Oxalic Acid Vapor (OAV) Mite treatments must address two issues:
1) the mite infestation (mites produced by your own hive)
2) the mite importation (mites brought into the hive via robbing from dying mite bombs)
The Quick Answer:
Mites spend about 5 days in a “phoretic stage” riding/feeding on bees before jumping back into a brood cell to procreate.
Oxalic Acid does not kill mites in capped brood. So, any mite that emerged from under capped brood after your last treatment will be killed if you treat every 4 days.
A mite in a cell that was just capped on the day of your first treatment emerges 14 days later (it it jumped into a drone cell). So your treatments must cover at least 14 days or 5 treatments.
The 5x4 treatment plan:
1) Treatment Plan and Mite Stages
Day 0: Treatment 1 kills all phoretic mites. The minute before the treatment, the last mite jumped into a cell that was just capped. This mite will emerge in 14 days (if it jumped into drone comb). All mites in capped brood on day 0 survive the treatment.
Day 1: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 2: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 3: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 4: Treatment 2 kills all mites that emerged since day 0
Day 5: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 6: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 7: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 8: Treatment 3 kills all mites that emerged since day 4,
Day 9: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 10: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 11: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 12: Treatment 4 kills all mites that emerged since day 8
Day 13: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 14: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 15: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 16: Treatment 5 kills all mites that emerged since day 12, just before they jumped into brood cell again
If you cannot make a day, better go to a 3-day interval rather than a 5-day interval.
ROBBING: After the 5th treatment you have killed most of your mites.
OAV is not 100% effective so some may survive.
Mites might jump into cells earlier than day 5 (which is an average, and depends on the situation in the hive)
Most importantly: some treatments take place when the hive imports new mites. Especially the August treatment coincides with dying hives and while your treatment is killing most of YOUR mites, the bees are bringing in new mites from dying mite bombs. How do I know? I have mite bombs in my area, and I can tell you exactly when they die by monitoring my hives mite loads. Bees can bring in up to 1200 mites over a 3 day period.
If you find that mites on the bottom board don't drop to 5-20 after the 5th treatment
If you find that after the 5th treatment some hives (but not all, since not all hives find the same dying hive) your mite count is still between 300-1500 every 4 days, keep treating until the situation subsides.
Oxalic Acid Efficacy
Mites in capped brood survive OA treatment. Oxalic Acid kills ~99% of “phoretic” mites that are in the hive but not under capped brood.
Mite Biology
Mites spend about 5-11 days riding/feeding on bees in their “phoretic stage” after they emerge from capped brood and before they re-invade the next brood cell before it is capped. Therefore 4 day treatment cycles kill all mites that emerged since the last treatment
Bee Biology
Drones have the longest pupa stage (under capped brood); they emerge after 14 days. Therefore treatment cycles must last at least 14 days.
The recommendation “5 treatments, 4 days apart” is impractical for anyone other than small-scale, backyard beekeepers. Revisiting hives that many times is not practical for anyone with 100+ hives. Even with 30+ hives this approach is a challenge and impossible if the hives are not all in the same yard.
Large-scale beekeepers may use OAV to “knock back” the number of mites without hopes of ever eradicating most of them. Or they may use it as a one time treatment in December when there is no capped brood. But realistically, most large scale beekeepers use apivar strips (soaked with "Armitraz" miticide).
That is why Don Kuchenmeister (aka “Fat Bee Man” on youtube) recommends “three treatments 1 week apart as you get a new hive and then once a month, every month.” Basically he is perpetually knocking down the mites without ever hoping for large scale eradication and he does not have time to visit his hives more often. This may work; I have not tried it because it seemed too much of a "rule of thumb" based on nothing. Also, Don is now using apivar...
That is why Randy Oliver was so excited about his Oxalic Acid Extended release (OAE) “shop towel method” -- it requires only 1 trip to the hive (vs 5 for Oxalic Acid). But, three researchers have been working to obtain EPA approval for this method since 2017. Updates have been slow to come out and as of mid 2021, it has not been approved. Randy Oliver’s updates (update1 update2 ) inform us of many issues that are yet to be resolved:
Optimal concentration (OA/Glycerin)
Optimal delivery vehicle (cardboard/paper towel), more recently he is advocating Swedish dishtowels.
Best solvent (Propylene Glycol/Glycerin)
Effects of humidity/temperature on efficacy
Reasons for large variation in efficacy across hives
Talking to Krispin Given, who is in charge of the "ankle biter" bee breeding program at Purdue University, and who runs the Heartland Honey Bee Breeders Coop, their large-scale test of the shop towel did not prove to be effective. It also seems the Georgia study did not produce convincing results. It is unclear why but clearly there is more to learn before I tinker with it on my hives. I write more about this method and the original extended release application which seems to be more successful here.
