Drones and Varroa: Half 2

Within the Could difficulty of this journal, Dr. Zac Lamas offered some findings of nice curiosity, concerning the distribution of varroa mites on drones as in comparison with that on employees. Aha, I assumed – this would possibly assist to clarify why mite wash counts after the honey movement typically improve extra strongly than anticipated. So I dove into some hives to find out to what extent the prevalence of drones within the hive could possibly be concerned.

In case you haven’t already watched it, take a look at Dr. Lamas’ video [[1]], during which he goes into a lot better depth than in his Could article. He explains that the drones perform as a “protecting cushion” for the colony, as a result of mites preferentially feeding upon them quite than the employees. Since drones usually are not concerned in transferring meals to different bees, nor in brood rearing, they’re extra expendable than the important nurse bees, and their presence could assist to cut back the impression of mites upon the nurse bees, in addition to cut back varroa-mediated virus transmission inside the hive, particularly early within the season, when the comparatively few mites current on the grownup bees in a colony could also be using (and feeding) predominately on drones.

Sensible query: The biotechnical methodology of utilizing drone brood to lure and take away varroa can cut back the variety of mites in a hive, however it will additionally take away the “protecting cushion” that these drones would have supplied had they been allowed to emerge. This tradeoff could be an attention-grabbing topic of analysis.

What particularly intrigued me about Dr. Lamas’ presentation have been two intriguing hypotheses:

That for the needs of varroa monitoring early within the season, sampling drones could higher replicate a colony’s total infestation charge than sampling bees shaken from the combs, and
That the post-flow disappearance of drones from the hive would trigger an considerable improve the varroa infestation charge of the employee inhabitants.

I discovered each of the above hypotheses to be believable and value testing.

Relating to the primary speculation, Dr. Lamas identified the issue with utilizing a sampling methodology based mostly on the idea of a random distribution of the parasite on the bees, when the parasite really happens in an aggregated distribution – suggesting that hand-plucking of drones could also be a greater methodology than a wash of a half cup of employees. Final month I confirmed my very own outcomes, evaluating the mite counts from employee samples to these of plucked samples of 25 drones from the identical combs.

This brings us to the second speculation, which to me was of far better curiosity, since it’d assist me to enhance my varroa mannequin [[2]]. Dr. Lamas’ proposed speculation was that when the drones “disappear” after the honey movement, the resultant shift of mites solely onto the employees would possibly assist to clarify why mite wash counts out of the blue improve, resulting in viruses overwhelming the colony.

I discovered the above speculation to be believable, and presumably explanatory for why my varroa mannequin typically underestimates the noticed fast improve in mite wash counts in employee samples taken in late summer season. So I made a decision that I’d higher examine.

Testing Speculation #2

First let me specify the query to reply:

Would the post-honey movement “disappearance” of drones from a colony lead to an considerable improve within the infestation charge of the grownup employees?

It occurred to me that this may be an easy arithmetical calculation. So for our calculation, let’s think about a hypothetical case during which all of the drones in a colony have been to out of the blue fly off, leaving a few of their mites behind.

To carry out the calculation, we have to know:

The entire variety of grownup bees within the hive previous to drone fly off.
The proportion of these bees that have been drones.
The mite infestation charge of the drones relative to that of the employees.
The variety of mites that the drones could be anticipated to hold out as they exited the hive.

We generally hear that colonies attain populations of as much as 60-80 thousand bees. However I used to be shocked by how tough it was to seek out arduous information supporting these numbers. So I made a decision that we must always roll up our sleeves and rely simply what number of employees and drones there have been in a few of my very own hives in late June and early July (on the finish of our honey movement).

Since I needed to get counts for each the employees and the drones, I couldn’t simply weigh the hive earlier than and after shaking out the bees – I wanted to first shake all the bees right into a cage and weigh them (this half was comparatively simple), then separate out the drones, and weigh them alone (that turned out to be a bit tougher than I hoped) (Figures 1 & 2).

Fig. 1 I used a really useful battery-powered gadget from China to shake the bees from every comb. Simply pull the set off, and in two seconds all of the bees are falling by means of the funnel (I used an ordinary bulk bee funnel). I constructed a particular hive physique “cage” to carry them for weighing.

