by Dennis van Engelsdrop
As Kim mentioned, I’m part of the Bee Informed membership and we conduct the loss survey every year. We’ve done that now for 9 years. Five years ago, we switched that survey and we started talking about not just winter loss but summer loss and annual loss. What you can see, which is quite troubling is that our winter loss we had just over 35% (the yellow), has come down a little bit over the peaks we saw earlier. We look at our summer loss we see that that has now surpassed our winter loss. So now we’re in a situation where we lost more colonies between April and October than in between October and April. It’s astonishing because that’s the time when bees should thrive. There’s lots of good nourishment out there. It’s a great time for bees! So, it’s really troubling that we’re seeing these high losses in the summer. This is the annual loss of course. You could guess what the summer losses might be. We also ask beekeepers what they think is a reasonable loss over the last year. On average, beekeepers say that they should lose about 15% of their colonies. Could you imagine if a cow farmer said, “Oh yeah, I lost 15% of my cows over the course of the year and I’d be happy?” This is troubling because we’ve come to accept these very high rates of loss in our industry. I wonder whether we need to; if we need to think of what we consider acceptable rates of loss if they really are acceptable. Traditionally, before varroa mites, before the 1980s, people who lost 10% were too embarrassed to tell their neighbors and now we’re happy with 15%, in some cases. Certainly, there has been a big shift. As beekeepers, you know that this shift and this whole idea of colonies dying has really captured the public’s imagination. It’s meant that we have a lot of people, not necessarily beekeepers, who have really clear ideas on what is causing these losses. Very strong and clear ideas. I’m reminded of a saying from a Baltimore critic, “For every complex problem, there is an answer that is clear; that is simple; that is wrong.” The drivers of colony losses are complex. There are several different factors interplaying and playing off of each other and we have to remember that it’s broader than one issue.
Although, I’m mandated in this talk to talk about varroa. I certainly think that varroa is a major contributor to colony losses. I’d like to bring up some of the caveats. The first one is is that I recognize when I say I think varroa mites are the major cause of losses in the US, many people get annoyed by this. I’ve been a beekeeper for 30 years and I’m approaching this whole idea from the point of view of an epidemiologist, not someone who studies individuals but as someone who studies a population. It’s very true that people have lost colonies from poor nutrition and pesticides. I’m surprised at the level of varroa mite and how quickly we see varroa mite populations increase at the population level.
The other caveat is that a lot of the data I’m presenting is correlated data. And correlation is not the same as causation. If you want to find the best predictor of colony losses based on correlation, it’s actually the number of people who are arrested for Marijuana possession. So, it’s inversely proportionate. Now of course, when you see this statistic you all know there is nothing related and this is a fluke. This is not causation. There has to be a biological mechanism there. As sometimes things are co-variates; they’re co-related. For instance, there’s a very strong correlation between shark attacks and ice cream sales. That’s a very good, strong correlation again. But, that’s only because you swim in the summer, which is when you eat most of the ice cream that that correlation exists. I say this because a lot of the data I’m about to show throughout this study is correlative data. Now, the preponderance of evidence — once you’ve seen correlations year after year, over different populations, and in different situations — just on their own, they’re not experimental data; you need experimental data to justify it or you need a lot of other correlative studies to help. For instance, smoking. We have no experimental data that smoking’s bad for you. It’s all correlative.The reason for that is it would be unethical to cut this room in half and say “You guys smoke two packs a day and you guys don’t” and see what happens. Sometimes things aren’t set up to do good experiments with because they’re unethical or too costly. Correlation has a value but it’s not the be-all-end-all. There are four factors affecting colony health: parasites and pathogens, pesticides that farmers and beekeepers are applying to control varroa mite, poor nutrition because of monoculture habitat or the lack of good forage there, and management.
When we do the winter loss survey, we follow it up with a management survey. We ask beekeepers what they think is the major reason your colonies dies this past winter. Right away, the response differs between sub-groups of beekeepers: backyard beekeepers have very different responses than commercial beekeepers. Backyard beekeepers are people who have under 50 hives. Commercial beekeepers have over 500 hives. If we look at backyard beekeepers, they identify a poor winter as the major cause of loss, followed by starvation, and then weak colonies in the fall. These are all manageable conditions. However, if we look at commercial beekeepers, they identify queen failure, followed by varroa mite, and then pesticide as the leading three causes of losses. The queens and varroa mite interchange year by year, in terms of whether they’re ranked first or second, but clearly, varroa mites are identified by commercial beekeepers as being a problem. These are guys who are actively managing and they still recognize the problem with varroa mite. This is the silent monster in our midst. It is a very amazingly well-adapted parasite for bees. It’s really good at what it does, which is hang on to bees, move into root cells, and have more babies. We’ll look at its anatomical features and respect why it’s so good. The first thing you’ll notice is that it has this really hard shell. It’s a hard tic, in fact. Its hard shell keeps it from dehydrating. If you think of other mites, like honey bee tracheal mite, it has to live in the trachea of the bees and dries up really quickly and can’t stay out in the environment for too long. However these mites have a very thick shell, its exoskeleton, which allows them to survive outside of the hive, on the bottom board of the hive, or outside of the food chamber for extended periods of time.
