Apivar (Amitraz) for Varroa: Application Guide and Resistance Tracking

Amitraz resistance is emerging in US varroa populations. That sentence should be in every beekeeper's head every time they reach for a box of Apivar strips.

Apivar has been the workhorse of commercial varroa management for good reason, it's highly effective, relatively easy to apply, and works during active brood season when other treatments have limitations. But it only stays highly effective if you use it correctly and rotate off it before resistance takes hold in your apiary.

Here's how to apply Apivar correctly, how to monitor for declining efficacy, and how to know when it's time to rotate.

TL;DR

Place Apivar strips in the brood nest between frames, not in the honey super
Use 1 strip per 5 frames of bees; do not underdose as this accelerates resistance development
Leave strips in for the full 42 days; removing early reduces efficacy and contributes to resistance
Remove strips before adding honey supers; check your state's PHI requirements
Calculate pre- and post-treatment mite counts to verify the treatment worked as expected
VarroaVault tracks your Apivar application history and flags when efficacy drops below 90%

What Apivar Is and How It Works

Apivar strips contain amitraz, an insecticide that acts on the octopamine receptor in varroa mites, causing neurological disruption and death. Bees have different receptor chemistry and are largely unaffected at label doses.

Each strip is impregnated with 500mg of amitraz. When placed between frames where bees travel, bees contact the strip and transfer the active ingredient throughout the colony via normal grooming behavior. This "walk-through" exposure mechanism requires good bee-strip contact for the full treatment window.

The treatment window is 42 days minimum. This isn't arbitrary, the 42-day window is designed to cover two full varroa reproductive cycles, ensuring mites that were in capped brood during the first application emerge and are killed before the treatment ends.

Step 1: Confirm Timing, No Honey Supers

Apivar cannot be used when honey supers are on the hive. Amitraz is not approved for use during honey production periods. Remove all supers before application.

This means Apivar is typically applied:

Post-nectar flow (late July through September) in most US regions, the critical late-summer window before winter
Early spring before supers go on, if spring mite loads require treatment

The late-summer window is more important for most beekeepers. Getting below the 1% mite threshold before the colony raises its overwintering bees (August-September) is the goal.

Step 2: Check Your Pre-Treatment Mite Count

Don't apply Apivar without a baseline count. HiveTracks has no amitraz resistance flag or rotation reminder, you need to know your starting mite load so you can calculate efficacy after treatment.

Do an alcohol wash on each hive (or a representative sample from each yard). Record:

Date of count
Hive identifier
Mite count and infestation percentage

This becomes your pre-treatment baseline. Without it, you'll never know if the treatment worked.

Step 3: Apply Strips Correctly

Strip count by colony size:

1 box colony (single deep or equivalent): 1 strip
2-box colony: 2 strips
Very large colonies (3 or more boxes): 2 strips is still the standard; some beekeepers use additional strips in extreme cases but always follow label guidance

Placement: Insert strips vertically between frames in the brood nest, toward the center of the cluster. One strip should be in the first 1/3 of the brood nest, the other in the last 1/3 (for two-strip applications). Bees must be able to walk on both sides of the strip.

Poor placement is one of the most common reasons for low efficacy. Strips tucked into corners away from the cluster, or inserted horizontally, make poor bee contact.

Record the application date. This determines when you remove them.

Step 4: Leave Strips in for the Full 42 Days

The 42-day minimum is non-negotiable. Removing strips early, even at day 35, leaves the second reproductive cycle partially uncovered. Mites that were in capped brood during weeks 1-3 are emerging in weeks 5-6. They need to encounter the strip after emergence.

Maximum duration: Don't leave strips in past 56 days (8 weeks). Extended exposure contributes to residue buildup and, critically, to resistance selection, since low-dose continued exposure is worse than full-dose treatment.

If you have honey supers ready to go, wait. 42 days is six weeks. Plan your treatment timing so removal happens at least 2 weeks before you want to add supers.

Step 5: Post-Treatment Count and Efficacy Scoring

Remove strips on or after day 42. Wait 7-14 days, then do a post-treatment alcohol wash.

Calculate efficacy:

((Pre-count − Post-count) / Pre-count) × 100

Target: 90%+ efficacy, with post-treatment mite load below 1%.

