Many beekeepers complain about sudden late-summer spikes of their varroa counts, blaming them on mites immigrating into their hives from different colonies within the neighborhood. When my sons and I suspected that this was going down in some our personal yards, I made a decision to run a subject research to search out out precisely what was taking place.

INTRODUCTION

It requires human transport to maneuver the varroa mite throughout geographical obstacles, however to the dismay of beekeepers, as soon as launched into a rustic, the mite can unfold quickly to all colonies within the area. This invasiveness is essentially because of the pure drift of bees, which additionally leads to the carrying of mites from hive to hive. I wrote about what was then identified about mite drift again within the spring of 2018, and counsel that should you’re on this topic that you simply first evaluation my two articles on the topic [[1]].

SO WAS ANOTHER FIELD STUDY ON MITE DRIFT JUSTIFIED?

To reply that query, let’s check out information from Ritter in Germany, taken again in 1987 [[2]]. The paper was in German, however value translating. Ritter arrange two separate apiaries of 16 mite-free colonies — one within the foothills of the Black Forest in an space with low colony density and the opposite within the Rhine plain with quite a few closely infested colonies in the setting, after which tracked the infestation charges of the bees and brood within the experimental hives over time. His outcomes confirmed that having heavily-infested colonies within the neighborhood could make a heckuva distinction (Determine 1).

Fig. 1. Of curiosity is how lengthy it took for the impact to indicate within the mite washes. At an infestation fee of 35%, that will be 110 mites in a wash of a half cup of bees! Aspect word: Again then the advice in Germany was to make use of gasoline for performing mite washes. I assume that they had been cautious with their people who smoke!

However was the above sudden spike within the infestation fee because of a sudden inflow of mites in September? Check out Determine 2.

Fig. 2. It seems that the affect of mite immigration truly began to happen lengthy earlier than September. The obvious “sudden” spike as indicated by mite washes might have truly been because of an exponential improve in mite emergence in September, right into a reducing variety of grownup bees within the hives. This will likely clarify why even beekeepers who’re monitoring through mite washes should get shocked!

Sensible utility: Ritter’s subject information actually means that mite immigration from different colonies within the neighborhood can have an effect on the speed of mite buildup in a single’s personal hives. So I wished to dive deeper.

As a way to higher perceive this phenomenon, I modified my mite mannequin [[3]] to run some simulations (after first confirming that the mannequin might produce leads to the ballpark of Ritter’s information). Let’s first check out the estimations of particulars of varroa buildup over time in an untreated colony headed in direction of collapse in October (Determine 3).

Fig. 3. Permit me to make use of the simulation above to introduce you to the idea of the “Mite Manufacturing unit.” I added further plots for each day quantity of mite improve, in addition to for the estimated quantity of mite exodus on outgoing bees. Learn under for explanations.

By the point an untreated, nonresistant Mite Manufacturing unit about to break down:

It’s going to usually comprise round 15,000 mites in whole.
The above quantity can be rising at a internet improve of about 150 mites per day.
And because of the quick lifespan of summer season bees, above that quantity, there’ll probably be over 150 mites hitching a last trip out of the colony every day [[4]].

Sadly, there are too many variables for the mannequin to foretell the variety of these exiting mites fortunate sufficient to be carried to a different hive. With the above figures in thoughts, you could be questioning:

Sensible query: What affect may a Varroa Manufacturing unit within the neighborhood have upon my well-managed (handled) hives?

To reply that query, let’s run the identical simulation, however this time with a few efficacious therapies (Determine 4).

Fig. 4. Identical simulation, however this time handled in April and August, leading to a far decrease mite stage in mid-September (round 35). This now offers us two baseline numbers (15,000 and 35) to play with.

Now think about a neighborhood wherein one out of each ten hives is untreated, whereas the opposite 9 colonies are handled (every containing a median of solely 35 mites, as within the second simulation). Let’s see what occurs if an arbitrary 10% of the 15,000 mites within the untreated colony in some way handle to evenly “diffuse” (through bee drift) into the 9 different handled hives (a median of 165 mites per hive)(Determine 5).

