Impact of OAV at the Rearing of Brood
Ernie Daley and Randy Oliver
First printed in ABJ June 2024
I’ve used OAV (oxalic acid vaporization) for varroa keep watch over for over ten years and feature puzzled whether or not (1) the remedy may well be carried out proactively previous to the advent of package deal bees, and (2) whether or not the remedy would adversely have an effect on the improvement and survival of larvae. So, with steering through Randy Oliver, I ran a few experiments.
SET UP OF EXPERIMENT #1
I puzzled whether or not I may follow oxalic acid vaporization to drawn combs (as a proactive “residual insecticide floor remedy”) to keep watch over varroa, carried out before you install the bees. My first query was once whether or not this sort of remedy would have an effect on the primary spherical of brood laid through the queen (most likely because of oxalic crystals within the cells). To reply to that query, Randy advised that I run a take a look at through masking part of a body of empty brood cells with plastic wrap (to supply a Keep watch over team unexposed to OA) after which reveal the brush to oxalic acid vaporization. Then afterwards take away the plastic wrap and go back the handled comb to the hive for the queen to put eggs in.
So, in past due Might I ran two replicates of the take a look at, making ready the combs (Determine 1), then striking every of them within the heart of a bee-free hive consisting of a medium tremendous with empty drawn combs on both sides, after which making use of 2 grams of OA through vaporization (Determine 2).
Fig. 1 Two frames of empty drawn comb, part wrapped with plastic wrap to supply each a handled Check and an untreated Keep watch over team on every comb.
Fig. 2 I used a 110 Volt OA vaporizer to warmth two grams of oxalic acid to 315°F to vaporize and disperse it right into a medium tremendous containing 10 drawn frames (with out bees) with the 2 Check frames within the heart of the field, by way of a hollow within the flooring rim.
Ten mins after making use of the OAV, I peeled the plastic wraps off the Check combs, and positioned them into particular person excluder cages, which I then inserted again into the facilities in their hives. I then offered a 3-lb package deal of bees (containing their mom queens, caged for delivery) into every hive, after first liberating and confining their queens onto their respective Check combs (Figures 3 &4).
Fig. 3Freeing the caged queen from the package deal into the excluder cage through which she will likely be confined.
Fig. 4 The excluder cages (with queens) returned to their colonies.
RESULTS OF EXPERIMENT #1
3 days after confining the queens, I got rid of the Check frames from the excluder cages, and staring at that a lot of eggs were laid, returned them (uncaged) to their respective colonies. Six days later I noticed larvae and capped brood on each Check frames (Determine 5 and six). There was once no noticeable distinction within the brood patterns of the OAV and Keep watch over halves of the Check frames in both colony.
Fig. 5 Check body from colony “A” 9 days after pretreatment with OAV appearing brood construction on each the Keep watch over and OAV halves.
Fig. 6 Check body from colony “B” 9 days after pretreatment with OAV appearing brood construction on each the Keep watch over and OAV halves.
EXPERIMENT #2
Now that I had made up our minds that OA pretreatment didn’t adversely have an effect on the survival of eggs or newly emerged larvae, I used to be in a position to check whether or not remedy of combs with eggs and rising larvae already provide would have an effect on their survival or construction.
To reply to this query, Randy advised that I repeat the primary take a look at, however this time with eggs and larvae already provide once I carried out OAV to the combs.
Operating in early July I once more used an excluder cage to restrict a queen on a body of drawn comb for 6 days. Once I returned six days after confining the queen, I noticed eggs and larvae on either side of the body. I then wrapped part of the Check body with plastic wrap (Determine 7) and returned it to the hive with out the excluder cage.
Fig. 7 The Check body with eggs and larvae 6 days after confining the queen onto the brush, previous to making use of OAV. One part is wrapped with plastic wrap to supply a Keep watch over team unexposed to OA.
