Tag Archives: disease

Survival of the fattest

Winter bees have high levels of vitellogenin, a glycolipoprotein 1, deposited in their fat bodies which act as a food reservoir for the long winter.

These fat winter bees are essential for the successful overwintering of the colony.

Last week I discussed the major points that need attention for overwintering i.e. strong, healthy colonies with ample food in a weathertight hive.

This week I want to explore the relationship between colony strength, health – specifically with regard to Varroa and deformed wing virus (DWV) – and isolation starvation.

Isolation starvation describes the phenomenon where a small colony of tightly clustered honey bees gets isolated from the honey stores laid down in autumn, resulting – typically during protracted cold periods – in the colony starving to death.

Isolation starvation ...

Isolation starvation …

It’s both a pathetic and distressing sight. Bees, with their heads crammed into the bottom of cells searching for food, dying from starvation when literally inches away from capped stores.

Deaths and births

In temperate climates the winter is characterised by low temperatures and little or no forage for the bees. The queen usually stops laying sometime in autumn and starts again around the turn of the year. During the intervening period she may lay intermittently, but generally in limited amounts.

The fat bodied winter bees that are reared in late summer and early autumn are long-lived (about 6 months) and are responsible for getting the colony through the winter. They protect the queen, thermoregulate the hive and they help rear the brood raised in the autumn and through the winter.

In their absence – or if there are just too few of them – the colony will perish.

Winter bees do not all live for 6 months. The usual figure quoted is ~175 days 2. Some live shorter lives, some longer … up to 9 months under certain conditions.

Importantly, in studies I’ve discussed at length previously, high levels of DWV reduces the lifespan of winter bees. We know this because, in Varroa-infested colonies, researchers 3 have shown that the winter bees die off faster 4.

Live fast, die young

Winter bees with high levels of DWV don’t really live fast … but they do die young. In the studies above the average lifespan of winter bees was reduced by 20% in the colonies that died overwinter.

There are a couple of important things to note here. Dainat and colleagues were not looking at bees in the presence or absence of Varroa, or in the presence or absence of high or low levels of DWV. They simply looked at hives that succumbed in the winter or that survived, then measured DWV and Varroa levels. It’s a subtle but important difference. Their surviving colonies still had Varroa and DWV.

From analysis of hives that died or survived, and having marked known numbers of bees in late summer, they could determine the life expectancy of workers – in their surviving colonies it was ~88 days, in those that died it was ~71 days.

Healthy colonies

The gradual death of bees through the winter coupled with the reduced lifespan of winter bees with high levels of DWV explains why colonies need to be strong and healthy.

The following graphs are based upon modelled data 5, but show the influence of colony size and winter bee lifespan.

The first graph – the least important – simply shows the lifespan of bees. The graph plots the number of bees (on the vertical axis) in a population that die at a particular time (on the horizontal axis) after the start of the experiment. The blue bees have a longer average lifespan than the red bees 6.

Lifespan of winter bees

Lifespan of winter bees

In the following graphs remember that the blue bees are healthy, with low levels of Varroa and – consequently – low levels of DWV. The red bees are unhealthy and have high levels of Varroa and DWV.

Using this lifespan data we can look at the influence on the total number of winter bees in a colony (on the vertical axis) over time (horizontal). Imagine that the horizontal axis is the long, dark, wet and cold months of winter. Starting in early September and running through until late March.

Brrrr 🙁

Winter bee numbers in healthy (blue) and unhealthy (red) colonies

Winter bee numbers in healthy (blue) and unhealthy (red) colonies

It is clear, and of course entirely predictable, that the numbers of bees in the healthy (blue) colony are higher than those in the unhealthy colony at each time point. If the average lifespan is reduced (by disease) more bees will have died by a particular time point when compared with a healthy colony at the same timepoint.

Finally, consider that the shaded section of the graph represents the lower limit of bee numbers for viability. If the number of bees in the colony drops into this region the colony will perish.

Simplistically – and in reality – starting with similar numbers of bees a healthy colony will survive longer than an unhealthy colony.

Strong colonies

Using a similar approach we can also look at the influence of the average lifespan of winter bees on the survival of strong or weak colonies.

The following graph shows the numbers of bees in the colony over time for a strong colony (solid line) and a weak colony (dashed line) where worker bee lifespan is identical 7.

