Varroa Control- from synthetic chemicals to IPM and organic compounds
Varroa Destructor is parasitic mite that infests honeybee colonies. The mite is destructive to colonies through vectoring baterium and viruses whilst feeding. During its breeding cycle spent in the brood cell, it feeds by puncturing a hole in the larvae creating an open wound through which it sucks out the developing fat-body (equivalent to a liver) of the larvae. Multiple mites will make multiple wounds. Varroa mites have been proven to be vectors for a number of bacterial infections and viruses transmitted directly whilst feeding and expanding around the feeding hole wound site. Common bacterial infections such as the highly contagious foulbroods are caused by bacteria. Research has shown that causative bacterium have been found living and growing around the wound site. As well as being a vector for bacterial infection, mites also vector viruses. Commonly and easily identified symptoms of viral infection are from Deformed Wing Virus (DWV) and Kashmir Bee Virus (KBV), both crippling and deleterious to the colony. KBV along with other Chronic Paralysis Virus' (CPV) infections are becoming increasingly prevalent. We have experienced CPV (identified by staged symptoms) in our apiaries and it is heartbreaking to see. All CPV infections are highly contagious and easily spread throughout the colony simply by the action of the bees trying to rid the colony of infected bees and by the action of the guard bees trying to prevent entry to infected bees. There is no medical relief available. Although a colony can overcome the infection given time, the extreme contagiousness means it easily spreads from an infected colony to its neighbours. An unfortunate side-effect of us trying to save an infected colony resulted in the loss of the infected colony, it's adjacent neighbour, and an expanding recently re-queened nuc'. Fortunately, noticeable infection in two other colonies cleared up, but they were much smaller units and less active. It always seems to be the biggest and most prolific colonies that suffer the most.
Bacterial and viral transmission isn't limited to the developing larvae. Part of the mite's lifecycle is spent mobile attached to and feeding from parasitised bees. They tuck themselves right in under the bees' protective plate and there, as with the larvae, pierce a feeding hole and suck out the bees' fat-body. Attendant with this feeding is of course vectoring of the same bacterium and viruses. Transmission of adult bee viruses can be particularly virulent. Infected larvae tend to be removed either before they emerge naturally, or soon after emerging as baby bees. When adult bees are infected, transmission can occur during communication from food exchange (trophallaxis), antenna touching, and generally moving around a crowded living compartment. Infection spread within a seriously infested colony can be swift and devastating.
There is next to no medical assistance when it comes to relieving bee pathogens. In "the good ole days" there were antibiotic remedies for foulbrood and pyrethroid treatments against Varroa mites. Misuse by beekeepers who thought better than to follow the manufacturers' direction soon created a scenario of antibiotic and pyrethroid resistance making them ineffective. The widespread prophylactic us of antibiotics within the intensive meat producing industries has further exacerbated antibiotic resistance, especially for the most common ailments. Other bacterial remedies were also available but have gone out of favour due to being found to be carcinogenic. There has never been anti-viral remedies for bee diseases. Bee farmers globally hold out hope for further development in combating bee viruses developed from RNA techniques. In the meantime, focus is very much on maintaining good levels of nutrition and upholding good standards of husbandry on one hand, whilst combating the vectors for disease spread on the other. Systematic and concerted efforts to control the varroa mite is pivotal in this battle.
For an ever expanding cohort of hobby beekeepers who choose to adopt a hands-off, or natural (sic), method of keeping bees. It is perfectly acceptable to do nothing to control Varroa, the main vector of infections in bees, and simply accept that what should be a perfectly healthy, long lived, and productive colony, will die-out as a result of infestation and infection. The associated impact upon the wider environment and local bee colonies is unimportant to them. For us at De-Bees that scenario is unacceptable and to this end we endeavour to use whatever tools are available to us to mitigate the risk posed by the Varroa mite.
For an ever expanding cohort of hobby beekeepers who choose to adopt a hands-off, or natural (sic), method of keeping bees. It is perfectly acceptable to do nothing to control Varroa, the main vector of infections in bees, and simply accept that what should be a perfectly healthy, long lived, and productive colony, will die-out as a result of infestation and infection. The associated impact upon the wider environment and local bee colonies is unimportant to them. For us at De-Bees that scenario is unacceptable and to this end we endeavour to use whatever tools are available to us to mitigate the risk posed by the Varroa mite.