I then carried out two grams of oxalic acid through vaporization to the double-medium colony (the standard dosage I’d follow when treating a double medium for varroa). Ten mins after finishing the OAV, I got rid of the Check body from the hive, peeled off the plastic wrap, and returned it to the colony for 11 days. The ages of the eggs and larvae previous to OA vaporization have been 1-6 days.
RESULTS OF REPLICATE #1
11 days after the OAV software, I got rid of the Check body and inspected either side for brood survival. There was once no noticeable distinction in brood survival or construction between the OA-exposed and Keep watch over halves of the Check body (Figures 8 and 9).
Fig. 8 Aspect some of the Check body 11 days after OAV, appearing brood construction on each the Keep watch over and OAV halves.
Fig. 9 Aspect two of the Check body 11 days after OAV, appearing brood construction on each the Keep watch over and OAV halves.
Mirror #2
At Randy’s advice, I replicated the experiment with more youthful eggs and larvae, to peer whether or not I’d get similar effects. I ran this mirror initially of August, the use of the similar double-medium hive. By way of now the colony had expanded and bees coated fourteen of the twenty frames. I confined the queen as ahead of for 4 days. Once I returned 4 days after confining the queen, I noticed the queen laying (Determine 10) and eggs (Determine 11) and larvae on either side of the body.
Fig. 10 The queen laying an egg at the Check body at the fourth day of confinement after removing from the excluder cage.
Fig. 11 Eggs and larvae noticed at the Check body 4 days after confining the queen.
As ahead of, I wrapped part of the Check body with plastic wrap and returned it to the hive. I then carried out two grams of OAV, and after ten mins unwrapped the plastic from the Keep watch over facet and returned the Check body to the colony for 13 days. The age of eggs and larvae previous to OAV remedy was once 1-4 days.
RESULTS OF REPLICATE #2
Once I returned 13 days after OAV software, I got rid of the Check body and inspected either side. Each the OAV and Keep watch over halves had an identical brood patterns and not using a observable distinction in construction or survival (Figures 12 and 13).
Fig. 12 Aspect some of the Check body 13 days after OAV appearing brood construction on each the Keep watch over and OAV halves.
Fig. 13 Aspect two of the Check body 13 days after OAV appearing brood construction on each the Keep watch over and OAV halves.
DISCUSSION
So far as I may inform there have been no opposed results at the construction of eggs or larvae whether or not brood frames were pretreated with OAV previous to egg laying, or if OAV was once carried out when eggs and larvae have been already provide. The volume of brood, the development, and the improvement at the OAV part of the body gave the impression to be the similar as that of the Keep watch over part in each experiments.
OXALIC RESIDUES FOLLOW UP IN CALIFORNIA (through Randy)
Following the sector experiments through Ernie, I used to be curious as to how a lot oxalic acid in truth remained in every cellular after Ernie carried out his vaporizations (with out or containing larvae). I calculated how a lot overall floor house there may be in a medium tremendous of drawn combs (together with the woodenware (best, backside, and aspects) and ten frames (tops, bottoms, ends, and faces of combs): it labored out to 3736 sq. inches. Dividing 2 grams of oxalic acid through that house, I were given a theoretical results of 535 micrograms (µg) in line with sq. inch of floor house (83 µg pr cm2), or 23 µg in line with cellular face.
Notice on titrations: I’ve finished intensive paintings (as but unpublished) on quantifying the quantities of oxalic acid on bees’ our bodies after remedy with oxalic acid carried out through other strategies. Since titration doesn’t establish the real form of acid, my microgram values are for “OA equivalents.”
The theoretical dose from the registered software strategies is ~100 µg in line with bee, however that quantity is seldom completed within the box. A real dose of ~30 µg in line with bee will kill mites. An grownup bee can maintain 200 µg of oxalic acid carried out as a dribble, however the theoretical 23 µg in line with cellular face will have the possible to have an effect on a newly-emerged larva.