Winter bee numbers in strong and weak colonies.

Winter bee numbers in large (strong) and small (weak) colonies with the same average lifespan.

The shaded section of the graph again represents colony oblivion.

Large (strong) colonies take longer to drop below the threshold for viability and so – all other things being equal – will survive longer 8.

Mix’n’match

A strong colony with high levels of Varroa and DWV might actually survive less well than a weak but healthy colony.

Strong unhealthy colonies might survive less well than weak healthy colonies.

Large unhealthy colonies might survive less well than small healthy colonies.

In this graph the weak but healthy colony drops below the ‘viability threshold’ after the strong but unhealthy colony 9.

Winter bees and brood rearing

This is modelled data, but it makes the point clearly. Large and/or healthy colonies retain more of the all-important winter bees and so survive longer.

Simples.

The differences might not appear marked. However, for convenience 10 I’ve omitted the influence of winter bee numbers on the ability of the colony to rear brood.

If there are more winter bees, the colony is able to thermoregulate the hive better. It’s therefore able to keep any brood present warm. It’s therefore able to rear more brood.

As a consequence, the differences in bee numbers between the large or small, or the healthy and unhealthy, colonies will be much more striking.

Critically 11 the strength of the colony coming out of the winter is often the rate-limiting determinant for spring build-up to exploit early season nectar flows. Weak colonies develop less well.

Isolation starvation

Finally, returning to that pathetic little cluster of starving bees in the image at the top of the page. What is the relationship between colony health, strength and isolation starvation?

It’s now time to dust off my weak-to-non-existent Powerpoint skills …

Isolation starvation schematic

Isolation starvation schematic

Again, it’s straightforward. A large (strong) overwintering colony (A above) only has to move a short distance to access stores in midwinter. In contrast, a small (weak) overwintering colony has to move much further.

Consequently, small colonies become isolated from their stores during long, cold periods when the colony is clustered.

Prediction

Many beekeepers will be familiar with isolation starvation of overwintering colonies.

Most would explain this in terms of “very cold weather and the cluster was unable to reach its stores”.

Some would explain this in terms of “the colony was far too small to reach the stores when clustered”.

Very few would explain this in terms of “the Varroa and DWV levels were too high because of poor disease management last autumn. Inevitably most of my winter bees died off early in the winter, leaving a very small cluster of bees that were unable to reach the stores..

I suspect the real cause of isolation starvation is probably disease … specifically poor management of Varroa levels and consequently high levels of DWV in the colony.


Colophon

Herbert Spencer

Herbert Spencer

Another post, another poor pun in the title. Survival of the fittest encapsulates the Darwinian evolutionary principle that the form of an organism that survives is the one able to leave the most copies of itself in future generations. Darwin didn’t actually use the term until the 5th edition (1869) of his book On the origin of the species. Instead, the phrase was first used by Herbert Spencer in 1864 after reading Darwin’s book. Whilst ‘survival of the fittest’ suggests natural selection, Spencer was also a proponent of the inheritance of acquired characteristics, Lamarckism.

An Inspector Calls

Hive inspections are the preventative maintenance of the beekeeping year. Conducted properly, they include all the necessary checks to ensure all is well now and will be until the next inspection.

Inspections are an essential part of beekeeping. Beekeepers who don’t conduct inspections probably won’t be beekeepers for long … the colony swarms, goes irretrievably queenless or succumbs to disease.

Or all three 🙁

Actually, there’s another reason … I suspect that beekeepers who don’t regularly inspect colonies are more interested doing something else. They’d prefer to be playing golf or building model railways or potholing. I covered this a few months ago when discussing beekeeping principles and practice.

Shouldn't you be inspecting your bees today?

Shouldn’t you be inspecting your bees today?

Their enthusiasm to properly manage their colonies that is, not potholing 😉

Preventative maintenance

The clue is in the name … the purpose of inspections are to maintain the colony in a productive state and to prevent things from happening that might stop this being achieved.

‘Productive’ usually means collecting nectar for honey 1, but could equally well refer to making lots of bees for nucleus colony production. Or, for that matter, maximising drone production to flood the area with good genes for queen mating.

Essentially you’re checking the colony to ensure it’s best able to do what you want it to do.

And, if there are signs that things are going awry, you’re putting in place the preventative measures that help avoid a partial or complete disaster.

