The ability of high- and low-grooming lines of honey bees to remove the parasitic mite Varroa destructor is affected by environmental conditions

Abstract

This study assessed how variation in temperature and humidity affect the costs and benefits of grooming as a defense against Varroa destructor Anderson and Trueman, 2000 in high-grooming and low-grooming groups of honey bee (Apis mellifera L., 1758) workers. Grooming was quantified as the proportion of mites falling to the bottom of cages containing worker bees or to the bottom of colonies of bees during winter. Cages of 100 mite-infested bees from each line of workers were assigned to environments with three treatment combinations of temperature (10, 25, and 34 °C) and humidity (low, medium, and high), and bee and mite mortality rates were quantified. The results showed relative effectiveness of high- and low-grooming groups being affected by the environment. Differences in grooming between lines were greatest at 25 °C and were slightly higher under conditions of low humidity than at higher levels. Mite mortality rates were greater in high-grooming groups of caged bees than in low-grooming bees held at 25 and 34 °C but were similar at 10 °C. During winter, colonies with high-grooming bees had higher daily mite mortality rates than unselected colonies. Bee mortality rates were greater in high-grooming lines than in low-grooming lines under low temperatures, indicating that there may be a biological cost associated with grooming behaviour at low temperature.