So in conjunction with my helpers Rose Pasetes and Corrine Jones, we ran six separate checks on other days, every time making use of 2 grams of oxalic acid through vaporization (the use of a ProVap 110) to other deep supers (since I didn’t have any mediums) of empty drawn brood comb (for which there can be theoretical residues of 17 micrograms in line with cellular face). We first showed that there have been no preexisting acid residues within the cells through the use of a pipette and indicator answer.
Run 1, with plastic squares at the comb faces
For our first run, we additionally pressed 1 cm2 items of plastic (reduce from a deli container) into the brush surfaces to quantify the quantity of residues at the comb floor to match to the residues inside of the cells.
After permitting a part hour for the OA vapor to settle, we got rid of the handled combs and once more used a pipette to check haphazardly-chosen cells for acid residues (measured in OA equivalents) (Determine 14).
Fig. 14 We dropped 5 drops of indicator answer into every cellular to check, then sucked it again out with a pipette. Right here, in a convention run, Rose has positioned a Keep watch over drop within the heart, and drops from examined cells round it. The indicator dye turns inexperienced after which orange relative to the quantity of acid residues. To our wonder, there have been simplest 1-2 micrograms of OA equivalents in line with cellular, and simplest 0-10 µg in line with cm2 at the plastic take a look at squares –– a long way lower than the predicted 83 µg!
Out of interest, I scooped some beebread out of 3 cells, figuring out that bees use lactobacilli to maintain pollen with lactic acid. The scoops of beebread titrated at 450, 360, and 860 µg OA equivalents of acidity! Even supposing lactic acid isn’t rather as reactive as is oxalic, it is helping to provide an explanation for how bees can tolerate remedy with OA.
Anyway, the low quantities within the cells and at the plastic stunned us, and after we later lifted the handled field, we spotted {that a} portion of the OA had crystallized on the front the place the move of vapor hit the ground board (Determine 15).
Fig. 15 This pile of OA crystals amounted to just a fraction of a gram, however presentations that it is crucial for someone making use of OAV to make certain that the move of vapor does indirectly hit anything else throughout the hive!
So we ran 5 extra experiments:
Run 2, with useless bees pinned to the combs
In Run 2 we pinned useless bees at the combs (Determine 16) to match the quantity of OA that accrued on every bee to the quantity that we’d prior to now discovered after we titrated bees from clusters after OAV remedy (there may be most often ~10 µg in line with bee in a while after software).
Fig. 16 We pinned useless bees to the combs to peer how a lot OA caught to them versus the plastic squares used within the first run. See Fig. 17 for the effects.
Fig. 17 The reference tube it to the left. Maximum bees had lower than 5 micrograms, however the yellow one examined at 60. There was once sudden variation, in spite of all of them having been positioned between central combs neatly above the vapor move. Once more we titrated minuscule ranges of OA within the cells.
Run 3, with a handful of reside bees unfastened at the combs.
So I determined to place a handful of younger reside bees unfastened at the ten combs of a special tremendous. I plucked off a batch of them ten mins after OAV software (Determine 18), after which ten extra when they had walked at the combs for an hour (Determine 19).
Fig. 18 At 10 mins publish software, maximum bees exhibited simplest slight quantities of acidity, despite the fact that a couple of titrated at 40-50 microgram equivalents. Once more, unusually large variation for a remedy carried out as a fog.
Fig. 19 However through an hour, the entire bees had picked up a lot more oxalic acid, possibly from strolling over the handled comb surfaces.
Run 4, with a tiny cluster of reside bees
Nonetheless intrigued through our findings, we went out to a stack of just lately brought-home deadout supers to search for a cluster of useless bees to check, and to my wonder discovered a hand-sized cluster of reside bees with a queen between the higher parts of 2 combs. So we positioned that field between a backside board and canopy, and carried out 2 grams of OAV (Figures 20- 24).
Fig. 20 Once we got rid of the quilt after 10 mins, shall we instantly see that the bees had a “dusting” of white oxalic microcrystals on their setae (“hairs”).