If your efficacy is below 90%:

Check application, were strips in the brood nest with good bee contact?
Was treatment duration the full 42 days?
Were temperatures appropriate? Amitraz becomes less effective at low temperatures.
If all application factors were correct, suspect amitraz resistance.

How to Detect Amitraz Resistance

Amitraz-resistant varroa strains have been detected in multiple US states as of 2025. Resistance doesn't appear overnight, it develops through repeated selection pressure from amitraz exposure. Signs of developing resistance:

Declining efficacy over treatment cycles. If Apivar used to give you 95% efficacy and now gives 65%, that's resistance developing.

Post-treatment counts that don't drop to expected levels. Pre-count of 5%, post-count of 3% = 40% efficacy. That's a failure, not a mediocre success.

Recovery of mite loads faster than reinfestation can explain. If your mite load returns to 2% within 6 weeks of a "complete" treatment and you're not near other apiaries, something survived the treatment.

VarroaVault cross-references your efficacy scores across treatment cycles and flags when a pattern of declining amitraz efficacy emerges, before you've lost colonies to a failed treatment season.

When to Rotate Off Amitraz

If you've used Apivar for your fall treatment two years in a row, rotate it out for at least one full cycle (one year, spring and fall). Rotation to organic acids (OA, formic) or thymol breaks any resistance selection pressure.

If efficacy drops below 90% at any point, rotate immediately. Don't run a second consecutive Apivar treatment hoping for better results.

FAQ

How long do Apivar strips need to stay in the hive?

42 days minimum. This is the treatment window required to expose mites emerging from two full cycles of capped brood. Removing early leaves late-emerging mites unexposed and reduces overall efficacy. Don't exceed 56 days. VarroaVault tracks your application date and alerts you on day 42.

Can I use Apivar while honey supers are on?

No. Apivar is not approved for use during honey production periods. Remove all honey supers before application. This is why late-summer timing is standard, supers are typically removed after the main nectar flow, before fall prep. If you need to treat during flow, consider MAQS (formic acid), which has a honey-super-on label.

How do I know if my hive has amitraz resistance?

Calculate your treatment efficacy score using pre and post counts. If a correctly applied 42-day Apivar treatment gives you less than 90% reduction in mite load, amitraz resistance is likely. Compare efficacy scores across years, a trend from 95% to 80% to 65% over three seasons is a clear resistance signal. VarroaVault's amitraz resistance tracking flags these patterns automatically and recommends rotation timing.

How do I know if my varroa treatment is working?

Run a mite count 2-4 weeks after the treatment ends and compare it to your pre-treatment count. The efficacy formula is: ((pre-count - post-count) / pre-count) x 100. A result above 90% indicates effective treatment. Results below 80% should trigger investigation for possible resistance, application error, or reinfestation. Log both counts in VarroaVault to track efficacy trends across treatment cycles.

How often should I check mite levels in my hives?

At minimum, once per month (every 3-4 weeks) during the active season. Increase to every 2 weeks when counts are near threshold or after a treatment to verify it worked. In fall, monitoring frequency matters most because the window to treat before winter bees are raised is narrow. VarroaVault's monitoring reminders can be set to your preferred interval for each apiary.

What records should I keep for varroa management?

Each record should include: date of count or treatment, hive identifier, monitoring method used, number of bees sampled, mites counted, infestation percentage, treatment product name and EPA registration number, dose applied, treatment start and end dates, and PHI end date. State apiarists typically expect this level of detail during inspections. VarroaVault captures all of these fields in a single log entry.

Sources

American Beekeeping Federation (ABF)
USDA ARS Bee Research Laboratory
Honey Bee Health Coalition
Penn State Extension Apiculture Program
Project Apis m.

Don't Skip the Post-Count

Apivar is still one of the best tools available when it works. But "when it works" is the key phrase. Track your efficacy. Rotate when needed. Start logging in VarroaVault and know, with data, whether your treatment is doing its job.

Get Started with VarroaVault

Amitraz (Apivar) is one of the most effective varroa treatments available when applied correctly and monitored for efficacy. VarroaVault logs your treatment dates, calculates efficacy from your pre/post counts, and alerts you when results suggest rotation is needed. Start your free trial at varroavault.com.