Distribution of Chaetodactylus krombeini (Acari: Chaetodactylidae) within Osmia cornifrons (Hymenoptera: Megachilidae) nests: implications for population management.

Chaetodactylus krombeini (Baker) (Acari: Chaetodactylidae) is a cleptoparasitic mite that negatively affects propagation of Osmia spp. (Hymenoptera: Megachilidae) for orchard pollination in the USA. This study was conducted to determine the effect of C. krombeini on mortality of male and female Osmia cornifrons, the Japanese hornfaced bee. A total of 107 O. cornifrons nests were examined to determine within-nest distribution of C. krombeini with regression analyses. A total of 30 mite-free O. cornifrons nests were observed and within-nest distribution of male and female O. cornifrons was determined with non-linear regression analyses. In addition, cocoons from 20 mite-infested O. cornifrons cells were examined to determine whether C. krombeini could be found inside cocoons of O. cornifrons. The results of this study showed that female O. cornifrons and C. krombeini were found more frequently in the inner part of the nest, and male O. cornifrons were found mostly in the center of the nest. No C. krombeini were found inside O. cornifrons cocoons. These results indicate that C. krombeini have a greater negative impact on mortality in the egg and larval stages of female O. cornifrons than in male O. cornifrons. Implications for management of C. krombeini and O. cornifrons populations for orchard pollination are discussed in this article.