By weighing the cage earlier than and after shaking the bees into it, I might decide the web weight of the bees. I additionally took a pattern (on ice) of no less than 100 employees for later weighing. After the primary hive, I first positioned and caged the queen previous to shaking.

Fig. 2 A view of the combs after shaking off the bees. The small quantity of bees you see have been returned foragers (which we then additionally shook into the cage).

It was comparatively simple to find out the burden of the grownup bee inhabitants. The difficult half was then to separate the drones from the employees. I had put in a queen excluder over the cage, in order that after weighing, I might enable the employees to exit (Determine 3).

Fig. 3 Younger employees keep away from mild; older employees fly in the direction of it. I discovered that what labored greatest was to first exchange the queen again into the empty hive (with its brood combs), then place the cage queen excluder facet of the cage down, and permit the youthful employees to climb by means of it onto the combs. Then I’d flip the cage over, and permit the older employees to exit up and out in the direction of the sunshine, leaving the drones nonetheless trapped inside.

Sadly, some employees stubbornly stay behind within the cage (there was a considerable hive to hive distinction), stopping me from merely weighing a cage filled with solely drones. I attempted transferring the remaining bees to a bucket to smoke the employees down by means of the excluder (Determine 4).

Fig. 4 Making an attempt to smoke the employees down. Didn’t work.

So how about knocking them out? (Determine 5).

Fig. 5 I attempted anesthetizing the drones and employees with CO₂, however they recovered too shortly to separate them by hand.

What I sadly wound up having to do was to drench the drones (and any remaining recalcitrant employees) with detergent resolution, and bag them for later drying, hand sorting, and weighing (Figures 6 & 7).

Fig. 6 We tediously hand sorted and weighed hundreds of drones and employees.

Fig. 7 By counting out 100 employees or drones and precisely weighing them, we might decide their common weights, after which calculate what number of of every have been within the hive.

We shook the bees from 5 comparatively robust double- and triple-deep hives. This was on the finish of our honey movement, and we solely shook out colonies during which I noticed numerous drones. I highlighted the outline “comparatively robust” because it was based mostly upon my evaluation of “cluster dimension” by trying down on the high bars – the colonies gave the impression to be “filled with bees.” What was eye-opening for me have been simply how few bees have been unfold out over the combs of the colonies that we shook (Desk 1).

Sensible word: A few years in the past, Dr. Eric Mussen had commented to me that our colonies in California by no means reached the power of these in Minnesota. So my outcomes could not replicate what you’d see elsewhere.

I put out a request for different beekeepers to shake a few of their hives. Invoice Elliot from Alabama did so from a 1½-story hive round 20 days after his honey movement ended, and I included his discovering. None of our shaken colonies have been wherever close to the generally acknowledged 50-60,000 bee vary. In the summertime warmth, the bees weren’t as packed on the combs as they’re when it’s cool.

My dangerous: In my varroa mannequin, I incorrectly assumed that there have been as many bees on a comb throughout summer season as there are when it’s cooler. That mistake results in beneath calculating the anticipated mite wash counts throughout summer season. I’ll deal with this in my subsequent article.

Anyway, we’ve now received a determine for the whole inhabitants of bees in post-flow hive. We now want a determine for the proportion of the inhabitants that have been drones. Currie and Jay [[3]] acknowledged that “Colonies with 24,000 – 27,000 employees include roughly 1800 drones,” which works out to them constituting a bit greater than 7% of the inhabitants. We didn’t discover wherever close to that top a proportion, with a few of the hives containing solely 2-3% drones. Anyway, for our calculation, let’s use the best drone proportion (5%) that I discovered in my hives.

The following determine that we’d like for the calculation could be the mite infestation charge of the drones relative to that of the employees – fortunately one thing that I already had from the drone sampling that I described final month (Desk 2).

I coloration coded the employee infestation charges in blue, and people of the drones in pink. In black boldface under I calculated the “multiplier” – what number of instances larger the infestation charge of the drones was, relative to that of the employees.

In all of the hives, the infestation charge of the drones was larger than that of the employees. For our calculation, let’s use the general common multiplier of 5.5% (which means that the common infestation charge of the drones was 5 and a half instances larger than that of the employees).