In earlier years we relied heavily upon synthetic chemicals to kill the mites, more often than not on bi-annual basis. Gradually, following much experimentation including using predatory mites, and developing a greater understanding of bee husbandry, we are far less reliant upon synthetic chemicals. For several years now we have used Oxalic Acid Dihydrate (OA) variously applied directly as a liquid, vapourised using a Varamous device, and more recently introduced by sublimation using an InstantVap device. Other available devices for sublimation were too expensive and cumbersome for our small enterprise. The InstantVap device has given an order of magnitude change for the better in using OA.
As with all products there is a recommendation for use, and as with all OA remedies the recommendation is to use it during a broodless period. To be optimally effective, using OA for Varroa control takes advantage of the mite spending a period of time outside the brood cell attached and feeding from a parasitised bee. The OA gas molecule is too large to penetrate wax cappings and is short lived so has no effect on the mite breeding cycle. Recommending use during a natural broodless period presents a problem in temperate climates due to the short or non-existent broodless period. Certainly where we are in the Southwest (UK) there might be a very short broodless period but this would be during the coldest weeks when the bees are tightly clustered. Application of a contact control method onto a cluster is pointless as it will only make contact with the outer bees. It is known that liquified OA has a detrimental affect upon bees and brood, perhaps because they eat the sugar based carrier solution and condense. Sublimation is an altogether different concept so the question was, does this method have a equally detrimental effect on bees and brood. Time for more experimenting. First some research and understanding.
As with all products there is a recommendation for use, and as with all OA remedies the recommendation is to use it during a broodless period. To be optimally effective, using OA for Varroa control takes advantage of the mite spending a period of time outside the brood cell attached and feeding from a parasitised bee. The OA gas molecule is too large to penetrate wax cappings and is short lived so has no effect on the mite breeding cycle. Recommending use during a natural broodless period presents a problem in temperate climates due to the short or non-existent broodless period. Certainly where we are in the Southwest (UK) there might be a very short broodless period but this would be during the coldest weeks when the bees are tightly clustered. Application of a contact control method onto a cluster is pointless as it will only make contact with the outer bees. It is known that liquified OA has a detrimental affect upon bees and brood, perhaps because they eat the sugar based carrier solution and condense. Sublimation is an altogether different concept so the question was, does this method have a equally detrimental effect on bees and brood. Time for more experimenting. First some research and understanding.
Correlating the bee brood-cycle with the Varroa mite brood-cycle.
The starting point was to understand the brood cycle for the bees and the mites. The bee brood-cycle is fixed within a day or so. Similarly the mite brood-cycle is fixed, again within a day or so and dependent upon the bee brood. Critical to this understanding was the periods when the mite was outside the brood cell, for this is when the OA is effective. We chose a strong and expanding nuc' to experiment with. The objective was to ascertain whether multiple OA sublimations has a detrimental effect on the colony as a whole but in particular the brood at all stages. The outcome was there were no identifiable deleterious affects on brood, bees, or development of the colony as a whole, following multiple dosing with OA sublimation at regular intervals over the defined brood-cycle period of time.
We have been using the 5-cycle method throughout the season for a couple of years and have found it particularly effective in controlling the mite loading at the beginning of Spring colony expansion. Bee brood-cycle period is 21-days give or take a day and a couple of days longer for drone brood. The female Varroa mite enters the cell after the egg becomes a larvae and before it is capped for the larvae to begin the metamorphosis process. The objective is to kill the mobile mites before they enter the cell taking into consideration there will be bees and mites inside brood-cells occupied before the control method begins. A 4-day cycle across the 21-day brood period is chosen to allow for multiple applications and the likelihood of rain stopping play. We monitor and record Varroa loading by counting the natural mite drop on a monthly basis as part of our IPM strategy. Counting natural mite drop has shown itself to be inaccurate but indicative all the same. Anything invasive such as a mite wash is impractical and in itself detrimental to the colony during the cold season and for repeated use. So counting dead mites on the board is the best option. It gives good indication of the effectiveness of the control method and that's the important factor. Accuracy is not altogether relevant.
We have been using the 5-cycle method throughout the season for a couple of years and have found it particularly effective in controlling the mite loading at the beginning of Spring colony expansion. Bee brood-cycle period is 21-days give or take a day and a couple of days longer for drone brood. The female Varroa mite enters the cell after the egg becomes a larvae and before it is capped for the larvae to begin the metamorphosis process. The objective is to kill the mobile mites before they enter the cell taking into consideration there will be bees and mites inside brood-cells occupied before the control method begins. A 4-day cycle across the 21-day brood period is chosen to allow for multiple applications and the likelihood of rain stopping play. We monitor and record Varroa loading by counting the natural mite drop on a monthly basis as part of our IPM strategy. Counting natural mite drop has shown itself to be inaccurate but indicative all the same. Anything invasive such as a mite wash is impractical and in itself detrimental to the colony during the cold season and for repeated use. So counting dead mites on the board is the best option. It gives good indication of the effectiveness of the control method and that's the important factor. Accuracy is not altogether relevant.