My experiments show me that OAV is (for me) easier to apply and that OAE is not effective enough to rely on it alone.
The 4-day treatment interval is ambiguous. Randy Oliver recommends it since a recent article published jointly(!) in the American Bee Journal and in Bee Culture (Oct 2012) stated that the phoretic state lasts 5-11 days. These journals are not peer reviewed, however, so this is not a scientific statement; peer-reviewed journals suggest that 5-11 days is not a hard guideline:
The fraction of the phoretic mites that invade brood cells is influenced by the ratio of suitable-brood-cells to colony-size (Beetsma et al 1999). Since the number of suitable brood cells varies constantly, the duration-to-reinfestation varies, too.
Mites may have different origins, owing to transfer by drifting or by robbing. In recent years my own experiments have shown that mite imports can be a serious issue in the fall and some recommend treating until there are zero mites dropping the day after the treatment. I can attest that if a collapsing hive in your area is sending mites to your hive, you will need to treat longer than 5 times. I have seen mite imports of up to 500 over a 4 day period.
In my experience there seems to be ample evidence that 4 days is a rough guideline that works. It is sufficient for robust survival.
I have also observed that fall treatments can produce staggeringly high mite infestations within a single month(!). This can only be explained by transfer/robbing, not reproduction. Even in the summer I observed mite drops even after a full 16-day cycle. This implies new mite infestation through either a) < 100% OA efficacy, b) drifting/robbing, c) < 5 day brood re-invasion.
A picture speaks a 1000 words
treatment 1: right after honey harvest when mites explode and hive brood collapses
treatment 2: mid Sept robbing cleanup. Do 1 test treatment. If hives produce < 5 mites there is no need for additional treatments
treatment 2: Christmas when the hive is broodless. Wait for a sunny day to allow bees to move around in the hive and the vapor to penetrate the cluster. Do 1 test treatment. If hives produce < 5 mites there is no need for additional treatments
treatment 4: Optional mid April, just before the spring build up. I have skipped this in the past, it is optional. But the fewer mites you have to start the brood cycle from May-July, the smaller the exponential growth in mite numbers...
Oxalic Acid Vapor (OAV) Mite treatments must address two issues:
1) mite infestation (mites produced by your own hive)
2) mite importation (mites brought into the hive via robbing from dying mite bombs)
The Quick Answer:
Mites spend about 5 days in a “phoretic stage” riding/feeding on bees before jumping back into a brood cell to procreate. Oxalic Acid does not kill mites in capped brood. So, any mite that emerged after your last treatment from under capped brood can be killed if you treat every 4 days. A mite in a cell that was just capped on the day of your first treatment emerges 14 days later (it it jumped into a drone cell). So your treatments must cover at least 14 days or 5 treatments.
The 5x4 treatment plan:
1) Treatment Plan and Mite Stages
Day 0: Treatment 1 kills all phoretic mites. The minute before the treatment, the last mite jumped into a cell that was just capped. This mite will emerge in 14 days (if it jumped into drone comb). All mites in capped brood on day 0 survive the treatment.
Day 1: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 2: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 3: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 4: Treatment 2 kills all mites that emerged since day 0
Day 5: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 6: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 7: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 8: Treatment 3 kills all mites that emerged since day 4,
Day 9: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 10: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 11: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 12: Treatment 4 kills all mites that emerged since day 8
Day 13: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 14: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 15: Mites emerge from brood that was capped before day 0, they spend 5 days riding/feeding on the bees
Day 16: Treatment 5 kills all mites that emerged since day 12, just before they jumped into brood cell again
If you cannot make a day, better go to a 3-day interval rather than a 5-day interval.
ROBBING: After the 5th treatment you have killed most of your mites.
OAV is not 100% effective so some may survive.
Mites might jump into cells earlier than day 5 (which is an average, and depends on the situation in the hive)
Most importantly: some treatments take place when the hive imports new mites. Especially the August treatment coincides with dying hives and while your treatment is killing most of YOUR mites, the bees are bringing in new mites from dying mite bombs. How do I know? I have mite bombs in my area, and I can tell you exactly when they die by monitoring my hives mite loads. Bees can bring in up to 1200 mites over a 3 day period.
If you find that mites on the bottom board don't drop to 5-20 after the 5th treatment
If you find that after the 5th treatment some hives (but not all, since not all hives find the same dying hive) your mite count is still between 300-1500 every 4 days, keep treating until the situation subsides.
