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No Negative Effect From Extended Exposure To Amitraz

First published in: American Bee Journal, July 2015

No Negative Effect From Extended Exposure To Amitraz

Randy Oliver


First Published in ABJ in July 2015

Why are we hearing of elevated rates of queen loss and poor survivability of colonies these days? Could it have anything to do with sublethal effects of the commonly used miticide amitraz?


Last spring I ran a field trial in order to determine whether treating nucs with Apivar (active ingredient amitraz) strips would affect their buildup. The results (that there was no observable effect) were published in this Journal in October 2014 [1]. But by that time I had further researched amitraz, and was curious as to whether its residues (primarily DMPF) had an adverse effect upon colony or queen health and survival [2]. Since I already had 36 colonies that had been continuously exposed to treatment with Amitraz, I decided to continue the trial to see if there were any long term effects.

Funding sources: I hope to be reimbursed for this trial by a grant from the North Dakota Department of Agriculture, solicited for me by the North Dakota Beekeepers Association.

Materials and Methods

The 36 colonies had been previously started on June 4, 2014, paired by sister queens, with one hive of each pair receiving an Apivar strip on July 1 (which ensured continual release of amitraz, and buildup of DMPF residues in the combs). At the end point of that trial on August 8 there were no significant differences between the Test and Control colonies.

On September 1 &2 the honey flow had ended, but there was still mixed pollen coming in. A few colonies contained beebread, but most were living hand to mouth. All had active broodnests and no sign of nutritional stress. We marked all the queens with paint (Fig. 1), and replaced the existing Apivar strips with new ones to ensure continuous exposure to amitraz. We then fed all colonies equally with pollen sub patties and sugar syrup for the next few weeks.

Figure 1.  Finding all the queens for marking was no fun.  We needed to shake some colonies through a queen excluder “sieve box” to do so.  We lost 2 queens due to injury during the process, and requeened those hives with sister queens.  We breed for “gentle” bees, and can normally work with minimal protective gear.

We also took mite washes of 6 arbitrarily-chosen Control colonies (counts were 2, 3, 4, 0, 2, and 39 per half cup of bees—all save one were at or below a 1% infestation). The single high count was of concern, so we treated all colonies with Hopguard II the next day, and again two weeks later.

Scientific consideration: Managing varroa in the Control colonies was a challenge: the Apivar was controlling varroa in the Test hives, but I couldn’t allow varroa to build in the Controls. Whatever I did to the Controls, I had to also do to the Tests. So I was layering another miticide on top of the amitraz. Therefore I was limited to treatments that wouldn’t be expected to synergize with amitraz—such as Hopguard. Unfortunately, Hopguard is not very effective when colonies contain brood. I had hesitated to use thymol (Apiguard) since there was a report that both it and amitraz might both exert action on the bees’ octopamine receptors [3]. However, a recent study did not find evidence of synergy [4].

On September 29 mite counts were acceptable (below 2% infestation). But due to high mite pressure that we were seeing in our other yards, we treated all hives with ~25g of Apiguard on an index card. The colonies were looking good, but only one colony had brood in the second box of foundation, so we replaced any remaining foundation with recently extracted sticky drawn combs, and fed heavy syrup and swapped honey combs to equalize winter stores. We also fed another pollen patty.

On October 3 mite levels were still below 1%. On November 26 we hit varroa hard with a combination of ~25g of Apiguard plus an oxalic dribble [5]. The colonies were not very strong, averaging about 8 frames of bees. There were no noticeable differences at this time between the test pairs.

On December 22 we fed a pollen sub patty and swapped the Apivar strips for new ones. On January 5 I graded all the colonies for strength, and then fed ½ gal light syrup. On February 5 we moved all live colonies to an almond orchard.

Practical problem: As commercial beekeepers, sometimes beekeeping gets in the way of science. Demand for moving our hives to almonds came early, and things were beyond hectic. At this point in time we misplaced our notes as to which colonies were removed from the trial due to lack of strength. Upon return from almonds we could not locate 5 of the hives (3 Control, 2 Test), so I assumed that they were removed from the trial on Feb. 5.

