Drones and Varroa: Half 1

Within the Could concern of this journal, Dr. Zac Lamas requested “Why we aren’t we sampling drones” with a purpose to monitor the mite infestation stage of our colonies within the springtime? Since my sons and I carry out a large number of mite washes, I discovered his findings and proposed hypotheses to be of nice curiosity. So I pursued his suggestion that beekeepers examine the infestation charges of samples of hand-plucked drones to these of samples of bees shaken from the identical or adjoining combs.

As a queen breeder, I’ve after all paid consideration to the presence of drones (Determine 1).

Fig. 1 Drones are plentiful in our hives from the time we return from almond pollination till a minimum of early July, however I’d by no means thought of the potential of utilizing them for varroa monitoring.

So after all I used to be very interested by Dr. Lamas’ analysis, however his thesis is embargoed ‘til 2024. Luckily, he introduced a few of his very attention-grabbing findings on YouTube [[1]]. His information signifies that the infestation charge of grownup drones is far larger than that of similarly-aged grownup employees for the primary a number of days of their lives, after which the distinction seems to largely disappear.

The Proposed Hypotheses

Dr. Lamas proposed two intriguing believable hypotheses:

That for the needs of varroa monitoring early within the season, samples of drones might higher mirror a colony’s infestation charge than samples of (largely) employee bees shaken from the combs.
That {the summertime} shift of mites from grownup drones to grownup employees would appreciably improve the varroa infestation charge of the employee inhabitants.

Since I’ve spent quite a lot of time evaluating numerous strategies for monitoring varroa [[2]] and carry out 1000’s of mite washes every season, I discovered Dr. Lamas’ findings and proposed hypotheses to be of nice curiosity. So I adopted his suggestion for beekeepers to make use of his protocol to match the infestation charges of samples of hand-plucked drones to these of samples of employees shaken from the identical or adjoining combs. After that, I explored the speculation that the midsummer discount within the quantity of drones in a colony would lead to an considerable improve within the infestation charge of the grownup employees.

Monitoring of the Mite Infestation

In Built-in Pest Administration, one screens the infestation charge of the pest with a purpose to decide whether or not and when to take motion in opposition to the pest, weighing the injury brought on by the pest vs. the price of management. There’s a great dialogue on pest remedy thresholds at [[3]]. In brief, there are two generally confused phrases. Within the case of varroa administration:

The Financial Harm Degree: The infestation charge of mites that may trigger yield losses (in pollination worth or honey manufacturing) equal to the varroa administration prices (the extent at which it turns into value efficient to use remedy).

The Financial Threshold (remedy motion threshold): The varroa infestation charge (pest density) at which administration motion ought to be taken to proactively stop the growing mite inhabitants from reaching the financial damage stage.

The important thing idea is to be proactive, since we are able to predict the speed {that a} varroa infestation will improve in a non-resistant colony (Determine 2).

Fig. 2 The anticipated improve in a colony’s varroa inhabitants over time. I used the generally noticed intrinsic charge of inhabitants improve (r worth) of 0.021 [[4]]. The factor to remember is that with exponential improve, early intervention is important.

Sensible utility: Essentially the most economically-successful beekeepers that I do know try to take care of varroa ranges effectively beneath the financial damage stage always of the yr — they don’t wait till they see excessive mite counts!

How greatest to acquire a consultant and constant pattern?

The factor to remember is that there’s just one option to exactly decide the mite inhabitants in a hive — that’s to kill all of the bees and brood, after which rely each single mite (one thing that quite a few researchers spent tedious hours doing within the early years of varroa analysis [[5]]). However, for monitoring functions we try and take a consultant pattern of grownup bees or pupae, after which extrapolate the common infestation charge of the bees within the hive.

Of equal significance, samples have to be dependable and constant — two or extra samples taken from the identical hive ought to give you near the identical quantity.

As a result of inherent variation of the infestation charge from bee to bee, to extrapolate a colony’s common infestation charge from a pattern, the pattern should include sufficient bees to beat that variability, sometimes through the use of the Poisson distribution of possibilities to give you the minimal required pattern dimension [[6]]. For a mite wash, Dr. Katie Lee decided {that a} pattern of 300 bees was sufficient [[7]].