Oxalic Acid Efficacy
Mites in capped brood survive OA treatment. Oxalic Acid kills ~99% of “phoretic” mites that are in the hive but not under capped brood.
Mite Biology
Mites spend about 5-11 days riding/feeding on bees in their “phoretic stage” after they emerge from capped brood and before they re-invade the next brood cell before it is capped. Therefore 4 day treatment cycles kill all mites that emerged since the last treatment
Bee Biology
Drones have the longest pupa stage (under capped brood); they emerge after 14 days. Therefore treatment cycles must last at least 14 days.
The recommendation “5 treatments, 4 days apart” is impractical for anyone other than small-scale, backyard beekeepers. Revisiting hives that many times is not practical for anyone with 100+ hives. Even with 30+ hives this approach is a challenge and impossible if the hives are not all in the same yard.
Large-scale beekeepers may use OAV to “knock back” the number of mites without hopes of ever eradicating most of them. Or they may use it as a one time treatment in December when there is no capped brood. But realistically, most large scale beekeepers use apivar strips (soaked with "Armitraz" miticide).
That is why Don Kuchenmeister (aka “Fat Bee Man” on youtube) recommends “three treatments 1 week apart as you get a new hive and then once a month, every month.” Basically he is perpetually knocking down the mites without ever hoping for large scale eradication and he does not have time to visit his hives more often. This may work; I have not tried it because it seemed too much of a "rule of thumb" based on nothing. Also, Don is now using apivar...
That is why Randy Oliver was so excited about his Oxalic Acid Extended release (OAE) “shop towel method” -- it requires only 1 trip to the hive (vs 5 for Oxalic Acid). But, three researchers have been working to obtain EPA approval for this method since 2017. Updates have been slow to come out and as of mid 2021, it has not been approved. Randy Oliver’s updates (update1 update2 ) inform us of many issues that are yet to be resolved:
Optimal concentration (OA/Glycerin)
Optimal delivery vehicle (cardboard/paper towel), more recently he is advocating Swedish dishtowels.
Best solvent (Propylene Glycol/Glycerin)
Effects of humidity/temperature on efficacy
Reasons for large variation in efficacy across hives
Talking to Krispin Given, who is in charge of the "ankle biter" bee breeding program at Purdue University, and who runs the Heartland Honey Bee Breeders Coop, their large-scale test of the shop towel did not prove to be effective. It also seems the Georgia study did not produce convincing results. It is unclear why but clearly there is more to learn before I tinker with it on my hives. I write more about this method and the original extended release application which seems to be more successful here.
My experiments show me that OAV is (for me) easier to apply and that OAE is not effective enough to rely on it alone.
The 4-day treatment interval is ambiguous. Randy Oliver recommends it since a recent article published jointly(!) in the American Bee Journal and in Bee Culture (Oct 2012) stated that the phoretic state lasts 5-11 days. These journals are not peer reviewed, however, so this is not a scientific statement; peer-reviewed journals suggest that 5-11 days is not a hard guideline:
The fraction of the phoretic mites that invade brood cells is influenced by the ratio of suitable-brood-cells to colony-size (Beetsma et al 1999). Since the number of suitable brood cells varies constantly, the duration-to-reinfestation varies, too.
Mites may have different origins, owing to transfer by drifting or by robbing. In recent years my own experiments have shown that mite imports can be a serious issue in the fall and some recommend treating until there are zero mites dropping the day after the treatment. I can attest that if a collapsing hive in your area is sending mites to your hive, you will need to treat longer than 5 times. I have seen mite imports of up to 500 over a 4 day period.
In my experience there seems to be ample evidence that 4 days is a rough guideline that works. It is sufficient for robust survival.
I have also observed that fall treatments can produce staggeringly high mite infestations within a single month(!). This can only be explained by transfer/robbing, not reproduction. Even in the summer I observed mite drops even after a full 16-day cycle. This implies new mite infestation through either a) < 100% OA efficacy, b) drifting/robbing, c) < 5 day brood re-invasion.
A picture speaks a 1000 words
treatment 1: right after honey harvest when mites explode and hive brood collapses
treatment 2: mid Sept robbing cleanup. Do 1 test treatment. If hives produce < 5 mites there is no need for additional treatments
treatment 2: Christmas when the hive is broodless. Wait for a sunny day to allow bees to move around in the hive and the vapor to penetrate the cluster. Do 1 test treatment. If hives produce < 5 mites there is no need for additional treatments
treatment 4: Optional mid April, just before the spring build up. I have skipped this in the past, it is optional. But the fewer mites you have to start the brood cycle from May-July, the smaller the exponential growth in mite numbers...