Forest Bees

As the first of two Somerset BKA special lectures, Thomas Seeley of Cornell University gave a fascinating and entertaining account of his investigations into the apparent ability of feral bees in a remote area of the US to thrive post-Varroa without any applied treatment.

Feral bees were believed to have been rendered extinct (as they are here) by the widespread Varroa infestation in the early nineties. In 1978, Professor Seeley mapped 11 wild colonies in the 4500-acre Arnot Forest, by trapping and tracking bees back to their homes high up in the secondary woodland. Resurveying in 2002, he found feral colony numbers undiminished. This presented the tantalising possibility of a naturally-evolved Varroa-resistant bee. Obtaining sample colonies using bait hives, he established that all had Varroa present, but at sub-lethal levels through the year. By experiment, he then tested whether this was due to the bees’ “resistance” to Varroa, or Varroa developing “avirulence” - the principle of a parasite keeping its level of impact sub-fatal to the host in order that the host and parasite can thrive together. Put simply, with only 11 colonies in 4500 acres, if the Varroa were sufficiently virulent to kill its host colonies, that line of Varroa genes would also die out. In an apiary situation, robbing, drifting and moving combs would probably allow such genes to persist. Comparing experimental bee colonies with “normal“ comparable colonies both deliberately infected with “standard“ Varroa, disappointingly he found no clear difference in tolerance. This suggested that the answer lay with the Varroa themselves developing avirulence in order to survive. This is perhaps logical when one considers the relatively slow genetic change rate of unmanaged bee-populations compared with numerous generations of Varroa over the same period.

Unfortunately, blanket domestic use of miticides tends to kill high proportions of Varroa across the population, making natural selection for sub-lethal habits less likely. The frustrating implication was that, if Varroa is now endemic, only by tolerating short-term losses at a potentially devastating scale in our normally closely grouped apiaries might we see Varroa similarly evolving in domestic stocks.

Pat Lehain

Somerton Beekeepers‘ News via BEES

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