On March 10 we moved the hives back home, and allowed them to continue to build up on natural nectar and pollen flows. On April 2 I performed the final grading for strength before any of them swarmed.


Upon return from almonds, and at final grading, all colonies were queenright save for one in the Test group. Additionally, the Control colony that had previously had the high mite count had dwindled to only 1.5 frames of bees; I redacted these two colonies from the data set. Although I had planned to check all colonies to confirm that they still contained marked queens, other pressing bee work at that time did not allow me to do so. However, it is unlikely that any of the queens had been superseded since marking them in September, since there are few drones present over winter in this area.

At final grading, the colonies ranged in strength from 8-20 frames of bees. There was no apparent or statistical difference between the groups (Fig. 2).

Figure 2.  Colony strengths over time.  There was no difference in colony strength or survival due to continuous exposure to amitraz.


Despite being continuously exposed to slow-release amitraz (applied as Apivar strips three times over the course of 8 months), we could see no difference in colony buildup, overwintering success, or queen survivability due to treatment. We also found Apivar to be effective at controlling varroa levels.

Although I did not confirm the actual residue levels of amitraz or DMPF in the combs by chemical analysis, previous research [6] suggests that levels would have been substantial, based upon the rate of application versus the numbers of combs covered with bees for most of the duration of the trial.

The results of these two combined trials indicate that treatment with Apivar at the manufacturer’s recommended rate appears to be a safe and effective tool for varroa management.


[1] https://scientificbeekeeping.com/effect-of-amitraz-on-buildup-of-nucs/

[2] https://scientificbeekeeping.com/amitraz-red-flags-or-red-herrings/

[3] Blenau, W, et al (2012) Plant essential oils and formamidines as insecticides/acaricides: what are the molecular targets? Apidologie 43:334–347.

[4] Johnson RM, Dahlgren L, Siegfried BD, Ellis MD (2013) Acaricide, fungicide and drug interactions in honey bees (Apis mellifera). PLoS ONE 8(1): e54092

[5] 5 mL/seam of bees, 3.2% w:v as per https://scientificbeekeeping.com/oxalic-acid-treatment-table/

[6] For references, see https://scientificbeekeeping.com/amitraz-red-flags-or-red-herrings/

Category: Varroa Management
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Effect of Amitraz on Buildup of Nucs

First published in: American Bee Journal, October 2014

Effect of Amitraz on Buildup of Nucs

Randy Oliver

First published in ABJ October 2014

Introduction and Objectives

I was surprised by the slow buildup and lack of drawing of foundation by the nucs in my 2013/14 Pollen Supp Trial. Although the colonies were started during a dearth, due to the near-continual feeding of syrup, I fully expected them to build more rapidly. They didn’t start to build to any extent until shortly after we removed the Apivar strips, but since I had not run a control group without Apivar, I had no way of knowing whether there was any connection.

As I mulled over the question, I came across additional information that furthered my curiosity as to whether amitraz might exhibit negative effects upon colonies (see Amitraz: Red Flags or Red Herrings? in this same issue).

So I decided to run a trial this summer to see whether the application of Apivar strips had a negative effect upon either colony buildup or the drawing of foundation.

Principal Investigator: Randy Oliver, assisted by Eric and Ian Oliver

Funding sources: I hope to be reimbursed for this trial by a grant from the North Dakota Department of Agriculture, solicited for me by the North Dakota Beekeepers Association.

Experimental Design:

  • Set up 36 5-frame nucs with freshly-mated tested queens, of two different maternal lines, equalized for strength, in pairs by queen mother. All hives 10-frame deep singles.
  • Reduce varroa levels to near nil by “natural” miticides known to leave few persistent residues.
  • Randomly assign 1 hive in each pair to receive a single Apivar strip for the duration of the trial (Treatment); open the other hive in each pair but apply no strip (Controls).
  • Add 5 frames of foundation and feed colonies for buildup, adding a second box of foundation to all when the first colony drew out its combs in the first box.
  • Allow colonies to grow, and then grade them for gain in strength and amount of combs drawn.

