A Research on Bee Drift and Mite Immigration: Half 5


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A Deeper Look into our Knowledge. 1

Was Robbing Concerned with Mite Immigration?. 6

Dialogue on Robbing. 8

Research Wrap Up. 9

Assessment.. 10

Subsequent Month. 10

Acknowledgements. 11

Citations and Notes 11



Half 5

Randy Oliver


First printed in ABJ June 2023



There was clearly drifting of bees from the collapsing colonies, with them presumably carrying hitchhiking mites.  However averages and statistics are usually not practically as informative as wanting on the information from every particular person hive.


A Deeper Look into Our Knowledge

Query:  Is mite immigration regular or episodic?

Let’s take a look at the semi-weekly mite drop counts over time for the Receiver hives, once more damaged down by distance from the Donors (Determine 1).

Fig. 1.  Mite immigration adopted a remarkably clean and constant curve, peaking in October (coinciding not solely with Donors collapsing, but in addition when their mite ranges peaked).  The coloured columns point out the common semi-weekly per-hive mite drop for every distance group of Receiver hives; the black columns are the complete variety of drifted bee tags recovered on every date. The low preliminary price of tag restoration is probably going an artifact of us not starting our tagging of younger bees till 17 September, from which we wouldn’t count on any flight or drift till a minimum of a number of days later.

The tall purple columns point out greater mite drops within the single Receiver at 15 ft, however surprisingly, there wasn’t a lot distinction in common mite drops between the 60- and 500-foot teams of Receivers.

Additionally word the substantial lower in mite immigration starting on 25 October.  It didn’t look like any change within the climate (Determine 2).

Fig. 2.  Days had been heat and sunny all through the length of this examine.

One factor that had modified was that the high-mite Donors had largely collapsed by that point, so the quantity of obvious mite immigration did seem to coincide with the 2 episodes of Donor colonies collapsing.

Query:  How intently did mite immigration correlate with the drifting of tagged bees?

The black columns in Determine 1 point out that there was typically a correlation between the drifting of tagged bees and mite immigration.  However since we had been deliberately tagging bees through the course of of every Donor colony collapsing, it’s not stunning that there can be a correlation.  So let’s break the info down by hive (Determine 3).  (Reminder on hive numbering:  D1 means Donor #1; R1 means Receiver #1).

Fig. 3.  For some Receivers, the correlation between mite drop and incoming drifted tagged bees was sturdy; for others it was weak.  So it’s tough to attract conclusions (particularly because the probability of a drifted bee carrying a number of mites is probably going random).  Once more, since we tagged such a low proportion of bees per Donor, it’s not clear whether or not the immigrated mites got here primarily from the Donors, or from unknown colonies (managed or feral) within the neighborhood.

An vital qualifier so far as contemplating this as a longitudinal examine:  This examine was set as much as decide whether or not the relatively-sudden will increase in mite infestation charges in our colonies was because of mite immigration, and from colonies at what distance.  For that cause, we deliberately tagged bees within the Donor hives after we noticed that their mite ranges had been peaking and so they had been present process the method of collapse.  Thus the general correlation between tagged bee restoration and mite immigration is probably going a minimum of partially an artifact of the timing of after we tagged bees.  So though the mite drop counts qualify as a longitudinal examine, our tag restoration information are skewed by our uneven tagging of bees week by week.  Thus the emigration of our tagged bees could not mirror the precise timing and charges of emigration of the variety of untagged mite-carrying bees that drifted to the Receivers (and their related switch of mites).

Interpretation:  It’s not clear whether or not the drifting of tagged bees (and mites) was the results of easy diffusion of bees drifting in each instructions (Donor-to-Receiver and Receiver-to-Donor), or fairly because of there being an elevated exodus of bees from colonies as they collapsed.  Nonetheless, regardless of the vast hive-to-hive variations within the complete drifted tag recoveries and complete obvious mite immigration over the course of the whole examine, it might assist to interrupt that information down additional.

One other approach of our information is to make use of a scattergram (beginning on 1 October after we began to get well tags).  This enables us to find out, for every hive test, the diploma of correlation between the variety of drifted tags, relative to the corresponding mite drop depend for that particular time interval, unbiased of calendar date (Determine 4).

Fig. 4.  Considered this manner, there was a remarkably sturdy correlation between the variety of drifted tags from the Donor hives, relative to the variety of apparently immigrated mites on the stickyboards (the counts are usually not ordered by date).

Since we don’t know for positive the supply colonies for all of the immigrated mites (and because the tagged bees represented such a small proportion of the Donor hive employees), it’s not possible to attract agency conclusions from this chart ― the correlation could nicely have been even greater if there had been no different colonies inside flight vary, or if we had tagged a bigger proportion of the employees within the Donor hives.