The final determine that we’d want for our calculation could be what number of mites the exiting drones would take with them. E.J. Steed collected flying (and thus presumably) older drones at drone congregation areas, and located that they have been infested by mites at about two-thirds the speed of employees sampled from brood combs in close by hives [[4]]. This means that drones that exit the hive take their mites with them. Dr. Lama’s information point out that drones sufficiently old to fly have been roughly as enticing to mites as have been employees of the identical age, so for my calculations I’ll assume that when a drone exits a hive, its infestation charge could be the identical as that of the employee common (versus employees sampled from the brood combs).

Let’s Do the Calcs!

OK, we’ve now received all the data that we have to calculate to what diploma a hypothetical fly-off of drones would improve the mite wash rely in a pattern of employees. So (as I’m susceptible to do) I took a while (really numerous time) to create a calculator [[5]] to see (Determine 8).

Fig. 8 Within the above calculation run, I arbitrarily assumed that previous to drone fly off, the employees had reached an infestation charge of 10 mites per half-cup pattern (a 3.2% infestation — a generally accepted motion threshold). The calculation signifies that even within the hypothetical case of the drones (infested at 5.5x that charge) out of the blue leaving the hive, their exit would solely lead to a minimal improve within the infestation charge of the employees. One other tantalizing speculation bites the mud.

Conclusions

Though the speculation that put up honey movement drone disappearance would lead to a critical leap within the mite infestation charge of the employees was compelling, my information and calculations don’t help it.

The reason for the fast improve within the infestation seems to be primarily because of a mixture of 4 components:

The exponential improve within the mite inhabitants, which doubles roughly every month [[6]].
The discount of the grownup employee inhabitants, which means extra mites per bee [[7]].
A lower within the quantity of sealed brood, which leads to a better proportion of mites on the grownup bees.
And doable immigration of mites because of employee drift or robbing.

Sensible utility: My measuring of the particular bee counts of my hives has opened my eyes to the truth that my varroa mannequin wants adjustment. I’ll go into better depth subsequent month.

Why Would Mites Desire Drones?

I want to thank Dr. Lamas for his spectacular physique of analysis. His findings on the choice by mites for drones (which my information affirm) are of nice curiosity, and I’m curious as to why, since their fats our bodies (varroa’s goal meals) usually are not as developed as these of non-foraging employees. Haydak [[8]] discovered that the fats our bodies in drones consisted of solely “just a few aggregations of cells, tough to seek out,” and that “no fat-body was present in drones 3 days outdated or extra.” Nonetheless, the hemolymph of freshly emerged drones accommodates comparatively extra glycogen (an power molecule) than in same-aged employees, and the protein and vitellogenin content material of drone hemolymph “will increase quickly inside the first days after emergence, reaching a peak on the third day and lowering after the primary week” [[9]]. So what’s it about drones that mites discover so enticing?

We clearly nonetheless have quite a bit to study varroa and their affinity for drones! I sit up for studying Dr. Lamas’ research once they turn out to be out there.

Acknowledgements

Thanks for the sector assist from Corrine Jones, Kamon Reynolds, Victoria Knight, and Rose Pasetes.

Citations and notes

[1] Hidden in plain sight: Varroa combination on grownup drones https://www.youtube.com/watch?v=mAsXFPakumU

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

[3] Currie, R & S Jay (1991) The affect of a colony’s queen state on the drifting of drone honey bees (Apis mellifera L.). Apidologie 22: 183–195.

[4] Steed, EJ (2023) Parasites and pathogens at honey bee mating websites, and the implications for monitoring colony well being. M.S. Thesis, The College of Waikato.

[5] I’d be pleased to share a duplicate for those who’re .

[6] See cell AG62 on the Present Model tab of my varroa mannequin.

[7] https://scientificbeekeeping.com/ipm-3-strategy-understanding-varroa-population-dynamics/

[8] Haydak, MH (1957) Adjustments with age within the look of some inside organs of the honeybee. Bee World 38: 197–207.

[9] Hrassnigg, N & Ok Crailsheim (2005) Variations in drone and employee physiology in honeybees (Apis mellifera). Apidologie 36(2): 255-277.

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