Brace comb

Brace comb …

A beekeeping “disaster” … let’s keep things in perspective. Swarming, queenlessness, laying workers, robbing, wasps, disease, Varroa infestation, brace comb and all the rest.

Quick or thorough but probably not both

Inspections can either be quick or they can be thorough, but rarely both. The definition of the term ‘inspection’ means “looking narrowly into; careful scrutiny or survey; close or critical examination”.

Therefore, unless you’re only checking one thing, for example whether the queen cells are sealed in a queenright queen rearing colony, it’s likely that the inspection will take some time.

Cell bar frame with three day old queen cells, The Apiarist.

3 day old queen cells …

How long depends upon experience. It probably takes me ~12-15 minutes to go through a box thoroughly and I have a reasonable amount of experience and get quite a bit of practice 2. This is a snail’s pace when compared with commercial beekeepers who can conduct a pretty comprehensive inspection in ~4 minutes.

A beginning beekeeper might take significantly longer than 15 minutes to inspect a colony.

But speed is not the issue. 

Why conduct inspections?

The issue – in a routine inspection – is determining the answer to at least the following five key questions (paraphrased from Ted Hooper in his Guide to Bees and Honey):

  1. Has the colony sufficient room?
  2. Is the queen present and laying as expected?
  3. Is the colony building up as expected (early season)? Are there queen cells present (mid season)?
  4. Are there signs of disease?
  5. Has the colony sufficient stores?

All of which, done properly, takes a reasonable amount of time.

So that’s the Why? What about when and how should inspections be conducted? These need to be addressed before considering the questions above 3.

When?

There are several ‘when’ questions to be considered. When should you conduct the first inspection of the year? When – as in what sort of day – should you conduct the inspection? How frequently do the inspections need to be conducted?

Unless you’re looking very quickly in a hive for a specific reason inspections should only really be conducted when the exposed brood aren’t going to get chilled. This means you should choose a day when the temperature reaches at least the mid-teens (°C). ‘Shirtsleeve’ weather some call it.

This influences both the timing of the first inspection of the year and – particularly early or late in the season – the time of day that the inspection occurs. On the East coast of Scotland I did my first thorough inspection this year on the 19th of April. Last year – although the winter was nominally shorter and warmer – some hives weren’t inspected until early May because there was never a suitable day.

Lots of hive entrance activity …

Use your own judgement about whether the weather is suitable for early season inspections. The bees should be flying well. This is both an indication that the weather is good enough and reduces the hive population making the condition and amount of brood easier to determine.

Hive entrance activity ...

Hive entrance activity …

Don’t base your decision to inspect on reports you read on beekeeping discussion forums (fora?) about others with their hives bulging with brood. They may be beekeeping in a warmer part of the country. They might be in a different country altogether. It’s also worth remembering that there’s a well-documented tendency – as with online reviews – for contributors to over-exaggerate the positives (and negatives) 4.

I also wouldn’t bother inspecting on an unseasonably warm day very early in the year. It’s unlikely you’ll be able to deduce a whole lot about the state of the colony.

I’ve started, so I’ll finish …

The frequency of inspections is largely dictated by the development time of a queen bee, and to a lesser extent by the strength of nectar flow in your locality.

If a colony is going to swarm they first prepare one or several queen cells. These are capped around day 9 after the egg is laid. Once there are capped queen cells and suitable weather the colony is likely to swarm.

That means you need to inspect more frequently than every 9 days during the peak swarming period of the season – in Fife that’s an ~8 week period from early May late June. In warmer regions, or in years with atypical weather, regular inspections might have to start earlier and continue later.

Queen cells ...

Queen cells …

“Around 9 days” really means anything from 8 days, so a 7 day inspection cycle makes most sense. If a careful inspection one week fails to find evidence of queen cells being developed there’s no chance the colony can swarm for a further 7 days at least (because there are no queen cells that are sufficiently developed).

“fails to find evidence” means you have to inspect carefully. A small charged queen cup, with a day old larva and a bed of Royal Jelly will be capped 6 days later … then they’ll be off 🙂

Generally 5 a colony with a clipped queen will take a little longer to swarm, allowing intervals between inspections to be extended to up to 10 days.

