# Robbing screens as an IPM tool lower mite loads



## Litsinger (Jun 14, 2018)

If the results from vanEngelsdorp et al are correct (and it appears the study was very robust in terms of design), this has rather significant implications for all of us, regardless of management approach. It would suggest that by simply installing robber screens on our colonies, we should expect a significant decrease the rate of mite population growth.

From the summary:

_'These results provide further evidence that mites transmitted between colonies and apiaries on drifting or visiting bees play an important role in driving mite population rates in some colonies. Of interest is that the data supported neither the mite bomb or robbing hypothesis currently suggested as the mechanism by which mites move between colonies. Rather, results suggest that a colony’s permissiveness predicts the rate of mite growth a colony will experience. This finding seems supported by the nascent understanding of the Varroa/virus complex and honey bee relationship, hinting at intriguing evolutionary questions regarding host parasite relationships at an individual bee and colony level. Arguably more impactful, however, was the finding that robbing screens, an inexpensive and accessible piece of bee equipment, could dramatically help beekeepers keep mite levels low. While more testing and refinement of this technology is necessary before its use is widely promoted, this offers some much needed hope for an industry struggling with damages caused by Varroa.' _


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## msl (Sep 6, 2016)

right, in the past it was felt it only stopped them from getting out, so (rather selfishly) it never caught on as it didn't help "you" just those around you..
Now if its shown to help "you" there will likely be more buy in..


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## GregB (Dec 26, 2017)

Basically it says - obstruction of the entrance is good.
And more generally, entrance defensiveness is good.

I will say *periodic *obstruction because (from my observation!) this triggers short-term elevated irritability and defensiveness at the entrances and around the hive.
My boy got stung up once by the freshly screened-in bees (formerly mild bees).

In time (as bees adjust), the entrance defensiveness declines.
1-2 weeks?

Basically, why I like the entrance paper tape-overs.
Similar effect.
Nothing to build.
Cheap and easy to (re)apply and entrance size adjusted by the bees to their need.


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## psm1212 (Feb 9, 2016)

Great find msl!. I have read the first couple of pages. Might not get back to it until the weekend, but looking forward to it. Thanks for posting.


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## Akademee (Apr 5, 2020)

This is great news, any idea if certain types of robbing screens are more effective than others? I know there is the big bolt-on type, but I use the entrance reducer with number 8 screen wrapped around it the moment I take honey off my hives.


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## RobPS (Jan 14, 2021)

New beekeeper here... I was advised to have entrance screens avail to prevent robber bees later in the season, and this article provides another great reason. My question as a newbie... and related to the comment above about hives becoming potentially more aggressive with them in place... Would it make sense to install the screen from the very beginning, when I first get my nuc and package (getting one of each for two hives total), so that they adjust to it from the start? 

Here is the entrance screen that I purchased:








Ultimate Universal IPM Robber Screen


Brought to you by Bee Smart this robbing screen works well on most 8- and 10-frame bottom boards. Cutting the screen down to fit correctly on some styles of bottom boards is needed. EZ installation with stainless push in pins. Great ventilation, UV protected. Ship wt. 1 lb. ea.




www.dadant.com


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## mtnmyke (Apr 27, 2017)

It certainly doesn't hurt to run a robbing screen all year. The main colony gets very used to it and comes and goes without an issue. They only work because robbers get in a frenzy and don't take the time to figure out where the entrance is, only dart toward where the smells are. As such, you could technically run them all year round with no ill effect, that I can see.

I've only found hives that are getting robbed to be defensive so maybe put on the robbing screen before that becomes an issue.


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## LAlldredge (Aug 16, 2018)

I 2nd the BeeSmart robbing screen. Considered standard equipment for me after an ugly 1st year event. This is just one of those no brainer pieces of equipment that eliminates a lot of issues. Will be putting them on after mouse guards come off.


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## LAlldredge (Aug 16, 2018)

RobPS said:


> New beekeeper here... I was advised to have entrance screens avail to prevent robber bees later in the season, and this article provides another great reason. My question as a newbie... and related to the comment above about hives becoming potentially more aggressive with them in place... Would it make sense to install the screen from the very beginning, when I first get my nuc and package (getting one of each for two hives total), so that they adjust to it from the start?
> 
> Here is the entrance screen that I purchased:
> 
> ...


You bought great robbing screens. I consider them standard equipment. Yes, I would install them immediately. I have not found any change to the hive mood from putting them on. Quite the contrary. You want to do everything you can to keep them calm and less stressed. Smoke used well, large flour sack cloths to drape over boxes, quiet box, well fed, mites treated etc. There are genetic differences that influence behavior plus times of the year when food is scarce. Show me a calm apiary and I'll show you a well thought out plan.


