On its natural host, Apis cerana, varroa is a minor pest. Cerana has evolved a number of defenses against the mite—notably grooming behavior, infested worker brood removal, and trapping the mite in drone brood. These defenses allow the mite to coexist in the colony, but at low levels. This is an expected mature host/parasite relationship. The European honey bee, Apis mellifera, rarely showed any such traits when first infested with varroa, but these days we’re seeing the behaviors for chewing out infested brood and grooming more commonly.
If there had been no human intervention after varroa made the jump to the European honey bee (EHB), the vast majority of colonies would have died out, but, given a large enough population, and with enough genetic variability, the few survivors would likely have repopulated some or all of the range. The process would have been encouraged by the selective pressure against severely virulent strains of mite—they would have had a hard time dispersing over honeybee-impoverished areas without human assistance (robbing being critical to the dispersal of virulent mites).
Using mite resistant bees
So what is one to do? First, promote mite resistant queens, either by purchasing from a breeder/producer, or taking on the challenge of selecting and raising your own (covered below). (Mite “resistance” implies active fighting of the mite; mite “tolerance” includes viral resistance, or other tolerance mechanisms. For the sake of simplicity, I will generally use the term “mite resistant.”) There are a number of beekeepers throughout the world doing exactly this, either formally or informally, many with considerable success, in both small and large operations. There are several researchers in this country doing the tedious grunt work involved in selection, such as Steve Taber, Marla Spivak, John Harbo (retired) and Jeff Harris, Sue Cobey, Latshaw and McAdams, and Tom Rinderer to name a few, as well as dedicated private parties, such as Dan Purvis, Danny Weaver, Kirk Webster, and Joe Waggle (I know I’ve inadvertently left some of you out—these names just came to the top of my head).Funny thing is, when I talk to the large queen producers, mite tolerance is not the main thing buyers are asking for! (The same thing happened years ago when Steve Taber developed a tracheal mite resistant line). Most breeders are selecting for mite tolerance anyway (even if inadvertently), but I’ll tell you, they are going to respond to customer demand. That said, there are few, if any, open-mated stocks that are completely “mite proof,” so producers are hesitant to promise you the moon (and you may be disappointed by those that do!). Also, many beekeepers unfortunately had poor experiences with the first generations of bees touted to be mite resistant. For example, when John Harbo first released the SMR (suppression of mite reproduction) queens, he was clear that they were not intended to be used for production stock. Despite his caveat, a number of beekeepers (myself included) used them as such, and were disappointed by their performance in the field. Through no fault of the SMR queens, some beekeepers are of the “once bitten, twice shy” mentality and are hesitant to try “resistant” stock again.
Another reason for not getting on the bandwagon is, as one of my commercial friends says: Why should I sacrifice five pounds of honey yield by buying mite-resistant stock, when I’m controlling the mite just fine with popsicle sticks dipped into the latest agricultural chemical? Their point is: there is no free lunch, i.e., the bees have their hands full—and if you give them a new job to do, they will have to cut elsewhere. A review by Steve Shepard (2006) considers such tradeoffs of mite resistance vs. honey production. However, in the Big Picture colony stress due to mite damage and miticide residues may well cost the colony more in production than behavioral resistance would. After reviewing yields by mite-resistant colonies vs. Starline bees, Spivak and Reuter (2001) conclude: “colonies bred for hygienic behavior suffer no apparent fitness costs, and perform as well, if not better, than commercial stocks not bred for hygienic behavior…” It doesn’t appear that lack of production is a necessary fault if one makes a point of breeding only from the strongest and most productive colonies.