Last week, as we were getting ready to treat our colonies for varroa, Amanda discovered one that had Deformed Wing Virus. It is a particularly heartbreaking disease to find, since the predominant physical issue is that the bees have either shrivelled wings or no wings at all. Watching a wingless bee crawl around on the comb is sort of like watching a horse with no legs.
I asked Paul van Westendorp, B.C.’s provincial aplculturalist, if there is anything we can do to prevent this disease, which can be one of the expressions of a hive under stress with other dieases, such as varroa mites . I also asked him about optimal times for treating for mites with formic acid as I was concerned we were a little bit late this year. (As a side note, Amanda and I have adopted a general rule that we won’t use any synthetic chemicals in our hives and that the harshest treatments we will avail ourselves of are formic acid and oxalic acid, both natural compounds.)
For the record, here is Paul’s long reply, which I suspect will give beekeepers, particularly in British Columbia’s more temperate regions, some guideposts for when to treat and when to not. He also adds some sage advice about feeding, and about the need to retest your hives after treatment.
Addendum: After I posted this blog I received a note from Brenda Jager, the former bee inspector for Vancouver Island, who also added her thoughts. I have attached them at the bottom of Paul’s notes.
Am I correct to assume that your claim of DWV is based on your visual observation of adult bees displaying their wings, or did you have your bees analysed through PCR? In any event, I would not get overly concerned about it as DWV is virtually universally present in honey bees, including “apparently healthy bees”. This is not unique to bees in BC but it appears to be almost cosmopolitan.
As with any of the viruses associated with honey bees, their presence doesn’t necessarily lead to disaster. Their two-stage condition, latent and benign versus virulent is common to all and is generally triggered by other stress-related factors. These factors may not directly cause a virus to turn virulent but indirectly by causing the bee’s immune system to be compromised. Under those weakened conditions, the virus may realize its opportunity by becoming virulent.
It is widely accepted that the presence of Varroa has a huge influence on viral activity. By effectively controlling Varroa, less stress is being exerted on the bees allowing them to retain resilience and innate resistance. However, it doesn’t mean we should adopt the simplistic approach of “zero tolerance” to mites (i.e. when you see a mite, apply the chemicals). Instead, we should follow IPM principles where we accept some mites but only to a certain level. When the mite population passes that threshold level, only then does one apply treatment. The way to measure these levels is of course through regular monitoring.
With the weather we have been having, it is fine to treat with FA. It is good that you do a comparison of different treatments to determine efficacy. Because the nights are getting cooler, it is important that the time of initial application should be during the mid-day when the temperatures are sufficiently high. As the weather will inevitably turn cooler in the weeks to come, it is important to have FA treatment come to an end soon.
At the end of September, you should start doing your winter feeding. I generally recommend not to do winter feeding too early because if the weather is still good, there is no need to fill up the frames with stored syrup and allow the bees instead to nurture along late season brood. This brood is very valuable as these will be wintering bees that hopefully survive until spring.
The only other step you still need to do is at the end of October, by doing a mite test to determine mite levels. That date is important as it is the last window of opportunity to apply strips to control mites and have them removed by mid-December. If the levels are negligible on or about November 01, I would leave them alone until spring.
Paul van Westendorp
Note from Brenda Jager, former Vancouver Island bee inspector, added Friday, Sept. 12:
If you find DWV expressing at this time of year, the colony may be doomed. Usually high varroa or “was” high varroa, but what it means is the Queen is likely infected. I would replace the queen in the colonies showing DWV now. Do you want to carry a sick queen into winter? Do you want her to continue to lay infected eggs?
I start winter feeding any time after August 15th if the colonies are short of stores. Why? Use the old summer bees to put away the stores and the heat of the late summer early fall. Also, that feeding will stimulate more brood rearing. Wait until late September and the bees may not be able to put away adequate stores due to a drop in summer population and the colder weather – harder to evaporate. Also, I do not like to use my new winter bees (starting to hatch early to mid Sept) to do the work at this time. I get stores in early and then leave them alone once there is enough for winter. What about the brood? – there is plenty of room for stores and brood if the colony is not already plugged.
If the colony is heavy already why would you feed?