I’ve spent quite a lot of time evaluating numerous strategies for monitoring varroa and figuring out what can be one of the best consultant pattern [[8]], and have discovered that shaking bees from a body adjoining to brood and permitting the older bees to fly off, would offer a pattern consultant of the colony as an entire. However I collected that information late within the season when there have been few drones — I want to duplicate the examine within the springtime.

So despite the fact that a shook bee pattern is consultant of the mite infestation charge of the grownup bees within the colony, it have to be evaluated relative to the grownup bee-to-brood ratio on the time it was collected. Check out Determine 3.

Fig. 3 My varroa mannequin [[9]] calculates the estimated mite wash rely based mostly upon the inputted varroa inhabitants within the hive. And based mostly upon the inputted quantity of grownup bees and brood (the vertical ratio of sunshine orange to darkish orange), it estimates the proportion of mites which can be hidden within the brood (backside row), in addition to the anticipated mite wash rely (blue figures). Word that in swarming season (when there are almost as many pupae as there are grownup bees), 4 out of 5 mites will be within the brood — and thus not on the grownup bees (whether or not employees or drones). Which means one should interpret the mite wash rely appropriately.

The factor to remember is that any sampling of grownup bees early within the season will underestimate the infestation charge of the colony as an entire. Word within the determine above how the infestation charge of the grownup employees is low clear via the start of June (3 mites per half cup of bees), then seems to blow up by the top of August (growing over 9-fold to a rely of 28).

Sensible utility: As illustrated in Determine 3, a mite wash rely over 1 in April signifies that motion ought to be taken earlier than the honey stream, in any other case the colony’s infestation charge could have already allowed for DWV to go rampant by the point you pull your honey in mid-August.

Testing Speculation #1

Dr. Lamas questioned the efficacy of sampling employee bees to observe the varroa infestation stage of a colony early within the season. His proposed speculation is that taking a pattern of 40 drones from a brood body may present a extra consultant evaluation of the mite infestation charge of a colony as an entire than would utilizing the usual methodology of taking a half cup pattern of employees. So I roughly adopted Dr. Lamas’ advised protocol to match the infestation charges of samples of hand-plucked drones to paired samples of employees taken from the identical or adjoining combs. Helped by Jennifer Radke, Rose Pasetes, and Corrine Jones in late April and mid June, we dove into some high-mite colonies that I had moved dwelling for experimentation, and took matching samples of drones and employees to match their infestation charges (we used high-mite colonies in order that we’d get sufficient mites in every pattern to get good information to work with).

Discipline Observations

Most beekeepers discover that drones are extra prevalent in frames to the perimeters of the broodnest, however once I really began on the lookout for drones to pluck off, it shocked me to see simply how a lot they clumped collectively (Determine 4).

Fig. 4 A typical comb stuffed with drones exterior of the broodnest. It quickly turned obvious that it was typically tough to seek out the 40 drones on a brood body as advised by the protocol (since drones keep away from this space), and that any pattern of shook bees from an outer body may include a big share of drones.

I quickly observed that it was uncommon to discover a drone with out a minimum of yet one more drone close by, so if I plucked one, I’d transfer the forceps proper again to that space, and normally discover a minimum of a pair extra. I discovered many of the drones on a number of of the outer frames, generally solely on one aspect of the hive, in addition to on the underside board to the again of the hive (Determine 5).

Fig. 5 Throughout the scorching climate once we took the samples, drones have been typically clumped behind the underside board.

A query: After observing how drones are likely to clump collectively, it occurred to me that this gave the impression to be unbiased of temperature (I’m not discounting that they like cooler temperatures away from the brood nest). Since this clumping takes place in darkness, it’s affordable to imagine that drones are drawn to the odor of different drones. May this clarify the widespread statement that some colonies (particularly these and not using a laying queen) seem like magnets for drifting drones?

I additionally observed that there was typically a big distinction within the sizes of the drones in the identical hive. I typically discover this in colonies which have gone laying employee and produce stunted drones in prolonged employee cells, however this was in “regular” hives (Determine 6).

Fig. 6 Word the variations in sizes between the 4 drones on this comb. This quantity of variation was regular.

