Colony Survival: A Better Bee or a Milder Mite?

AMERICAN BEE JOURNAL, VOLUME 139 NO. 9, September 1999

The use of any poison to control varroa serves only a stopgap measure. That is why we have seen much research effort these past decades, world-wide, to seek or breed a European honey bee strain resistant to those mites.

At the same time, we curiously have colony survival in some remote regions where neither chemical treatments nor managed colonies exist. A question thus arises: Is the honey bee colony rebound in remote areas due to survival of mite resistant bee colonies or due to selection toward a weaker strain of varroa mites?

Consider the situation here in Santa Barbara, a city that stretches from the ocean halfway up to the top of the nearly mile high mountain range close behind. Our city also has an ordinance against beekeeping. Behind Santa Barbara one finds a vast area of U.S. National Forest and designated wilderness areas. Few or no roads exist in most of that area. The constant threat of wildfires means that few beekeepers would risk using locations there – if they could obtain permission. Hence, any resurgence of colonies in that area would not likely have arisen by swarms escaping from managed colonies.

After varroa mites first arrived in the late 1980s in the Santa Barbara area, honey bee visitation to blossoms in urban gardens plummeted to a near absence, as it did in the back country. However, feral honey bee colonies have rebounded in both areas these past few years, with documented survival of some colonies over several years and a large number of swarms reported by residents during the last two years. A two story shingle-sided Boy Scout house in Manning Park, for example, currently has eight colonies in its walls. Inspection of a few of the older surviving feral colonies has revealed a low incidence of varroa mite infestation, with most of the reproduction in drone cells and very little in worker cells.

While many might favor the conclusion that feral bee colonies in this area may have become resistant to varroa mites, one can consider another hypothesis – milder mites. Varroa mites go through many generations each year, and we apparently have more than one strain in this country already. Even with brother-sister matings, a strong selection pressure might have impacted the varroa mites more than honey bees in our vast unpopulated area; the genetically most lethal mites could have been outcompeted by a less virulent strain. If so, feral colonies and mites in our back country could have achieved an accommodation due to a change in the biology or genetic strain of varroa rather than (or as well as) in the honey bees.

One can see where this thread might lead. We could perhaps exploit a weak strain of varroa mites as well as strive to find a mite-tolerant strain of honey bees. Time is of the essence in our area, however; the Africanized bees might well be here within a year!

Adrian M. Wenner
Santa Barbara, CA