Before OA sublimation at each cycle, mites are counted and boards are cleaned. In mid-February the pre-cycle count indicated lower mite level than January's end of month count. This was a likely indicator of a broodnest and start of mite breeding cycle. It only takes a few mites to multiply to infestation proportions as colony Spring expansion develops. Counting the mite drop on the boards is straight forward and easy to do. It doesn't need to be accurate down to the nearest mite and we round up to the next 5-count, even from a count of 1. The total mite drop count is entered into a table which I developed to calculate the daily drop and then indicates whether this is high or low based upon NBU recommendation, very much a rule of thumb type calculation used as an indicator not an exact calculation. Expectation when the 5-cycle period is used after a broodless period is that the first mite count would be extremely high, remain relatively high for the second, then drop off dramatically for the next cycles tending toward zero after the final cycle. Similar was expected knowing there was a broodnest, but given presence of brood prior to sublimation brood, the drop in mite count wasn't expected to be so dramatic.
Table shows the mite count at each cycle of a 5-cycle sublimation with and without significant amount of brood being present.
The table above was created to give a pictorial representation of the brood cycle within the hive. The recommendation is for OA to be applied during a broodless period in order to maximise mite kill. But what happens when there is a broodnest? Many colonies were suspected of maintaining a broodnest throughout Winter, so what would be the predicted outcome of applying OA control measure on an established broodnest? Expectation was that the mite drop would be significant but not dimish to zero/day after the 5-cycle control. The table shows the mite count after each cycle of the 5-cycle period at one of our apiaries. By way of explanation; the numbers under the table in yellow are the mite drop on day 4 after the sub~. In red the mites killed cumulatively. Moving up the table the green numbers represent the brood cycle. The sub~ day is coloured black. Following the purple outline, everything to the left represents existing brood, to the right future brood. Above the horizontal purple box is future brood. Everything to the right in line and below the horizontal box is continuing brood cycle. EG=egg, OB=open brood, SB=sealed brood. The table indicates pictorially the previous, existing, and ongoing brood cycle of the broodnest. It can be seen that although a particular sub~ cycle may kill all the mobile mites, there are others waiting to emerge in the capped (SB) cells. Female mites (the males die in the cell) emerge with the baby bees after 21-days. Mature female mites enter cells on day 7, just before it is capped on day 9. I have a suspicion that mature mites do not spend very long outside the cell and may enter as soon as they come across a ready cell.
The end of January monthly count indicates a significant infestation of mites in the majority of colonies. We knew from examining the boards that they all maintained a broodnest throughout winter and that most began Spring expansion in early February. Anybody with a count exceeding 400 was destined to suffer detrimental effects before the end of Spring, probably collapse altogether. High infestation also poses a risk to colonies within the same apiary and to the wider environment. The table shows the expected massive mite kill after sub~2, dropping off but remaining relatively high for the next cycles, finally dropping off after sub~5. The end of March count indicates a low natural drop, but understanding of the colony's condition is essential when interpreting this count. Overall it is known to be false. For example Kers.10 count indicates a satisfactory low level mite drop. But when interpreted in context of knowing the colony's broodnest status it is certainly false. Kers.10 is (confirmed 2nd April) sat on a broodnest consisting of 4-frames, 3 of which are almost entirely SB, so roughly 21000 sealed cells and 7000 soon to be mite ready cells. The fat end of 30000 cells potentially harbouring mites.
In summary, there is a reduction in the potential mite kill after sub~2 with the potential kill rate significantly reducing after sub~3. If the broodnest is established at a good size (say more than a single frame) prior to the start of the control, there is likely to be a high number of mites remaining at the end of the 5-cycle period. The likelihood of this being the case is indicated by Kers.10 final count. The mite count does not tend to zero/day. It is also indicated in Kers.9 which (confirmed 2nd April) has maintained a sizeable broodnest all Winter, including drone brood. Kers.9 expanded to a point where they condidered themselves suitable for a new queen and superceded. Of course, without mature drones it was pointless and they became queenless. The upward trend in mite kill indicates a lack of new cells for the mites to infest, and instead succumbed to the OA sublimation control method.