It instantly turned obvious to me that few beekeepers would have the persistence to pluck 40 drones from a brood body — firstly as a result of there are sometimes only a few drones on a brood body, and secondly as a result of I discovered that it could take an inordinate period of time to seek out, pluck, and efficiently place in alcohol 40 drones.

Sensible utility: I shortly dismissed the practicality of accumulating 40 drones for a pattern, so arbitrarily took samples of 25 (which most beekeepers would nonetheless possible discover to be too tedious). Even at a rely of solely 25, it was typically tough for me to gather various drone samples from the twenty frames in every of the seven double-deep colonies from which we collected the paired samples. And if a drone managed to fly off when dropped into the gathering cup, we generally needed to recount — which might have been an actual ache for a pattern of 40!

I took as many paired samples of drones (Determine 7) and shook bees from the identical or adjoining frames as we may spot drones on, taking the paired samples from combs all through the hive (drones first, then shaking or brushing bees into a bathtub). The shook bee samples typically contained just a few drones (which might be typical for the half-cup of shook bee methodology), however we didn’t take away them.

Fig. 7 I plucked the drones off the combs with insect forceps and threw them right into a Daybreak detergent answer for laundry (we double washed to verify full mite restoration). I then shook or brushed bees (predominantly employees) from the identical or dealing with comb into a bathtub, after which scooped up a stage half cup of bees (roughly 315 employees) for the matching paired pattern.

Since drones have been comparatively uncommon on brood combs, we checked all of the frames in every hive for the presence of drones, with a purpose to acquire as many paired samples from every hive as potential.

Outcomes

Let’s check out the outcomes of first hive from which we took paired samples (Determine 8):

Fig. 8 Outcomes from Hive A. All paired samples have been taken from the identical combs (or brushed from the interspace between adjoining combs). Every information level represents the infestation charges of two paired samples taken from a single colony, with the infestation charge of the shook bees on the blue x-axis, and that of the drones on the pink y-axis. The typical values for the 2 varieties of samples are indicated, and on this chart I’ve additionally indicated the variance for every sort.

Interpretation: On this colony there was certainly a correlation between the infestation charges of the 2 varieties of samples (that of the drones being over 6x increased), however with a really low correlation coefficient (not proven) as a result of far larger deviations from the typical of the drone samples relative to these of the employee samples (examine the pink variance arrow for the drone samples to the blue arrow for the shook bees).

We might anticipate variation within the employee infestation charges, since they’re sometimes increased in samples taken from combs containing brood, however we’ll want to attend till Dr. Lamas publishes his outcomes to see whether or not the identical holds true for drones. The bigger diploma of variation within the drone samples is probably going partially as a result of smaller variety of bees concerned, however it’s unrealistic to suppose that any beekeeper would hand pluck 315 drones for mite monitoring.

We continued sampling six extra hives, some loaded with drones, some containing just a few (the variations within the quantities of drones in comparable colonies sitting aspect by aspect shocked us). I collected as many paired samples as potential from every hive, generally with all of our eyes looking for sufficient drones to make up a pattern of 25 (Figures 9-14).

Fig. 9 Outcomes from Hive B. Though we may solely spot sufficient drones for 4 samples, much like Hive A there was far larger variation within the drone samples than for the shook bee samples. Any one of many shook bee samples would have been consultant of the whole-hive varroa infestation charge — one thing that would not be stated for the drone samples.

Fig. 10 Outcomes from Hive C. This poor colony had an especially excessive mite infestation charge, and a larger diploma of variation within the shook bee samples than in different hives. Nonetheless, the usual deviation for the drone samples was over twice that of the shook bee samples. For these paying consideration, the infestation charges of the drones that exceeded 100% imply that there have been extra mites than drones.

Fig. 11 Outcomes from Hive D. Just like the opposite hives, a single pattern of 25 drones wouldn’t have been a dependable indicator of the colony’s general infestation charge. However, the shook bee samples have been remarkably constant.

Fig. 12 Outcomes from Hive E. Once more, the shook bee samples all fell in the identical vary, in comparison with the drone samples, which diverse extensively.