Interpretation:  Though tagged bee drift and mite immigration each coincided with the collapses of the Donor colonies, we didn’t start tagging bees early sufficient, or persistently sufficient, to inform whether or not the method of collapse prompted an exodus of drifting mite-ridden bees (Mite Bombs), or whether or not it was merely because of regular drifting.  One would want to repeat the examine ― tagging the identical variety of bees every week — to seek out out.  In any case, it actually seems that there was a robust correlation between the drifting of tagged bees and mite immigration.  That reality means that the immigrated mites did a minimum of largely come from the Donors, fairly than from unknown hives, since these unknown colonies would have wanted to have been shedding mites on the identical days that our Donor hives had been dispersing drifting tagged bees.

We are able to take even a more in-depth take a look at our information, which I’ve damaged it down in two charts — one for the shut Receivers, the opposite for these within the 500-foot group (Figures 5 & 6).  Do not forget that some Donors collapsed in mid-to-late September, the remainder in mid-to-late October, which is mirrored within the stickyboard counts (on this case ordered by date).

Fig. 5.  For the Receivers positioned close to the Donors, it seems that some had been “mite magnets” (purple and purple), whereas others suffered from little mite immigration.

Fig. 6.  Much like the shut Receivers, a few of these more-distant Receivers persistently dropped extra mites than others, unbiased of their distance from the Donors.

Interpretation:  What surprises me is the consistency of the obvious mite immigration into among the hives, whereas in others it will go up and down (as I’d count on from random drift).  And so far as my nagging query about whether or not the high-count receivers had been producing their very own mites, check out the sky-high stickyboard counts of R5 and R7 (purple columns), which I inspected on 17 October, and confirmed that they had been primarily mite free.

Be aware that by early November, the stickyboard counts dropped to very low numbers, regardless of there nonetheless being loads of bee flight because of the climate remaining heat.

We’ve got just one final query to go:

Was Robbing Concerned with Mite Immigration?

Query:  Did mite immigration Correlate with Robbing at My Location?

Earlier on this sequence I identified that though wholesome colonies could rob mite-infested colonies in the event that they comprise ripening nectar on the time of their collapse, that didn’t occur right here.  We had positioned scales beneath each our Donor and Receiver hives to be able to see whether or not the Donors misplaced weight throughout collapse (which might point out that they had been being robbed), or whether or not the Receivers gained weight throughout our dearth (indicating that they’d robbed a collapsing colony) (Figures 7-9).

Fig. 7. An instance of what I appeared for ― a Donor shedding pounds on the similar time {that a} Receiver was gaining it.  I’ve aligned these two snips by date, to indicate D8 shedding pounds whereas R4 gained it.  However wanting again to Determine 5, one can see that R4 exhibited minimal mite immigration throughout that point interval.  So even when it was robbing, it wasn’t bringing again mites.

Fig. 8. A screenshot of scale information for the Donors [[1]].The one sudden weight losses that we noticed had been for Donor D6 and D8 (not proven on this chart) ― the remainder of the Donors confirmed no indication of getting robbed throughout their collapse.   However the bulk of these weight reductions could nicely have merely represented the physique mass of the employees that deserted the hive (the bees protecting 8 combs weigh roughly 4 kilos).


Fig. 9. A screenshot of typical scale information for the Receivers, with weight positive factors by R4 and R7.

Dialogue on Robbing

In my arid local weather ― by which there isn’t a considerable nectar stream in late summer time — we noticed no indication of weight reduction because of robbing happening because the Donors collapsed, nor any considerable weight positive factors to recommend that the Receivers had been robbing different colonies.

This isn’t to say that mite immigration can’t even be related to robbing in areas by which robbing does happen as colonies collapse, akin to the place nectar is ripening within the hive at time of collapse.

Even in these areas, precise area information indicating that robbing is extra of an element than is drifting, is (thus far) largely circumstantial.  Though it “is smart” that mites would exhibit a habits to hop on robbing bees for a experience to a brand new host colony, one factor that I’ve came upon through the years is that simply because one thing “is smart” to the human thoughts, that doesn’t essentially imply that it truly takes place with honey bees.  So let’s check out the proof.

Ever since Del Piccolo [[2]] reported that mites “most well-liked” nurse bees over pollen foragers, apparently because of variations of their cuticular hydrocarbons, it’s been fairly nicely established that there’s profit for a mite to discover a nurse bee to feed upon (reviewed by Xie [[3]]).  My very own testing [[4]] confirmed that non-flying (presumably younger) employees usually exhibit greater infestation charges than do flying employees sampled from the identical comb.

