosaceous fruit crops and possibly in other crops.