Fig. 13 Outcomes from Hive F. We may solely discover sufficient drones for 2 paired samples. The infestation charges of the shook bee samples have been almost similar, in comparison with drone samples that differed by 20% to both aspect of the typical.

Fig. 14 Outcomes from Hive G, from which we have been in a position to take 10 paired samples (two precisely overlapped). Once more, the shook bee samples diverse solely barely, whereas the drone samples have been all over.

The Take House

Dr. Lamas’ findings concerning the distribution of mites on drones of various ages are of nice curiosity, and should assist us to raised perceive varroa and virus dynamics within the hive. However so far as utilizing samples of drones that aren’t age marked with a purpose to monitor a colony’s varroa infestation charge, we e discovered that taking a pattern of even 25 drones was far tougher and time-consuming than shaking a pattern of a half cup of bees. Our findings from the seven hives from which we took paired samples in late April via mid-June indicated {that a} pattern of 25 drones wouldn’t be a dependable indicator of the general infestation charge of the grownup bees within the hive, whereas a shook or brushed pattern of a half cup of largely employee bees typically would. In reality, inadvertently together with just a few younger drones in such a pattern may skew the mite rely appreciably upward.

Sensible utility: For varroa monitoring functions, we’re sticking with mite washes of a half cup of bees shaken from a comb adjoining to the broodnest.

The principle factor to remember is that early within the season many of the mites are within the brood, so it’s no shock that the infestation charge of the employees will appreciably improve later within the season. So a mite wash of shook grownup bees have to be interpreted in that gentle — in our operation, we’d proactively deal with if our colonies exhibited infestation charges of greater than a single mite in a half cup of bees in April or Could.

Subsequent month I’ll element how I examined Dr. Lamas’ second speculation, since it’d assist to clarify the surprisingly sudden improve in infestation charges in August and September.

Citations and Notes

[1] SBGMI Presents: “Why don’t we pattern drones?” https://www.youtube.com/watch?v=mAsXFPakumU

[2] Reconnaissance Mite Sampling Strategies and Thresholds https://scientificbeekeeping.com/fighting-varroa-reconnaissance-mite-sampling/ (first printed in March 2007 ABJ)

Re-Evaluating Varroa Monitoring:

Half 1- Strategies https://scientificbeekeeping.com/re-evaluating-varroa-monitoring-part-1/ (first printed in March 2020 ABJ)

Half 2- Questions on Sampling Hives for Varroa https://scientificbeekeeping.com/re-evaluating-varroa-monitoring-part-2/ (first printed in April 2020 ABJ)

Half 4- What About Letting the Shook Bees Fly Off? https://scientificbeekeeping.com/re-evaluating-varroa-monitoring-part-4/ (first printed in June 2020 ABJ)

[3] https://cropwatch.unl.edu/economic-injury-level-and-economic-threshold-ipm

[4] The r worth is barely increased within the spring, and decrease later within the season. See column AZ65 on the Present Model tab at https://scientificbeekeeping.com/randys-varroa-model/

[5] My hat is off to John Harbo, Jeff Harris, Lilia De Guzman, José Villa, and Bob Danka for his or her work!

[6] https://scientificbeekeeping.com/re-evaluating-varroa-monitoring-part-2/ (first printed in April 2020 ABJ)

[7] Parasite Monitoring https://scientificbeekeeping.com/sick-bees-part-11-mite-monitoring-methods/ (first printed in August 2011 ABJ)

[8] Re-Evaluating Varroa Monitoring:

Half 1- Strategies https://scientificbeekeeping.com/re-evaluating-varroa-monitoring-part-1/ (first printed in March 2020 ABJ)

Half 2- Questions on Sampling Hives for Varroa https://scientificbeekeeping.com/re-evaluating-varroa-monitoring-part-2/ (first printed in April 2020 ABJ)

Half 3- How Does Mite Distribution Range Body-to-Body in a Hive? https://scientificbeekeeping.com/re-evaluating-varroa-monitoring-part-3/ (first printed in Could 2020 ABJ)

Half 4- What About Letting the Shook Bees Fly Off? https://scientificbeekeeping.com/re-evaluating-varroa-monitoring-part-4/ (first printed in June 2020 ABJ)

[9] https://scientificbeekeeping.com/randys-varroa-model/

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