Fig. 5. A single “Mite Manufacturing unit” has the potential to noticeably reinfest all the opposite hives within the neighborhood after their mid-August remedy (in actuality, the distribution of mites would in fact be uneven, with some colonies receiving extra mites than others). Think about the impact in case your apiary was surrounded by various “mite factories”!

OK, so mite immigration might clearly have a noticeable affect should you already had your mites effectively underneath management, however what should you had been working slightly behind the curve? (Determine 6).

Fig.6. On this simulation of fairly-typical colony administration, the efficacy of the April remedy was solely so-so (because of a lot of the mites being within the brood). After which the beekeeper hadn’t gotten round to giving an August remedy. Going into September, the simulated colony reveals a mite wash depend of 16 — which might be typical of “common” administration practices [[5]]. However the mite inhabitants in that hive would quickly exceed 5000, which means that an immigration of the identical 165 mites as within the earlier state of affairs could be solely a drop within the bucket!

Sensible utility: When you’re not staying on high of varroa all season lengthy, it might be a stretch in charge a late-season spike in mite counts upon mite immigration from elsewhere.

It seems as if mite immigration might certainly be a problem for these making the hassle to keep up low mite counts. So I felt {that a} subject research to raised perceive mite immigration in my operation was justified!

BACKGROUND RESEARCH

The very first thing I wish to do when designing a analysis mission is to search out out what’s already identified. For this text, I’ll snip some quotes (with minor paraphrasing and added emphasis) from related publications.

The second factor is then decide the particular questions that I wish to attempt to reply — these can be my research targets (which I’ll checklist under).

THE BIOLOGY BEHIND MITE TRANSFER BETWEEN HIVES

Varroa is a really profitable parasite, quickly reproducing in its personal host honey bee colony. However for the parasite’s continued success, bloodlines of the mite should in some way “horizontally switch” to different host colonies previous to the loss of life of their host colony.

To the mites’ nice benefit, they’re capable of make the most of bees exiting their host colony as an unwitting supply service that takes them straight into different colonies inside flight vary. This hitchhiking not solely permits varroa to infest newly-established colonies, but in addition to combine their genes amongst neighboring host colonies (which helps the mite to evolve).

HOW MUCH MITE IMMIGRATION ACTUALLY OCCURS?

It takes solely a single fertile feminine mite to begin an infestation in a colony. However beekeepers quickly observed that the diploma of mite immigration was generally rather more than that. Following Ritter’s publication, in 1988, German researchers Sakofski and Koeniger wrote a chapter known as “Pure switch of Varroa jacobsoni amongst honeybee colonies in autumn” [[6]]. And in 1990 [[7]] they once more confirmed that colonies from which varroa had been eradicated by remedy may very well be reinvaded by the mite, particularly throughout late summer season and fall. After which in 1992Greatti [[8]] revealed information indicating beautiful quantities of mite invasion going down in his monitored colonies in Italy. These findings had been adopted by different analysis, notably that of Frey [[9]], who discovered that mites might drift for a substantial distance. I’ve summarize the above research outcomes beforehand [[10]], however would they apply to my areas in California?

Sensible utility: There’s little question that mite migration between colonies can happen, and that it may be substantial. The questions for beekeepers then are precisely how and why it happens, how a lot immigration a colony can truly obtain, and is there something that we will do to scale back it.

Examine Goal #1: To find out the quantity of mite immigration that truly takes place in late summer season and fall the place I maintain my bees.

Examine Goal #2: To find out whether or not that mite immigration is regular or episodic.

Examine Goal #3: To find out whether or not all hives endure equally from mite immigration, or whether or not some are extra engaging or receptive than others.

HOW DO THE MITES GET TRANSFERRED?

Because the mites depend on bees to hold them to different colonies, it’s vital to grasp this facet. Greatti [[11]] listed the three essential strategies by which the mite manages to disperse from one colony to a different:

By the drifting of drones, that are identified to float freely between hives.
By the drifting of employee bees — which can are likely to “diffuse” mites from colonies with excessive infestation to these with low infestation.
By the robbing of colonies weakened by heavy infestation.

HOW IMPORTANT IS THE DRIFTING OF DRONES?