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## psm1212 (Feb 9, 2016)

RobPS said:


> Would it make sense to install the screen from the very beginning, when I first get my nuc and package (getting one of each for two hives total), so that they adjust to it from the start?[/URL]


I agree with mtnmike with two possible exceptions. One season I ran mating nucs in the late summer. They were getting picked on by some nearby colonies, so I made robbing screens for all of them (8 if I remember correctly). All 8 failed to return a mated queen.

Now, late summer can be a hard time anyway, and my mating nuc success rate is probably only 70% on a very good season. But I have always had in my mind that it was the robbing screens that confused the returning queens. Of course, I don't know that.

So if you know you have a hive that is trying to requeen itself, you might want to get that robbing screen off. 

Also, in the middle of a good nectar flow, I would not want to hinder my bees with having to negotiate a robbing screen. Additionally, no one is robbing during a good nectar flow. Would it make a substantial difference in honey yield? Your guess is as good as mine, but every time I drove by it I would wonder about it and torture myself with the possibility. Such is the state of my mind.

Otherwise, I don't see any harm in leaving it on year round.


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## GregB (Dec 26, 2017)

This robbing screen method is somewhat mis-leading and overly narrow approach (and in certain scenarios is outright bad - see mating nucs).

More general approach is to simply obstruct/limit the entrance using various techniques.
Methods include -

yes, the robbing screen;
small upper entrance (after years of using now now I am positive such entrance is always very active and well defended; works well for weak hives/small nucs/mating nucs)
frames configured in the warm way in conjunctions with the upper entrance (this is a hunch being tested out still - but I like what I have seen)
<.... probably more>
I would not go crazy and start doing the robbing screens right and left regardless of the circumstances.


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## lharder (Mar 21, 2015)

I put on robbing screens on my production hives as I harvest honey, late July /August and stay on till flight stops. Its good for me and the neighbors. I wish it was standard practice around here. The bees are in each others business and we should protect from failing hives where ever they are. They work, I can harvest honey from a failed hive late in the season.


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## Litsinger (Jun 14, 2018)

A little more background on this study (among others) in the August 2021 ABJ:


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## Struttinbuck (Mar 8, 2020)

Thanks for the post dude. Super good info.


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## GFWestTexas (Jul 10, 2021)

I like the reducer method, when I started out I had a belief that the stronger the hive the larger the entrance should be. However it didn’t take long to realize once I began doing cut outs that some huge hives have small entrances, and it does not hinder them in growth. I also began making my own reducers where entrances are in differing locations, as in larger yards robbing is often another colony in the same yard. Don’t get me wrong I also use robber screens, but differ entrance location on each one, as much as possible. I have found if all the entrances are in the same location, it doesn't take long for the bees to figure it out, this rendering it useless, unless the invaders are coming in from else where. This is a very interesting study, and I am enjoying the read.
Cody


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## Litsinger (Jun 14, 2018)

GFWestTexas said:


> However it didn’t take long to realize once I began doing cut outs that some huge hives have small entrances, and it does not hinder them in growth.


Cody: 

I'm with you on this one. While I accept that I might be missing out on some surplus gathering I am convinced that the smaller entrances help minimize passive robbing and also help in the battle with SHB- which I expect you have to deal with too.


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## GregB (Dec 26, 2017)

Here is a simple math that shows how the round entrance is more dependable vs. the compatible (in area) elongated entrance.
I wish someone did a study already.

Passive/quiet robbing usually occurs at the less defended ends of the elongated rectangular entrance where the robbers are trying to sneak inside.
Similarly, alien bees looking to join also are trying the same tactic.
At the same time a single guard bee needs to pay attention to longer perimeter with the elongated entrance.

So, I think simple math demonstrates how the round entrances are beneficial, especially to the smaller colonies.
Small round entrances even more so - a low tech and effective solution to a problem created by factory-made rectangular entrances.
At certain colony size this is no longer essential when the entrance congestion sets in.

Radius of the round entrance pictured - 1/2 inch.
Rectangular entrance has similar area and is 1/2 inch tall (for math convenience).
Notice how much more efficient is the round entrance in terms of the edge.


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## Gypsi (Mar 27, 2011)

Given the amount of fall robbing in Texas I usually have the entrances shut down small if not a robber screen. And I usually have a very low mite count


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## Litsinger (Jun 14, 2018)

GregV said:


> Here is a simple math that shows how the round entrance is more dependable vs. the compatible (in area) elongated entrance.


Makes good sense to me, Greg V. I've never found a bee tree with a rectangular opening. 😉


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## Litsinger (Jun 14, 2018)

Responding to criticisms of the experimental design and conclusions (highlighted emphasis mine):


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## GregB (Dec 26, 2017)

So since this robbing screen as a mitigation came up.....
Take a look at this picture and notice what is wrong with it.... 