However Cervo [[5]], found (by way of GC-MS) that because the varroa infestation price of a colony elevated, the distinction in odor between nurse bees and foragers disappeared, as did the desire of mites for nurses over foragers (as decided by host-preference checks in petri dishes).  That discovering would recommend that the mite infestation price of foragers, relative to that of the nurse bees, would enhance because the infestation price grew — thus leading to a bigger variety of mites on the older employees drifting from highly-infested colonies.

However what occurs within the case of foragers from low-mite colonies robbing out high-mite colonies?  Peck and Seeley [[6]] noticed a circumstantial connection, main us to wonder if the mites in dying colonies acknowledge the robbers as being “international,” after which hop onto them to be able to catch a experience out of their sinking ship (this could make “complete sense” since it will help in horizontal transmission).  However alas, Cervo’s findings don’t help that speculation — they discovered that mites “didn’t present any desire between homocolonial and heterocolonial foragers at any mite abundance of the colony.”

And in maybe the one examine by which mite ranges on returning foragers had been quantified, DeGrandi-Hoffman [[7]] discovered that:

We didn’t detect excessive proportions of [foragers with mites] throughout any sampling interval as can be anticipated if foragers had been robbing closely infested collapsing colonies. Although will increase in mite numbers because of robbing in all probability happen, our information recommend different doable explanations for surprising progress in mite populations. [Foragers with mites] comprised at most 2–3 % of all of the foragers we captured in a sampling interval.

DeGrandi-Hoffman’s examine happened in Tucson, Arizona, the place there are late-season nectar flows [[8]], so it’s not clear whether or not robbing was happening.  I encourage additional analysis to discover the precise quantity of mite switch that takes place because of robbing!

Subject Research Wrap Up

The climate lastly turned chilly in late November (Determine 10).

Fig. 10.  Ambient temperatures remained excessive nicely into November

This gave me an opportunity to verify that our Receivers had been nonetheless mite free.  We took our final two stickyboard counts on 26 and 30 November, through the interim by which it lastly acquired chilly (and wet) sufficient to stop bee flight (and thus mite immigration because of robbing or drifting bees).  The stickyboard counts on the 26th had been 9,,6,1,2,8,5,2,4,14,7,10,2.  By the 30th they’d dropped to 0,1,0,0,3,0,0,0,0,0,1,0.  Once more, sturdy proof that the Receivers weren’t producing their very own mites.

I additionally checked the Donors—all had been devoid of bees, apart from D4, D5, D7, and D8, which had tiny clusters just below the lid.  And I solely noticed a single remaining tagged bee (in D8).  With that, I wrapped up the examine.


So what are the take-homes from our examine?

  1. I arrange this trial to find out whether or not the late-season enhance in mite infestation charges in our hives may very well be due from the drifting of bees from infested colonies exterior our apiary. We discovered that there could be substantial bee drift into hives a ½ mile distant, and a few drift to colonies a full mile away. Thus we now have onerous proof to help simply how vital it’s to encourage your neighbors to handle varroa of their colonies!
  2. We counted practically 3000 apparently-immigrated mites from our Receiver hives ― a median of 245 mites per hive. These immigrated mites weren’t evenly distributed, however even within the hives receiving probably the most mites, these immigrated mites would solely have elevated the infestation charges of these colonies by about 1% (3 mites per half cup of bees).  So even with 9 colonies collapsing on this apiary, we may hardly blame any giant will increase in mite wash counts within the surrounding colonies solely upon mite immigration from different hives.
  3. Different analysis has proven {that a} substantial proportion of employees could drift between hives in closely-spaced apiaries. On this trial we all know from recovered tags that a minimum of 4% of the bees we tagged drifted into the 21 hives that we monitored, however since there have been additionally unmonitored hives within the space, that 4% determine is clearly an underestimate of the entire quantity of out-drifting that really happened. Based mostly upon the sturdy correlation between tag restoration and mite drop, there’s cause to suspect that our sporadic tagging of bees (in an try to coincide with collapse), doubtless underestimated the true diploma of drifting of mite-infested bees that really occurred.
  4. There was way more drift to distant colonies than can be anticipated by probability. This discovering is totally opposite to “frequent sense,” and reveals how little we perceive how and why bees drift. It additionally brings into query suggestions relating to the spacing of hives in an apiary to cut back drifting.
  5. There was a persistently giant variation in mite immigration between hives that had been side-by-side at varied distances from the Donors, indicating that some colonies look like extra (or much less) engaging to (or keen to just accept) drifting bees than others (though the quantity of mite immigration didn’t essentially correlate with the quantity of entered drifted tagged bees).
  6. We noticed that probably the most intense mite immigration into the Receivers happened when the Donor colonies had been at their highest infestation charges (and likewise collapsing). It’s not clear whether or not mite immigration was primarily the results of infested employees abandoning colonies and in search of out different hives as they collapse (the “Mite Bomb” speculation), or merely because of the continuous mite diffusion related to “regular” bidirectional bee drifting.
  7. In the environment, with out a substantial nectar stream occurring through the examine, the collapsing colonies didn’t get instantly robbed, and there was no correlation between weight acquire (indicating robbing) and mite immigration.