However, don’t rely on this … I’ve seen them (er, mine) swarm earlier than this. Inevitably it’s you’re strongest colony and best honey producer 🙁

Relax, but don’t be complacent

Once the peak swarming season is over the frequency of inspections can be reduced. I’m usually on a two-week cycle by mid-July, with most colonies getting their last inspection in mid/late August. This coincides with the optimum time to start applying Varroa treatments to minimise exposure of winter bees to deformed wing virus.

However, remember that a strong colony can fill a super very quickly during a good nectar flow. Inspections are required to ensure the colony has enough space – for brood expansion and for stores.

How to inspect

We’re running out of space … I’ll deal with this in more detail in a future post (and link to it from here).

Essentially, because the goal is to check the state of the colony, you need to ensure that the inspection is conducted in a way that best allows you to determine this.

An agitated colony or one stirred up to be highly defensive makes inspections much harder. It’s therefore important to be as gentle as possible, to be calm and measured in your movements and to avoid jarring the colony.

Use the minimal amount of smoke possible, don’t wave your hands over the top of the frames and don’t crush bees.

And if it all goes pear-shaped, if despite your best efforts the colony gets really stroppy, if you kick a frame over on the ground, drop your hive tool into the open brood box or the smoker goes out at a critical moment 6 … close up the box and try again another day.

Swarm arriving at bait hive ...

Swarm arriving at bait hive …


Colophon

An Inspector Calls

An Inspector Calls

An Inspector Calls is a play by J.B. Priestley. Set in 1912 and first performed in the mid-1940’s, it involves a man – calling himself Inspector Goole – questioning a well-to-do family about the suicide of a working class woman, Eva Smith. Over three acts it is clear that, independently, all in the family are responsible for her exploitation, abandonment, social ruin and eventual death through poisoning. “Inspector Goole” leaves, but the secrets are now out. Subsequent checks with the police and the infirmary show there is no “Inspector Goole” or recent suicides. The play ends with a phone call from the police about the suspicious death of a young woman by poisoning …

Alistair Sim starred in the 1954 film version of the play, where the surname of the lead character was changed from Goole to Poole.

Principles and practice

There’s a high level of ‘churn’ amongst new beekeepers. Beekeeping is relatively easy and inexpensive to start. The principles of beekeeping appear straightforward. But large numbers of beginners give up after a season or two.

Here I argue that the colonies and hives some of these beginners abandon pose a threat to other beekeepers, sometimes for years …

A better appreciation of the commitment required to successfully practice the principles of beekeeping might increase the success rates of beginners, though it might also dissuade some from starting in the first place.

Save the bees, save humanity

Supermarket bees

Supermarket bees …

Bees are popular. You only need to visit the supermarket, spend time on the High Street or browse the web, to find bees or pollinators mentioned. The plight of the honey bee is extensively documented in the press. In places some of these references are little more than thinly-veiled adverts … there are any number of beers or ales that now include ‘local honey’ to support bees and beekeeping.

So, public awareness is high.

A good thing

In some ways this is a good thing. The public are aware that, for a variety of reasons, our honey bees (and other pollinators, but I’m going to restrict myself to honey bees for the remainder of this post) are facing real problems. Habitat destruction, monoculture, disease, farming practices, global warming, mobile phone masts, parasites, imports and – the current favourite – neonicotinoids, are all/solely (delete as appropriate) to blame for the problems faced by our cute little bees.

Monoculture ... beelicious ...

Monoculture … beelicious …

It’s a good thing because you might get to sell more local honey which, as a consequence, means you’ll look after your bees carefully and manage them to make more honey next year. It’s a good thing – and I’ll declare a vested interest here – because the Government is encouraged to spend money on research to discover what the real threats to honey bees are (hint, it’s probably not mobile phone masts). This money will also help develop ways to mitigate these threats in due course.

There are a lots of other reasons why it’s a good thing. People are designing bee-friendly gardens, they’re planting wild-flower meadows, they’re reducing pesticide usage and favouring biological control or other pest management techniques. Farmers are being encouraged to leave wide field margins or build beetle banks … and some might even be doing this.

Too much of a good thing?

Some people are so concerned about the plight of the honey bee they decide to do the obvious thing and buy a hive and bees for the bottom of their garden. Obvious, because they’ve increased the number of hives and they’ll be getting lots of delicious honey at the end of the summer.