Fig. 21 The bees have been way more “frosty” taking a look than after a regular vaporization.
Fig. 22 A detailed up of an ordinary bee from the former photograph coated with oxalic acid crystals ‑‑ way over I see once I OAV a full-sized cluster! I hesitated to titrate them…
Fig. 23 I simplest titrated the primary 3 bees, because it took such a lot of drops of titrant. Their OA equivalents have been 630, 1330, and 150 micrograms! I do not know as to why this tiny cluster of bees were given hit so closely through precisely the similar vaporization that we’d been giving for the opposite take a look at runs.
Fig. 24 The cells additionally contained way more acidity than within the different runs: starting from 5 to twenty micrograms. Cross determine!
Intrigued once more, we carried out but any other experiment.
Run 5, reside bees in push-in cages
This time I positioned a couple of reside bees into every of a number of push-in cages (large Mason jar lids with 1/8” display), situated between other combs, close to the highest, and once more carried out the same quantity of OAV by way of the doorway. The consequences are proven in Determine 25 and Desk 1.
Desk 1 The acid residues at the bees have been upper than the ones for Runs 2 and three, however a long way lower than the ones in Run 4.
Fig. 25 Regardless of the relatively-high quantities of acid at the caged bees, the quantities of residues within the cells have been once more slightly detectable (reference drops beneath, take a look at drops from the combs above).
Conclusions
To our nice wonder, within the 5 experimental runs –– the use of the similar vaporizer at the similar stand, with nearly-identical bins of combs –– there have been huge variations within the quantities of acid residues on bees at the combs, and throughout the cells. The quantities of acid at the bees was once normally way more that I practice once I’ve titrated complete hives (most commonly 8-10 body clusters). So I’m no longer stunned that Ernie didn’t practice any opposed results from OAV upon eggs or larvae.
Experiment 6, Are living bees offered after vaporization
At this level of time, I noticed that we hadn’t but addressed Ernie’s first goal –– to resolve whether or not he may preload bins of drawn comb with oxalic acid through vaporization, before you install a package deal of bees, for the aim of killing mites at the offered package deal bees. This was once primarily based upon the belief that the acid residues at the combs would switch to the bees. The result of Run 3 without a doubt indicated that they might.
So we ran but any other experiment. We once more arrange a field of acid-free drawn brood combs and vaporized it with 2 grams of oxalic, then allowed it to take a seat for an hour for the entire acid to settle. We then shook bees from an untreated colony, and showed through titration that they have been freed from acidity. We allowed any older bees to fly off to make certain that after we offered them onto the handled combs, that they might stay within the new “hive.” We offered a cupful of the possibly younger bees, changed the hive duvet, and permitting them to stay within the “hive,” freely strolling at the combs. We took samples of them after 10 mins, 1 hour, and two hours (in which time their acid ranges ceased expanding (Desk 2).
Desk 2. Equivalent as in Run 3, the acid ranges of the bees greater all the way through the primary hour, after which stabilized. Our discovering: Bees can readily “select up” an excessive amount of OA microcrystals through strolling over handled combs for an hour.
Experiment 7, to be finished
The acid ranges at the bees above can be masses to kill mites –– only if the acid crystals have been allotted over the bees’ our bodies. However in a previous initial experiment I had discovered that acid residues of this stage, when simplest at the bees’ ft, didn’t motive any varroa mortality in an incubator trial. Sadly, through this time it was once already November and my dang sons had already handled any hive with measurable mites, so we want to wait till subsequent season to check Ernie’s assumption –– which we’ll do through evaluating mite drops on stickyboards after introducing high-mite programs to bins of handled or untreated combs. If someone desires to sign up for us in acting this experiment, we’d love to peer your effects!
ACKNOWLEDGEMENTS
I need to thank Randy Oliver for his mentorship, help in experimental design, and the writing of this newsletter. And we thank Rose and Corrine for his or her assist with the entire titration experiments.