What is visibly wrong with it:

weak test colonies - observe very low activity at the entrances
proportionally large entrances - which the weak test colonies are unable to plug up by the own traffic (let alone filter the aliens).
only two colonies are used this picture, NOT four, for unclear reason (hopefully honest mistake, not an attempt to make impression).
A strong colony compatible to a single deep Lang should look like this (two small round entrances in the picture). This is a good entrance density which is difficult for alien bees to infiltrate through.










Granted I don't know the exact time of day the pictures were taken (could very late/early in the day).
Still suspicious of a good experimental setup.
At least I would personally make better pictures to make a visual point.


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## Litsinger (Jun 14, 2018)

Thanks, Greg. I don't know if the previous post from the ABJ addresses all your objections, but I think the idea was to create a clear distinction in directionality- so relatively hard to enter the robbing screen-equipped colonies and relatively easy to enter the non-equipped colonies.


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## msl (Sep 6, 2016)

GregB said:


> This is a good entrance density which is difficult for alien bees to infiltrate through.


the entrances were quite small to alow the cameras to do its job









its not an infiltration, its not robing, they aren't sneaking in or pushing there way threw,.... its them being let in..
the suggestion is it has to do with the genetics
someing the UGO low varroa growth expemt is seeing as well, with low varroa gowth being linked with higher defensive behavior..


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## johno (Dec 4, 2011)

What troubles me about robbing screens on all hives to avoid drift is, are all robbing screens different, I was under the impression that if bees could figure out their own robbing screen they could certainly figure out the same kind of robbing screen on another hive.


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## GregB (Dec 26, 2017)

msl said:


> its not an infiltration, its not robing, they aren't sneaking in or pushing there way threw,.... its them being let in..


I get the point is about "being let in" (whatever it means from the bees point of view).

Still, for the fullness of this experiment, I would also add a section of hives with a little round entrances and the brood right behind the them (like the pictured) and see how many bees get let in different config. Just to be sure!
There are unconfirmed testimonies that this, in fact, matters.

Entrance is not only what is visible outside.
Entrance is also internal area immediately behind the hole and not easily visible.


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## Litsinger (Jun 14, 2018)

johno said:


> I was under the impression that if bees could figure out their own robbing screen they could certainly figure out the same kind of robbing screen on another hive.


Good question. It does beg for a more long-term evaluation of efficacy over time. From the research:

_'... screened colonies exhibited reduced Varroa population growth compared to unscreened colonies, suggesting that mites are not primarily being brought home on bees returning from robbing high mite colonies. Mites are more likely being transmitted to receiver colonies by non-natal bees, and visitation from any non-natal bee is correlated to accelerated Varroa population growth.

These results suggest the need for an alternative hypothesis, which is here referred to as colony permissiveness. Colonies that permit more presumably short term visiting bees experienced greater mite population growth than their less permissive counterparts. The term “visiting” is used here instead of robbing because robbing is typically characterized by mass recruitment of nest mates, so that many non-natal bees are stealing a colony’s resources together. Here, no evidence of recruitment was seen as the number of visitors to each receiver colony was low, thus the visitation behavior observed did not appear as true robbing. It is likely that bees from unmarked colonies were also visiting receiver colonies, and the number of marked visitors detected is probably a small fraction of the real number of non-natal bees visiting receiver colonies.'_

Ultimately, I think the key immediate take-away is as follows from the ABJ article:

_'Colonies with robbing screens had lower increases in mite loads during the study than unscreened colonies. We hypothesize that colonies that were easier to gain entrance to received more non-natal bees and thus received a higher influx of mites.'_


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## johno (Dec 4, 2011)

If you whole yard is covered with the same sort of plastic screen I would think that your own bees could still drift, however I will agree that strange bees from another yard may have difficulty entering you hives with screens. So I guess the lesson is screen all weak or crashing hives, the problem that I see there is that a beekeeper who is happy to let a hive crash is not going to bother adding a robbing screen.


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## Litsinger (Jun 14, 2018)

johno said:


> So I guess the lesson is screen all weak or crashing hives, the problem that I see there is that a beekeeper who is happy to let a hive crash is not going to bother adding a robbing screen.


True enough- but also suggests that if one has crashing colonies in their flight path, robbing screens added to one's own colonies will offer some defense against late season mite infiltration.


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## William Bagwell (Sep 4, 2019)

GregB said:


> Take a look at this picture and notice what is wrong with it....


Spotted the photo shop before reading your analysis. Also appears the robbing screen is upside down?