A latest research by Mortensen [^[12]] confirmed that drones do carry mites. It’s well-known that drones are likely to drift to different hives. That stated, Greatti, together with quantifying the precise quantity of mite immigration that might happen, examined whether or not putting drone excluders over the entrances of colonies would cut back immigration. He discovered that it didn’t.

Sensible utility: Though drones do loads of drifting, they could not contribute a lot to mite drift, and since there are only a few drones in our colonies in late summer season, I didn’t pursue the drone issue.

HOW MUCH DRIFT IS THERE OF WORKER BEES?

There have been loads of research indicating that there will be appreciable drift of employee bees, particularly in crowded apiaries, the place greater than half the employees in a colony might drift at a while of their lives to different hives [[13]].

However how concerning the comparatively sudden disappearance of the bees from a hive because it collapses from the varroa-virus complicated. Do these bees simply “disappear,” or do they wind up in different colonies?

Examine Goal #4: To find out the proportion of staff that drift from collapsing colonies into different hives.

HOW IMPORTANT ARE THE GUARD BEES?

There’s one other facet of employee drift apart from bees simply getting misplaced — to enter a international hive, they first must get previous the guards. Since I’ve lengthy chosen for “light” inventory, I’ve questioned whether or not I’ve additionally been inadvertently deciding on for bloodlines whose guards could be extra permissive to drifted bees making an attempt to enter their hive (Determine 7).

Fig. 7. Though we breed for gentleness, I typically observe guards doing a very good job at defending the doorway in opposition to intruders.

In 2017 Bordier [[14]] used video cameras to trace tagged bees on the entrances of monitored hives (Determine 8).

Fig. 8. I visited the INRA analysis facility in 2018, and snapped this image of one of many video entrance monitoring items that they had been utilizing.

Bordier concluded that (I’ve boldfaced the highlights):

Drifting habits is a consequence of orientation errors, and likewise depends upon the acceptance stage of the brand new host colony… adjustments in drifting depth are probably the results of a rise in colony acceptance. In regular situations, solely 3.5 % of incoming bees are checked by guard bees, however this permissiveness adjustments in response to season, density of bees and nectar and pollen sources— the acceptance ranges of colonies improve when nectar circulation is considerable however lower throughout dearth durations.

Sensible utility: So I’m nonetheless not clear on the significance of the guards in stopping mite immigration. Of curiosity is the discovering by Cappa [[15]] that guard bees mount a better protection in opposition to drifting bees which have been parasitized by a mite (how a lot may this play into “mite resistance” of a colony?). Distinction that discovering to that of Geffre [[16]], who “discovered that IAPV-inoculated bees had been considerably extra more likely to be accepted by the guards on the colony entrance than had been…controls.”

We clearly nonetheless have a lot to find out about guarding and drifting. I arrange my research in order that we’d solely get better drifted bees that made it previous the guards on the touchdown board.

DO MITES AND VIRUSES CAUSE INCREASED DRIFTING?

It’s well-known to biologists that any variety of parasites can change the behaviors of their hosts with the intention to impact higher transmission [[17]]. In order proposed by DeGrandi-Hoffman [[18]] in 2017:

We hypothesize that stress from parasitism and virus an infection mixed with results that viruses have on cognitive perform might contribute to forager drift and mite and virus dispersal.

So is there proof for elevated drift from colonies present process collapse? In 1991 Sakofski [[19]] discovered that:

By evaluating numbers of bees drifting from extremely infested and noninfested small colonies it may very well be proven that infested colonies drifted extra incessantly. The invasion of mites into bee colonies was monitored throughout a interval from spring to autumn. All colonies confirmed low values of mite inflow which elevated significantly on the finish of July and remained excessive till the start of October. Particular person values differed over large ranges that are more likely to be brought on by theft.

However in 2000, Neuman [[20]], though discovering substantial drift of staff and drones, did not discover a correlation between employee bee drift and varroa infestation

Goodwin [[21]] ran a subject trial in New Zealand wrote in 2006, wherein six of eight high-mite colonies with marked bees collapsed and received robbed out. Regardless of that:

The common share of bees drifting from untreated hives infested with varroa into neighboring handled hives didn’t exceed 3%. There have been no important variations between the proportion of drifting bees from the varroa-infested colonies and the handled colonies at any stage all through the trial. This means that the reinfestation of handled colonies doesn’t predominantly end result from heavy varroa infestations inflicting employee bees to float to different colonies, greater than they typically do in virtually varroa-free colonies.