Satisfaction with this method already runs very high. Seeing a wide spread of mites across the board indicates that not only are they dropping at the area of the broodnest, but also being groomed off away from the nest. The cumulative mite count indicates a significant number of mites that will not infest the colonies during the rapid Spring expansion. Although the daily mite count is higher than we'd like see tending toward zero/day,, it is below the maximum recommended level given in the guidance we use. We are confident that now the mite loading is reduced, the colonies will be able to deal with the remaining mites themselves. Any colonies that appear to be struggling to control their mite loading will be given further assistance with an extended time release mitacide. Application of a mitacide will of course remove them from Spring honey production, they can build comb instead and be at peak performance for Summer honey production.
So wadda we reckon? The InstantVap is a bloody marvelous device and OA is a bloody marvelous compound. So in a word, bloody marvelous! Most reports on its use will tell you how fast the application is, and the application itself is indeed fast. Roughly 20-sec per colony. But there's no point in using a control method without monitoring its effectiveness. So add on the mite count time, the board clean time, the note taking time, the data transfer and analysis afterwards time, it takes ages. But at the end of the day we're not blindly doing something which may or may not be effective in achieving the desired outcome of a low Varroa mite loading at colony level.
The end of January monthly count indicates a significant infestation of mites in the majority of colonies. We knew from examining the boards that they all maintained a broodnest throughout winter and that most began Spring expansion in early February. Anybody with a count exceeding 400 was destined to suffer detrimental effects before the end of Spring, probably collapse altogether. High infestation also poses a risk to colonies within the same apiary and to the wider environment. The table shows the expected massive mite kill after sub~2, dropping off but remaining relatively high for the next cycles, finally dropping off after sub~5. The end of March count indicates a low natural drop, but understanding of the colony's condition is essential when interpreting this count. Overall it is known to be false. For example Kers.10 count indicates a satisfactory low level mite drop. But when interpreted in context of knowing the colony's broodnest status it is certainly false. Kers.10 is (confirmed 2nd April) sat on a broodnest consisting of 4-frames, 3 of which are almost entirely SB, so roughly 21000 sealed cells and 7000 soon to be mite ready cells. The fat end of 30000 cells potentially harbouring mites.
In summary, there is a reduction in the potential mite kill after sub~2 with the potential kill rate significantly reducing after sub~3. If the broodnest is established at a good size (say more than a single frame) prior to the start of the control, there is likely to be a high number of mites remaining at the end of the 5-cycle period. The likelihood of this being the case is indicated by Kers.10 final count. The mite count does not tend to zero/day. It is also indicated in Kers.9 which (confirmed 2nd April) has maintained a sizeable broodnest all Winter, including drone brood. Kers.9 expanded to a point where they condidered themselves suitable for a new queen and superceded. Of course, without mature drones it was pointless and they became queenless. The upward trend in mite kill indicates a lack of new cells for the mites to infest, and instead succumbed to the OA sublimation control method.
Satisfaction with this method already runs very high. Seeing a wide spread of mites across the board indicates that not only are they dropping at the area of the broodnest, but also being groomed off away from the nest. The cumulative mite count indicates a significant number of mites that will not infest the colonies during the rapid Spring expansion. Although the daily mite count is higher than we'd like see tending toward zero/day,, it is below the maximum recommended level given in the guidance we use. We are confident that now the mite loading is reduced, the colonies will be able to deal with the remaining mites themselves. Any colonies that appear to be struggling to control their mite loading will be given further assistance with an extended time release mitacide. Application of a mitacide will of course remove them from Spring honey production, they can build comb instead and be at peak performance for Summer honey production.
So wadda we reckon? The InstantVap is a bloody marvelous device and OA is a bloody marvelous compound. So in a word, bloody marvelous! Most reports on its use will tell you how fast the application is, and the application itself is indeed fast. Roughly 20-sec per colony. But there's no point in using a control method without monitoring its effectiveness. So add on the mite count time, the board clean time, the note taking time, the data transfer and analysis afterwards time, it takes ages. But at the end of the day we're not blindly doing something which may or may not be effective in achieving the desired outcome of a low Varroa mite loading at colony level.
Side note: this is a new page and may contain gibberish which will get edited out eventually. All of the content is my own observations and experimentation. The tables and derivations are my own design and making. Cited NBU advice is from a graph published years ago and is probably not up to date. The intended outcome for the control methods we use is to maintain the mite loading at a low level, ideally tending towards zero, on a daily mite drop basis. We endeavour to help our bees help themselves by preventing Varroa mite infestation overwhelming the colony as a whole.