The effect of honey bee (Apis mellifera) inter-colony distance on the spread of the parasitic Mite, Varroa destructor

The parasitic mite, Varroa destructor is transmitted horizontally in honey bees, Apis mellifera through both drifting and robbing between colonies. We were able to compare horizontal transmission over time among isolated apiaries, each comprised of two honey bee colonies spaced apart either 0, 10, or 100 meters. One colony in each apiary pairing was mite free (non-trojan) and one colony was seeded with 300 female Varroa (trojan). Rate of mite transmission was not significantly different among the three distances. At the end of 15 weeks, a significant reduction in colony mite populations was observed in the 100-meter colonies compared to the 0-meter and 10-meter apiaries. The detection of mites in non-trojan colonies at all distances 20 days after mites were introduced in trojan colonies suggests a rapid dissemination of mites. The loss of significant difference between trojan and non-trojan colonies at all three distances after 3 months suggests a high level of contact between colonies, probably due to high levels of drifting and robbing. This study emphasizes the importance of horizontal transmission to the host/parasite interaction between Varroa destructor and Apis mellifera. Future treatment programs should factor this high level of transmission into any management plan. This research also supports the theory that high levels of horizontal disease transmission selects for high parasite virulence.