After which in 2014 the premise that highly-infested bees had been predisposed to float was given wind by Cervo [[22]]:

At low mite abundance, mites keep throughout the colony the place they’re born and promote their copy by driving nurses. This desire ensures that mites are rapidly transferred to a different host larva throughout the similar colony the place they’ll reproduce. When mite abundance will increase throughout the colony, the dearth of variations in chemical cues between nurses and foragers most likely doesn’t enable mites to discriminate between bees with totally different duties and causes mites to trip on each of them…. by driving each nestmate foragers and international [robbers], mites improve their chance of leaving the exploited colonies. An infested colony, progressively weakened by parasites and mite-transmitted ailments, lastly turns into a straightforward goal for robbing foragers from international colonies; these robber international bees may characterize wonderful vectors to straight switch mites from the outdated exploited beehive to a brand new one.

This speculation instantly gained traction, and by 2017 the time period “Mite Bombs” was being thrown about, though with little supportive proof. And it was a foggy notion – not clearly differentiating the day-by-day “diffusive” mite drift from high-mite or collapsing colonies, versus the sudden and short-term direct switch of mites throughout robbing occasions that might happen through the collapse of a colony.

In 2017 Bordier [[23]] discovered that:

Roughly 10 % of our tracked bees drifted right into a international colony. The drifting prevalence was influenced by the colony’s location in house however not by N. ceranae parasitism.

There have been no important variations between the proportion of drifting bees from the varroa-infested colonies and the management colonies at any stage all through the research. This means that the reinfestation of handled colonies doesn’t predominantly end result from heavy varroa infestations inflicting employee bees to float to different colonies, greater than they typically do in virtually varroa-free colonies….The traditional stage of drift in apiaries will, nonetheless, unfold varroa from untreated to handled colonies.

And in 2019 Peck and Seeley [[24]] discovered that:

We noticed no indications that drifting of bees from the mite donor colonies into the mite receiver colonies elevated because the mite ranges within the mite donor colonies elevated.

Sensible utility: As engaging as a virus-induced improve in drifting habits speculation is, there are thus far conflicting findings (Determine 9).

Fig. 9. It’s simple to determine an unlucky employee that suffered from such a excessive an infection fee of DWV that its wings couldn’t develop. However you possibly can safely assume that each employee on this picture is contaminated with DWV to some extent, as evidenced by the dying brood. However does the varroa-DWV complicated trigger these contaminated bees to float at the next fee?

Examine Goal #5: To find out whether or not elevated varroa/virus ranges improve bee drift in my very own operation.

ROBBING VS. “ORDINARY” DRIFTING

We’ve now labored our method down as to whether mite immigration (a) is primarily because of the “odd” drift of bees from hive to hive (which I name “mite diffusion” for the reason that internet impact can be to maneuver mites from colonies with excessive mite focus to these with decrease focus), or (b) is principally from robbing bees carrying mites again from varroa-weakened hives. Such robbing may very well be surreptitious (and unnoticed by the beekeeper) or “overt” (simply noticed on the entrance when a collapsing colony will get mobbed by robbers) (Determine 10).

Fig. 10. The weird exercise on the entrance, coupled with the particles on the touchdown board signifies that this dwindled colony is getting robbed. I think that in our location, most mite immigration because of robbing could be from the surreptitious robbing that takes place throughout nectar flows, when there are few guards on the entrance.

Peck and Seeley [[25]] seemed into mite drift throughout robbing occasions going down in Ithaca, NY late within the season:

Our information additionally reveal that the colloquial terminology for [heavily infested] colonies—“mite bombs”—doesn’t precisely describe the mechanisms of intercolony mite transmission that we noticed on this research. We noticed no sudden “explosion” of mite-carrying bees from sick colonies to every of the wholesome colonies through employee drifting. Certainly, we discovered that few mites handed from the closely infested (MDC) colonies to the weakly infested (MRC) colonies by both employee drift (principally to close by colonies) or drone drift. It was solely when the MDCs had been weakened a lot that they turned irresistible robbing targets that mites handed in giant numbers from the MDCs to the MRCs.