Replace August 2023:  I introduced quite a few colonies with very excessive mite counts (30-70 mites per half cup of bees) to my residence yard to be able to harvest stay mites from them for my research.  To my dismay, quite a few them acquired robbed out as their populations had been collapsing.  Since I used to be inspecting the colonies frequently, I used to be capable of intently watch the method of collapse after which robbing.

As soon as a colony reaches the DWV “tip level” (mite counts round 50 or above), its quantity of brood begins to lower, and the employee inhabitants begins to break down quickly (by as much as two frames of bees per day).  And as soon as the cluster can barely cowl three frames, in a crowded yard, robbing strain can turn out to be an excessive amount of (remoted colonies with solely a handful of employees are capable of defend themselves in my space).  As soon as robbing begins, it explodes!  No noticeable robbing within the morning, however inside an hour of when it begins, the hive is mobbed by robbers.  Though the colony’s employees valiantly try to repel the robbers, they get overwhelmed, and a double-deep hive is usually “cleaned out” of honey inside a day or two. 

The Aftermath

Once I examine the hive instantly after robbing ceases, the combs are devoid of honey, and far of the brood has disappeared.  There are useless bees on the underside board, however I have no idea whether or not they had been defenders or robbers.  However there’s typically a remaining reformed cluster of stay, hungry bees – they don’t essentially die or drift away.  That cluster could signify a considerable proportion of the employees current previous to the initiation of robbing.

I used to be curious this morning once I inspected a colony that had been robbed out over the previous two days, whether or not the remaining bees had given up their mites to the robbers.  As a lot as I hated to sacrifice these poor survivors, I took a pattern of a half cup of them and washed the mites off them.

There have been too many to depend in a pile, so I divided them up and counted them twice.  There have been 117 mites on these roughly 315 bees!  It seems that their mites had not hopped off on the robbers to any extent, since my mite wash depend from the identical colony a number of days earlier had been solely 44. 

Subsequent Month

My function for enterprise this examine was to reply my query “Are the seemingly-rapid spikes in our mite wash counts in late summer time primarily because of the immigration of mites from different hives?”  That explanatory speculation is extraordinarily engaging, because it places the blame on another person, fairly than on one’s personal insufficient varroa administration.  However I’m undecided that it holds water.  Subsequent month we’ll take a look at extra onerous information, and run some simulations.



Thanks once more to my helpers Brion and Alice Dunbar, Sandy Honigsberg, Anna Mudd, and Brooke Molina.  And to Dr. David Peck for reviewing my information.

Citations and Notes

[1] Resulting from unfamiliarity with information preservation for the size hives, we misplaced all our uncooked information after we eliminated the batteries from the scales on the finish of the trial.  Fortunately, I had been following the burden information through the course of the trial, and had taken a number of screenshots.  I absolutely anticipated to see proof of robbing correlating with mite immigration, however didn’t.

[2] Del Piccolo, F, et al (2010) Collection of Apis mellifera employees by the parasitic mite Varroa destructor utilizing host cuticular hydrocarbons. Parasitology 137(6): 967-973.

[3] Xie, X, Z Huang, & Z Zeng (2016). Why do Varroa mites want nurse bees? Scientific Reviews 6(1): 1-6.

[4] https://scientificbeekeeping.com/re-evaluating-varroa-monitoring-part-4/

[5] Cervo, R, et al (2014). Excessive Varroa mite abundance influences chemical profiles of employee bees and mite–host preferences. Journal of Experimental Biology 217(17): 2998-3001.

[6] Peck, D & T Seeley (2019). Mite bombs or robber lures? The roles of drifting and robbing in Varroa destructor transmission from collapsing honey bee colonies to their neighbors. PloS one14(6), e0218392.

[7] DeGrandi-Hoffman, G, et al (2016) Inhabitants progress of Varroa destructor (Acari: Varroidae) in honey bee colonies is affected by the variety of foragers with mites. Experimental and Utilized Acarology 69(1): 21-34.

[8] Nightingale, J, et al (2008) Assessing honey bee equilibrium vary and forage provide utilizing satelite-derived phenology. In IGARSS 2008-2008 IEEE Worldwide Geoscience and Distant Sensing Symposium (Vol. 3, pp. III-763). IEEE.


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