Some attend a winter ‘start beekeeping’ course (or fully intend to next year, once they’ve kept bees for the current season). Some think they’ll be OK with generous offer of telephone support from the person who sold them a midsummer nuc.

Others do this without any training, without any advice and without anyone to mentor them. 

What could possibly go wrong?

These new beekeepers are certainly well-intentioned. They fully intend to help bees. They really think they’re going to help. They love the idea of their own local honey.

Unfortunately, although many might think they appreciate the basic principles of keeping bees, they know very little about the practice of beekeeping.

Principles

Actually, the principles of beekeeping are a little more complicated than buying a hive, dumping a nuc into it and harvesting the honey at the end of the season.

The bees need to be fed when there’s a dearth of nectar, or in preparation for winter. They need to be protected from pests and diseases. They need space to expand. They need to be monitored in case they’re thinking of swarming. If they are, action is needed. And all this needs to be regularly and repeatedly checked throughout the Spring and Summer.

In short, they need to be properly managed. This management is the practice of successful beekeeping.

Without proper management I’d argue that one of the biggest threats to bees and beekeeping is the unmanaged colony (or hive) lurking in the corner of a field.

Practice

It’s easy to overgeneralise here. The following paragraphs are really describing beekeepers in their first few seasons. Experienced beekeepers can modify their management practices to one that suits their bees, environment, climate and strategy. Bear with me.

Inspections need to start before colonies build up too strongly in the Spring. Queens should ideally be found and marked (and clipped in my view, but some prefer not to do this). Inspections continue at 7 day intervals until the swarming season is well and truly over.

Not 11 day intervals … not when “the weather is better than today”, not when “I get back from the  fortnight in Crete”, not when “I can be bothered” … and certainly not only when “the neighbour is angry about the swarm clustered on their garden swing”.

Inspections have to be conducted thoroughly and with a purpose. It’s not a cursory glance in the top of the box. There’s a reason you’re doing it, so do it well.

Inspections must be done even if it’s 32°C in the shade and you’re melting in your beesuit, when the bees are stroppy as the OSR has just gone over and there’s no nectar coming in, when the weather is (again) miserable and all 50,000 will be ‘at home’ (and possibly tetchy as well) and even if you think “surely they’ll be OK for another day or two?”.

They probably won’t.

Hard labour

Beekeeping is hard work. If you’re lucky and the supers are bulging full it can be backbreaking.

You have to work reasonably fast and carefully. Manage only one of these two and, for different reasons, inspections can become tiresome.

You will get stung, though not often if you’re fast and careful and if you have well-tempered bees.

It can be hot as hell in summer and you can get wet, miserable and cold at any time of the season.

Uh oh ... swarming ...

Uh oh … swarming …

It’s not only physically hard, it is also mentally hard. Not like quantum physics, but it still requires quite a bit of thought. Bees are not ‘fit and forget’.

Using a combination of observation, experience and knowledge (and perhaps a little inspired guesswork) you need to determine what’s going on in a forty litre box containing over 50,000 bees. Is there disease present? Is it one you can do anything about? Is it notifiable? Is the queen present and laying well? Is the colony thinking of swarming (hint, a dozen sealed cells is usually an indication the colony has swarmed, not that it’s thinking of swarming 😉 ). Do they have enough stores? Do they need more space?

You need to be prepared for disappointment (and have a contingency plan). Despite your best efforts the colony may swarm. An extended period of lousy summer weather prevents the new queen from getting mated properly. The colony dwindles, is too weak to defend itself and is robbed out by another colony. Any number of things can go wrong.

Bees are managed, not domesticated.

That’s the reality of beekeeping. That’s the practice that underlies the principle of just dumping a nuc of bees in a box in late April and harvesting pound after pound of golden honey in early September.

If only it were that simple!

Beeless “beekeepers”

I regularly meet people who ‘once kept bees’. I’m sure you do to. Further discussion often shows that they certainly once had bees, but that they failed to keep them.

The colony died, was robbed out, repeatedly swarmed, absconded or – much more frequently – these beekeephaders simply lost interest.

Often they aren’t actually sure what happened to the colony. Have you ever asked them?

Their initial enthusiasm was tempered a bit by the first couple of inspections. The colony was getting much bigger, much faster than their experience made them comfortable with. They got a bit frightened but wouldn’t actually admit that. They missed an inspection (or two) as they were in Crete for the family holiday. The colony swarmed. They’d read somewhere that the colony shouldn’t be disturbed for a month, so they didn’t. They remembered again three months later but were then too late for the autumn Varroa treatment. Have you got any fondant to spare? They’ll have another go next year.