Sensible utility: The mites in a colony that’s being robbed as it’s present process collapse (whereas there are nonetheless loads of stay mites within the hive) can actually hop onto the robbers (which the mites might simply acknowledge because of their totally different odor) and get carried again to the robbing colony. However such speedy robbing doesn’t happen in all landscapes — see my ancillary article on this challenge.

And at last, Kulhanek revealed a research final 12 months [[26]].

Extra bees from low mite colonies (n= 37) had been detected in receiver apiaries than bees from excessive mite colonies (n= 10). Receiver colony Varroa inhabitants progress was related to visitation by non-natal bees, however not excessive mite bees alone. Lastly, colonies missing robbing screens skilled sooner Varroa inhabitants progress than screened neighbors. Outcomes point out visiting non-natal bees might vector mites to receiver colonies. These outcomes don’t help the present two main theories concerning mite immigration – the “mite bomb” idea (bees from excessive mite colonies emigrating to collapsing colonies), or the “robbing” idea (natal robbing bees return residence with mites from collapsing colonies).

Sensible utility: Though mite drift throughout rob outs can certainly happen, it might be that mite diffusion because of odd bee drift could also be extra vital. Since robbing screens don’t stop colonies from robbing, Kulhanek’s findings counsel that they could scale back bee (and subsequently, mite) drift (teaser: I’ll quickly be publishing my very own testing of robbing screens).

Examine Goal #6: To find out whether or not mite immigration correlates with robbing.

There’s nonetheless another merchandise of curiosity…

HOW FAR CAN MITES HITCHIKE A RIDE?

A research by Frey in 2011 [[27]] had a shocking discovering — that mite drift just isn’t essentially a perform of distance, and that there will be appreciable drift even to colonies a mile distant.

Through the experimental interval, between 85 and 444 mites per colony had been launched into the receiver colonies. There have been no important variations within the invasion charges in relation to the space between donor and receiver colonies. In whole, 2,029 mites had been discovered within the 10 receiver colonies, however these solely correspond to 2.5% of the whole mite inhabitants within the donor colonies in the beginning of the experiment. Because of this the foremost a part of the preliminary V. destructor inhabitants died along with the collapsed host colonies…From a sensible perspective we might present that extremely infested honey bee colonies current a considerable danger to already handled colonies as much as distances of 1.5 km [roughly a mile] away.

Kulhanek [[28]] noticed substantial drift between hives in the identical yard, however her cameras noticed solely 47 marked bees (out of roughly 32,000 painted) drifting to receiver hives a half mile or additional distant.

Sensible utility: Frey’s discovering of the dearth of correlation between mite drift and distance was one thing that I wished to check in my residence yard.

Examine Goal #7: To find out the space that bees can drift from collapsing colonies.

Examine Goal #8: To find out how the speed of drift to close by hives compares to that to hives extra distant.

NEXT MONTH

Within the subsequent installment I’ll present we arrange our subject research with the intention to discover out the solutions to the listed targets. Keep tuned!

ACKNOWLEGEMENTS

Because of Peter Borst and Dianne Behnke for his or her help with discovering and scanning copies of outdated analysis papers.

CITATIONS AND NOTES

[1] The Varroa Downside: Bee Drift and Mite Dispersal, Components 16 a & b:

https://scientificbeekeeping.com/the-varroa-problem-part-16a/

https://scientificbeekeeping.com/the-varroa-problem-part-16b/

[2] Ritter, W., & E Leclercq (1987). Entwicklung der Bienen-und Varroa-population in Gebieten mit unterschiedlichen Möglichkeiten der Reinvasion. Tierärzt Umschau 42: 548-51.

[3] https://scientificbeekeeping.com/scibeeimages/Randys-Varroa-Mannequin-V2022-1-1.xlsx

[4] This determine is calculated from the calculated variety of non-returning grownup bees per day (because of growing older, getting misplaced, or different causes), assuming that they’re carrying mites at solely 2/3 the infestation fee of the employee bees on common).