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## msl (Sep 6, 2016)

johno said:


> I was under the impression that if bees could figure out their own robbing screen they could certainly figure out the same kind of robbing screen on another hive.


well
as the story goes bees learn there entrance by leaveing threw it.. When they are trying to get in to a new hive they are using smell..
that said I haven't seen any empirical work on the effect so its just "they work" is "common knowledge" 

any way, its one study... like most thing you need to wait till repllates happen and there is a trend


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## Gray Goose (Sep 4, 2018)

Litsinger said:


> Responding to criticisms of the experimental design and conclusions (highlighted emphasis mine):


interesting test Russ
I wish math was given out in more detail.

Like mite counts went from X to Y in Z number of days.

Also suggests placing hives where drift cannot happen as much.
these were all white and in a row.

GG


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## msl (Sep 6, 2016)

Gray Goose said:


> Also suggests placing hives where drift cannot happen as much.
> these were all white and in a row.


the "drift" was coming from 1/2 to 1 mile away


> The donor apiary was placed near the geographic center of the farm. Four receiver apiaries were placed approximately 0.8 km (0.5 mi) from the donor apiary. Four additional receiver apiaries were placed approximately 1.6 km (1 mile) from the donor apiary (Fig. 1).














Gray Goose said:


> I wish math was given out in more detail.
> Like mite counts went from X to Y in Z number of days.


|



















> Sticky board mite counts (mean # of mites dropped per colony per day) in the first experimental week were significantly higher than any other week (first week 6.35 ± 0.98 vs. other weeks 1.71 ± 0.12, t = 4.69, df = 31.9, _p_ < 0.001). This is likely due to residual mite drop from the formic acid treatment that ended one day before sticky boards were placed on colonies


.


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## Litsinger (Jun 14, 2018)

Gray Goose said:


> Like mite counts went from X to Y in Z number of days.


It's in there, but you've got to dig down a bit- here is probably the best single figure:






Figure 15 | Scientific Reports







www.nature.com







Gray Goose said:


> Also suggests placing hives where drift cannot happen as much.


While they don't ever explicitly address it, I think the idea was to mimic typical apiary conditions. They note:

_Bees often drift between colonies, representing a potential route for Varroa transmission. Crowding of colonies within apiaries and throughout the landscape results in increased Varroa infestations as bees are more likely to move between colonies._

Here was their approach to where the screens were placed:

_Robbing screens were placed on 50% of receiver colonies. In each receiver apiary, one colony in the middle and one on the end of the row received a robbing screen (Mann Lake, Hackensack, MN). Robbing screens are metal mesh that block the regular colony entrance, and have a separate hidden entrance at the top of the screen. Only bees that live in the screened colony learn the new entrance, and the reduced entrance is easier for natal bees to defend, so non-natal bees are deterred from entering. Whether the left most or right most colony was screened was chosen randomly, but screening both end colonies was avoided, as unpublished data suggests that end colonies are more susceptible to receiving visiting bees (vanEngelsdorp Pennsylvania State Inspection records). After the first screened colony was randomly chosen, a second colony not adjacent to the screened colony received a robbing screen._


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## Gray Goose (Sep 4, 2018)

msl said:


> the "drift" was coming from 1/2 to 1 mile away
> 
> 
> 
> ...


thanks
I opened what I though was the study missed it.

GG


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## kilocharlie (Dec 27, 2010)

The most effective robbing screens I've found are tall ones - 6 to 7 inches tall with a privacy screen hiding where the bees go up to exit. This gives the home team enough time to get the jump on invading robbers, which are still zig-zagging into the screened portion of the device.

The hole has to be the right size - it has to let a lot of 17-day to18-day-old guard bees out in a hurry.


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## JustBees (Sep 7, 2021)

My robber screen, has gone through a few changes from the original that got thrown together because of robbing.
This is s total re-design paying attention to removing any obstacles, I had a tunnel branching off the main cavity behind the screen.
There were ridges and ledges that the bees ran into and turned back, and dead bees would collect as the undertakers had similar problems.
Now it is smooth, both the roof and floor can be followed to the exit with no obstructions.
Slightly down hill will help the undertakers drag out the dead.
The new design also has a ledge on the outside between the real enterance and the screen that will turn away robbers.
The screen is attached to the back of the front wall so the transition from screen to wood is smooth.
I added a ledge on the face above the landing board to direct lost bees towards the real entrance as they want to track upwards when they move sideways on the face.
3/8" x 2" opening. The hive itself has a downward sloping entrance 1/2" x 5" I have that reduced for winter (Blue Tape)


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## Litsinger (Jun 14, 2018)

Great short presentation by Dr. Kelly Kulhanek which offers some context and color to this important study:


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