Queen Losses Reduced
to Normal Levels Using 50% Formic Acid With Essential Oils
We found that using higher concentrations of formic acid in varroa mite treatments
increased queen losses, apparently due to a possible disruption of the worker's
normal pheromone communication. Because of this disruption, they recognize
her as an intruder and ball (kill) her. Also, higher concentrations of formic
acid may have an adverse effect on less resilient, older queens, resulting
in their loss. We have determined that, after adding Honey-B-Healthy·
(HBH), which contains a special balance of certain essential oils, to the
formic acid mix queen losses returned to normal, about 5% or lower. [1]
Our October, 2006 trial in Florida showed a loss of two queens out of 20 colonies
treated with a 50% formic acid dose with 15ml HBH. Each colony had two full
depth brood chambers. This dose may have been too strong causing an inordinate
number of bees to leave some of the colonies. We now believe that a dose of
100ml 50% formic immediately mixed with 15ml HBH may have been better at treating
the mites with a lower queen loss by not causing the bees to exit the colony
during the application. Normal queen loss is 5% or less in control colonies[1].
One lost queen out of 20 is acceptable when you consider the high efficacy
of 93.5 % of varroa mites killed in sealed drone cells. Our two queen loss
may have been due to other factors such as alcohol washes, colony manipulation
before, during, and after treatments.
Our August trial in Florida had no queen losses. A 39 colony trial in Cumberland, MD during August and September, 2006 were used as test colonies prior to the Florida trials, and had one queen lost in a colony that received a high dose in high temperatures. Additionally, many bees streamed from the entrance and a high amount of open brood and newly hatching bees were killed as well. Other colonies of the 39 treated received a lower but efficacious dose. At these hives we noted agitated bees at the entrance but no bees running out. There appears to be a fine line for these treatments with possibly a 10ml swing either way sometimes showing major differences in bee behavior and lost queens. A good indicator appears to be the activity of the bees at the colony entrance. If the dose is too high the bees will run out the entrance within a few minutes; if it is too low, the bees will not be hampered at all by the treatment. We are noting that both agitated bees as well as bees displaying reluctance to enter the colony are good indicators that a proper dose has been administered. After 24 hours, when the fumigator is removed, a handful of dead workers in front of the hive is also a sign of an adequate treatment.
Our most recent trial on 2-3 January, 2007, in Rockledge,
Florida, showed one queen lost in the 20 colony single story trial using 90ml
of 50% formic acid and 15ml HBH with about a 95% + kill of mites in the cells.
This 5% queen loss is within the normal range of queen losses in control colonies
[1].
The 20 treatment colonies showed 58 mites in the alcohol washes of 400 to
500 bees per colony (for 20 colonies) washed one week after the treatment.
Some of these 58 varroa (ca. 50%) may have been mites killed the week before
and still stuck under the bee's sternites. They may have been drifting or
lost bees leaving infested or collapsing colonies nearby. The 10 controls
had 247 mites on the 400 - 500 washed bees per colony, nearly ten times as
many mites. An email message from our collaborator, David Webb, one week after
the 2 January treatment: "I noticed when I did the washes that a few
mites floated in the alcohol; I figured they were dead and dried, in one wash
two out of four floated. Sugar rolls may show us if this is the case."
Trials in Cumberland Md. over the past 5 years have shown that a 93% + kill
of varroa in the cells means a nearly100% kill of mites on the bees. The alcohol
washes in the controls showed 0.0494 mites per bee as compared to the treatment
colonies of 0.0058 per bee, with the controls having roughly 10 times more
mites on the bees than the treatment colonies
Over the past five years we measured the temperature of the air coming out
of the entrance and it was nearly always 90°F (32.2°C). We get excellent
mite kill on most colonies (93% or more in 16-20 hours in the drone cells
with an even higher kill in worker cells). We see very little interruption
of queen performance, and a balled queen reduction from 25% (without HBH)
to 5% (with HBH). In early experiments we conducted similar trials with formic
acid only (no HBH) at the same concentration and amount and lost several queens
(one out of four or 25%). Queen losses were reduced to one out of twenty or
to 5% loss using the HBH-FA mix. This is within the norm for queen losses
in control colonies. [1]
Working up to our present treatment, one of our early treatments to eliminate
queen loss was by caging the queen and placing her above the fumigator during
the treatment period. Still another attempt involved spraying exposed bees
on and between exposed brood supers along with the entrance with HBH sugar
water spray (4 tsp. per quart). This, along with adding HBH to the 50% formic
practically eliminated queen losses. Both of these methods to, while proving
effective in preventing queen loss, were impractical for commercial beekeepers.
We find that adding Honey-B-Healthy· to the formic acid at the time
of application has the same affect.
The following studies have shown increased queen loss using high concentrations
of formic acid:
- Department of Entomology, University of Manitoba, Winnipeg MB R3T 2N2, Canada
showed the highest concentration of formic treatment used in their study killed
33.3% of queens compared with 4.8% loss in the control. [1]
- Queen loss seems to occur more frequently with the use of higher concentrations
of formic acid (e.g., 85%), under the following conditions: hot weather; when
older queens are present; or when bees are not able to escape pockets of concentrated
fumes.[2]
- Queen losses were a severe problem at the beginning of FA treatments but
have been significantly reduced to exceptional cases by correct use of modern
application methods. Damage to open brood and hatching young bees, however,
cannot be completely excluded. Damage rates depend on ambient temperature
and the distance between the evaporation device and the brood. Under mid-European
conditions, a moderate loss of brood has no negative effect on colony over
wintering [3].
Summary: Our research over the past 6 years using our formic acid protocol
with the addition of essential oils has reduced queen loss from 25% or more
down to 5% or less, and we kill 93.5% of the varroa
mites in capped drone cells.
[1]
Underwood RM, Currie RW. 2004. Indoor winter fumigation of Apis
mellifera (Hymenoptera: Apidae)
colonies infested with Varroa destructor (Acari: Varroidae) with formic acid
is a potential control alternative in northern climates. J. Econom. Entomol. 97(2): 177-186.
[2]
Anonymous. 2004. Proposed Regulatory Decision Document. PRDD2004-05.
Formic Acid/NOD Formic Acid Pad and Mite-AwayII©
Formic Acid Pad.
[3]
Imdorf1, A., Jean-Daniel Charrière1 & Peter Rosenkranz2 1999. Varroa Control
with Formic Acid. A web page In: "Coordination
in