[5] Kulhanek Okay, et al (2021) Survey-derived finest administration practices for yard beekeepers enhance colony well being and scale back mortality. PLoS ONE 16(1): e0245490.

[6] Sakofski, F & N Koeniger (1988) Pure switch of Varroa jacobsoni amongst honeybee colonies in autumn. In European Analysis on Varroatosis Management.

[7] Sakofski, F, N Koeniger, S Fuchs (1990). Seasonality of honey bee colony invasion by Varroa jacobsoniOud. Apidologie, 21(6), 547-550.

[8] Greatti, M, N Milani, F Nazzi (1992). Reinfestation of an acaricide-treated apiary by Varroa jacobsoniOud. Experimental & utilized acarology, 16(4), 279-286.

[9] Frey, E, H Schnell, P Rosenkranz (2011). Invasion of Varroa destructor mites into mite-free honey bee colonies underneath the managed situations of a navy coaching space. Journal of Apicultural Analysis, 50(2), 138-144.

[10] https://scientificbeekeeping.com/the-varroa-problem-part-16b/

[11] Greatti, M (1992) Op. cit.

[12] Mortensen, A, C Jack, J Ellis (2018). The invention of Varroa destructor on drone honey bees, Apis mellifera, at drone congregation areas. Parasitology Analysis 117(10): 3337-3339.

[13] Pfeiffer, Okay & Okay Crailsheim (1998). Drifting of honeybees. Insectes Sociaux 45(2): 151-167.

[14] Bordier, C, et al (2017) Ought to I keep or ought to I am going: honeybee drifting behaviour as a perform of parasitism. Apidologie 48(3): 286–297.

[15] Cappa, F, et al (2016) Bee guards detect international foragers with cuticular chemical profiles altered by phoretic varroa mites. Journal of Apicultural Analysis 55(3): 268-277.

[16] Geffre, A, et al (2020). Honey bee virus causes context-dependent adjustments in host social habits. Proceedings of the Nationwide Academy of Sciences, 117(19): 10406-10413.

[17] Poulin, R (2010) Parasite manipulation of host habits. Advances within the Examine of Conduct 41: 151-186.

[18] DeGrandi-Hoffman, G, F Ahumada, H Graham (2017). Are dispersal mechanisms altering the host–parasite relationship and rising the virulence of Varroa destructor (Mesostigmata: Varroidae) in managed honey bee (Hymenoptera: Apidae) colonies? Environmental Entomology 46(4): 737-746.

[19] Sakofski, F (1991) Quantitative investigations on switch of Varroa jacobsoni Oud. In Current analysis on bee pathology. Worldwide symposium of the Worldwide Federation of Beekeepers Associations, Gent (Belgium), 5-7 Sep 1990.

[20] Neumann, P, et al (2000) Colony analysis just isn’t affected by drifting and employee honeybees (Apis mellifera L.) at a efficiency testing apiary. Apidologie 31: 67–79.

[21] R M Goodwin, et al (2006) Drift of Varroa destructor-infested employee honey bees to neighbouring colonies. Journal of Apicultural Analysis 45(3): 155-156.

[22] Cervo, R, et al (2014) Excessive Varroa mite abundance influences chemical profiles of employee bees and mite-host preferences. J. Exp. Biol. 217: 2998– 3001.

[23] Bordier, C, (2017) Op. cit.

[24] Peck DT & TD Seeley (2019) Mite bombs or robber lures? The roles of drifting and robbing in Varroa destructortransmission from collapsing honey bee colonies to their neighbors. PLoS ONE 14(6): e0218392.

[25] Peck DT (2019) op. cit.

[26] Kulhanek, Okay, et al (2021) Accelerated Varroa destructor inhabitants progress in honey bee (Apis mellifera) colonies is related to visitation from non-natal bees. Scientific experiences, 11(1): 1-15.

[27] Frey, E (2011) Op. cit.

[28] Kulhanek, Okay (2021) op cit.

A Examine on Bee Drift and Mite Immigration: Half 1