Trial Log

June 4, 2014 Moved 20 recently-mated queenright nucs to the test yard, which already contained 20 similar nucs from a different queen mother (both Italian mongrels). All nucs oxalic’d at Day 19; all checked for good patterns of worker brood. The nucs were set in pairs, each pair consisting of two nucs headed by sister queens.

June 6 Equalized all into 5-frames in a single. Typically 4 frames with brood.

June 9 Equalized.

June 12 Equalized and treated all with ½ MAQS.

June 19 Checked one hive for mites—4 in ½ cup bee sample–too many.

June 20 Equalized. Treated all with 1 Hopguard II strip.

June 27 Colonies drawing and filling foundation well. Large hive-to-hive variation in the amount of chewed Hopguard paper at the front of hives. Took composite mite samples of ½ cup of bees from 6 pairs of hives. Only 2 mites total in >1800 bees.

June 30 Final equalization of colonies, checked for queenrightness (2 colonies superseding, removed them and 2 others from trial), removed excess frames of bees, leaving each colony with 5 frames of brood, covered solid with bees. Good nectar flow on.

Experimental note: These nucs were considerably stronger than those in the previous trial, since they started with 5 full frames of brood. The experiment also began earlier in the season (July 1 vs. Aug 8), and during a nectar flow rather than a dearth.

July 1 Time Point 0 Good nectar flow on. Overnight, nearly every colony had built several combs underneath the lids (Figs. 1, 2, and 3).

Figure 1.  All colonies were vigorously drawing comb on a natural nectar flow and ready to rock and roll.  Remains of Hopguard II strip visible.

Figure 2.  Colonies were in pairs, each pair headed by sister queens.  We flipped a coin to decide which of each pair received an Apivar strip, and inserted one strip near the center of each treated hive.  Here’s Ian adding the frames of wax-coated plastic foundation to the 5-frame nucs.

Figure 3.  Start of trial, treatment randomly assigned to each pair.  I would have preferred a less-crowded test yard, but this one was near home.

July 7 Spot checked. Some colonies drawing foundation, nectar flow tapering off. Fed each colony ½ gal of 1:1 sucrose syrup.

July 21 All colonies appeared strong and building. The strongest had all 10 frames drawn and were heavy; the weakest had not yet drawn all 10 frames, nor covered them. The main flow is tapering off. Fed ½ gal 1:1 sucrose syrup. Added deep super of foundation to each colony.

Experimental note: the strong nectar flow after the start of the trial was unexpected, based upon the previous history of this yard.

July 24 Fed ½ gal 1:1 sucrose syrup.

Aug 8 Time Point 1 Main flow appears to be over, but still mixed pollens coming in. Since there were large differences in strength, we decided to perform the end point assessment. Graded all colonies (by Randy) in morning (by 9:15), blinded as to treatment.  Graded for seams of bees and number of well/drawn combs of foundation (out of possible 15).


The final grading took place at Day 38. The Control colonies averaged 8.8 (SEM 0.3) seams of bees; the Apivar-treated colonies averaged 8.5 (0.3). There was no significant difference between the two (Mann-Whitney p = 0.61), as reflected in the histogram of colony strengths in Fig. 4.

Figure 4.  There was no apparent difference in buildup due to treatment with Apivar.

There was no difference between groups in the number of combs of foundation drawn– 5.9 (SEM 0.6) in the Controls; 5.7 (0.5) in the Apivar-treated group.


The application of one Apivar strip to a strong 5-frame nuc on a decent nectar flow did not appear to inhibit either colony buildup or the drawing of foundation. I am toying with continuing this trial, periodically replacing the Apivar strips, through next spring, to see whether there are any other observable effects upon the colonies.


Thanks to Bonnie and Brent Woodworth and the North Dakota Beekeepers Association for their support of my research.

Category: Pesticide Issues
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