Definitely.

It’s not unusual for these hives to be simply abandoned. You find them in the corners of fields or tucked up against the hedge in a large sprawling garden.

Out of sight and out of mind.

Forgotten, but not gone

Forgotten, but not gone …

The gift that keeps on giving

Sometimes the colony limps on for a season or two. More often though it expires in the winter. The hive may then be repopulated the following year by a swarm. They flourish, or more likely perish and are repopulated again. Even if mice move in for winter and wax moth trashes the comb they still attract swarms.

duunnn dunnn ...

duunnn dunnn …

There’s a dozen or more hives like this on private land I know of. Some local beekeepers visit every year or so to collect any swarms that have moved in. I can’t imagine the state of the comb … or the colonies they collect.

But (queue Jaws music … duunnn dunnn… duuuunnnn duun… duuunnnnnnnn dun dun dun dun dun dun dun dun dun dun dunnnnnnnnnnn dunnnn) these abandoned and unmanaged hives mainly provide a great opportunity for Varroa to flourish. Together with both the foul broods, Nosema and goodness knows what else.

The abandoned hives effectively act as bait hives, attracting swarms which become established feral colonies. Most will eventually be decimated by Varroa and its viral payload, but many will chuck out a swarm or two first, or drones that drift from colony to colony. Some will get robbed out as they collapse – perhaps by one of your strong colonies – leading to a huge infestation with phoretic mites carried by the returning robbers.

They’re like a 40 litre cedar version of Typhoid Mary.


† And my extensive market research suggests they are very delicious too 😉

‡ After all, there’s no time like the present to start and the sooner you buy and populate that lovely cedar hive, the faster honey bee colonies numbers will increase. But they will definitely attend the beekeeping course next winter. Absolutely!

Telephone support. Really?! Have you ever tried to give telephone advice to a new beekeeper who’s standing by an open hive, mobile clamped to their ear, desperately looking for eggs, or deciding whether the queen cells are capped or uncapped? I’ve tried … don’t bother. Grab the beesuit and get to the apiary 😉

There are others I know of and have access to. The entrances to these have miraculously become stuffed tight with grass, so preventing their repopulation. How did that happen? 😉

A poor analogy, but it makes the point. Typhoid Mary (Mary Mallon) was an Irish immigrant  New York cook in the early part of the 20th Century. She was also an asymptomatic carrier of typhoid, a bacterial infection. During the period 1900-07 she infected at least 51 people, three of whom died. Investigative epidemiology traced a series of typhoid fever outbreaks to places where Mary Mallon worked. She was named Typhoid Mary in a 1908 article in the Journal of the American Medical Association.

Mary Mallon

Mary Mallon

Mary Mallon refused to accept that she was infected, was forcibly incarcerated (quarantined) twice and eventually died after three decades of isolation. The analogy is poor because Mary Mallon appeared in good health, whereas these abandoned hives (and the bees they contain) are often pretty skanky. However, the term “like Typhoid Mary” is often used to indicate a source of repeated infection … which is spot on.

 

 

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Deformed Wing Virus

Deformed wing virus (DWV) is probably the most important viral pathogen of honeybees. In the presence of Varroa the virus is amplified to very high levels in the colony, resulting in newly emerged workers – those that survive long enough to emerge – exhibiting the classic symptoms familiar to most beekeepers. These include deformed or atrophied wings, a stunted abdomen, additional deformities or paralysis of appendages and (not visible) learning impairment. There is a clear association between high Varroa levels, high levels of DWV symptomatic bees and overwintering colony losses.

Classic DWV symptoms

Classic DWV symptoms

These images are of workers from a colony treated for a month with Apiguard to reduce mite numbers. Many bees remained with symptoms. I suspect the high levels of mites pre-treatment resulted in the amplification of virulent strains of DWV which continued to cause disease even after the mite numbers were reduced. This emphasises the need to monitor mite numbers and treat appropriately with Apiguard, oxalic acid or – during the season – other appropriate integrated pest management practices such as drone brood culling.

Worker with immature mite

Worker with immature mite …

DWV symptoms and mite

DWV symptoms and mite