Varroa by the Numbers: Testing Before Treating

You cannot manage what you have not counted. A colony that looks strong in July with an unmeasured mite load is the classic Similkameen dead-out in February — bees gone, stores full, a story that repeats every year in yards that never picked up an alcohol wash jar. Varroa destructor is not an occasional pest here; it is a permanent resident of every colony in this valley, and the only question worth asking is how many are riding on your bees today, this month, this apiary.

I have watched more colonies die from mite-vectored viruses than from starvation, cold, or every other cause combined. Deformed wing virus, acute bee paralysis virus, and a dozen other RNA viruses use the mite as a hypodermic needle, injecting virus straight into the fat body and hemolymph every time a mite feeds. By the time you see visibly deformed wings on adult bees, the colony has already crossed a viral threshold that no autumn treatment will reverse in time. Counting mites in July is how you buy back the fix.

Why an alcohol wash and not a visual guess

Beekeepers have tried nearly everything to avoid killing three hundred bees to answer this question — sticky boards, natural mite drop counts, sugar shakes, even simply watching bees on the landing board for signs of stress. None of them come close to the accuracy of an alcohol wash, and in an operation of any size the half-cup of bees you sacrifice is cheaper than the colony you lose to an unmeasured load. This is not a hobby-versus-commercial distinction. It is a discipline distinction.

Running the wash

1. 1Choose a frame of open brood near the centre of the nest — young nurse bees carry the heaviest phoretic mite loads and give you the truest picture.
2. 2Shake the bees from that frame into a wide plastic tub, confirm the queen is not among them, then scoop roughly 300 bees (about half a cup, or 1/2 a standard measuring cup levelled) into a wash jar or dedicated mite-check cup with a mesh basket.
3. 3Cover the bees with windshield-washer fluid or 70% isopropyl alcohol — enough to fully submerge them.
4. 4Shake vigorously for a full 60 seconds by the clock. Under-shaking is the single biggest source of a falsely low count.
5. 5Pour the alcohol through the mesh into a white tray or lid. Count every mite that separates from the bees.
6. 6Divide the mite count by three to get mites per hundred bees — the number you will log and compare month to month.

Reading the number: monthly thresholds

A mite count means nothing without context. Three mites per hundred in April, with a full brood-rearing season still ahead, is an emergency. The same three per hundred in late August, heading into a broodless window and an oxalic treatment, is manageable if you act promptly. The table below is the threshold set we use across our yards, adjusted for the shorter, more intense Similkameen brood season compared to coastal or prairie operations.

Notice that the threshold tightens again in September. A colony can carry a moderate mite load through the honey flow and still produce a crop, but the mites you tolerate in July are producing the virus-laden winter bees you will lose in January. September is not the month to relax; it is the month the whole year's tolerance gets called in.

Treatment options: mode of action, temperature and honey supers

Every registered varroacide works by a different mechanism, and every mechanism has a temperature window and a honey-super restriction attached to its Canadian label. Read the label on the product in your hand every single season — formulations and directions change, and Health Canada's Pest Management Regulatory Agency (PMRA) registration is the only legal authority for use, not habit or what your neighbour did last year.

Rotation: mode of action, not brand

• Never apply the same active ingredient twice in successive treatment rounds within a season — mites under selection pressure from a single mode of action develop resistance within a handful of generations.
• A typical Similkameen rotation: formic acid in the two to three weeks after pulling honey supers (still warm enough, brood present so it hits phoretic and capped mites together), thymol in the cooler shoulder weeks of early autumn if a second treatment is needed, then oxalic acid vaporization in the broodless window of late October to November as the season-closing treatment.
• Amitraz (Apivar) is a longer-duration strip treatment, typically 42 to 56 days in the colony — plan its placement around honey-flow timing since it cannot overlap with supers.
• Track every treatment applied per colony, per yard, with date, product, and dose in your record system. Resistance shows up first as a rotation you cannot remember properly.

Mechanical and cultural assists

Chemical treatment is the backbone of varroa IPM, but it is not the whole structure. Drone brood removal exploits the mite's own preference: varroa reproduce roughly 3.5 times more successfully in drone cells than in worker cells because of the longer drone development period. A frame of drone foundation placed at the edge of the brood nest, allowed to be capped, then removed and frozen or destroyed before emergence, pulls a meaningful fraction of the season's mite reproduction out of the colony without a single chemical input. Run it every 24 days through the brood season and it becomes a real contributor, not a token gesture.

Screened bottom boards drop a small percentage of phoretic mites out of the hive permanently and improve ventilation, but treat their contribution as marginal — five to ten percent reduction at best. They are a good habit, not a strategy.

Level-specific practice

“The bees that need the least help from you are the ones worth keeping. Everything else is a science project with a honey crop attached.”

Breeding out of the problem

Chemical rotation buys time. Genetics is the only long-term answer. Varroa Sensitive Hygiene (VSH) behaviour — where workers detect and remove mite-infested pupae before the mite completes reproduction — is heritable, measurable, and improvable within a closed breeding population over a handful of seasons. Record mite counts by queen line at every wash. When you requeen or graft for next year's queen cells, favour breeder colonies that have consistently shown counts at or below threshold across a full season without treatment intervention, not just colonies with a big honey crop.

None of this replaces testing. Genetics reduce your mite pressure over years; the alcohol wash tells you what is happening in the colony in front of you today. Run both, log both, and treat the jar of alcohol and the queen-line spreadsheet as two halves of the same tool.