Varroa Mite Biology
The varroa mite has all these sensory hairs but they also have a line of hard and nail-like hairs on the outside and that helps deter other bees from chewing on that mite. It deters rooming and it’s those sharp projectile spines that mites have. There’s also a wax coating that absorbs the smell of the colony, which acts as a chemical camouflage. It smells like a colony, which are really dark and humid. So now, the bees would rely on their sense of smell to get rid of intruders and now, it smells just like the colony and it adapts well to it because that wax is able to absorb the smell of the colony.
Looking at the feet of the mite, they’re a little bit different in the fact that they still have these claws to grab onto things but you’ll notice that they have all these little hairs here. Honeybees have a pad there, like a suction cup pad, which allows them to walk upside down. These mites use these hairs and in fact, these hairs are a lot like the hairs on a gecko’s feet. It creates this really large surface area so, it’s the attraction of molecules that keeps the mite able to walk on the vertical surface. It’s causing this huge surface area and so it’s molecular bonding occurs very weakly but because the mite is so light and because of that tremendous surface area, it’s able to crawl upside down or up the cone or sideways. It’s gotten very good at moving around both on the mite and away from the mite.
It also has a very special tube that allows it to breathe. One of the first things it does is when it enters a breed cell, it buries down into the brewed food, that pool of liquid food that the bees are breeding so this tube allows it breathe while it’s submerged in that surface. It’s adapted for that behavior as well. That really strong outer shell, its carcass, that exoskeleton is also really thin, which allows it slips between the plates on the abdomen of the bee and get right in there and feed between that soft tissue that connects the hard plates.
Now, I’m going to talk about how to make your own varroa treatments so you can control mites. It’s totally illegal and you can never repeat it! Of course, maybe a year or two ago if you were a commercial beekeeper and you were asking me what you should treat, I would tell you to call other commercial beekeepers. That’s because there were lots of different products that were a lot cheaper to make yourself and apply to the hive. Those days are over now. The only two products you can use don’t work anymore. Amitraz you can’t buy in a way that you can make your own product anymore that doesn’t have high levels of xylene in it or you have to smuggle it into the country. So there is no secret backyard recipe. What’s going to happen next? There certainly is research out there that may be suggestive and may be helpful the fact is that most of those products are years away. We’re stuck with what we have right now and we have to figure out how to use it most effectively and more efficiently in a way that’s going to sustain until these new products come out. So here I’m going to come up with the last little quote that there is no silver bullet and frankly, you don’t need one. It is far more important to “find the right kind of gun, load the gun, and most importantly, be able to figure out where the werewolf is.” Really, what we are doing is hunting mites in our operation. If you are a hunter or fisherman, you know that the first thing you need to do is to figure out the behavior of the fish. One of the first people to work for me, Mike Andre, he was a trout fisherman who would go fly fishing and he would talk for hours about how he would select his fly. Sometimes they had to be tied green, sometimes brown, depending on what grasshoppers were jumping into the river. He had to know exactly how that fish behaved, what they were eating at that time of year to know how to catch those trout. For us, we need to have a very comprehensive understanding of the mite and mite biology in order for us to treat mite problems.
For this talk, I want to break it up into three sections, first talking about the behavior of the mites. What makes a mite a mite, the behavior of that mite, the vulnerabilities, and how we get rid of it. We’ll also talk about the life cycle of the varroa mite and where it belongs in the tree of life and that might give us some insight on how it behaves and what it does. Then we want to spend some time understanding the population dynamics of varroa mites, especially moving away from just thinking about varroa. Some would argue that mites aren’t the things killing your colonies, but the viruses they transmit that are killing them. We’ll conclude with some treatment options and strategies.
This is the tree of life in the euchareates, more advanced so it doesn’t include some of the bacteria or archaebacteria, which live in thermal vents. If we look at the animal kingdom, we see the protists, which includes nosema as a protist that became the fungi. We can also see the vertebrates breaking off. The mollusks where we can see the crabs and crustaceans. We also see the arthropods. I can’t say enough about them. 80% of life on earth is an arthropod. There are over 100 million ants for every single person on earth. Ants alone weigh more than all the mammals, which includes people, cattle, elephants, and all the wild life. Ants weigh more than all of those collectively. Arthropods are the most successful organisms on earth, and they include bees and mites. If we look at the extent, which means the existing or living arthropods on earth today, you can see it includes the spiders, or the chelicerates. That’s where the mites are included. Recently, they thought the spiders and insects were really closely related but they’ve reanalyzed that now and spiders are very distantly related to the arthropod group. They’re not as closely related. These of course are the centipedes and millipedes, crayfish and crabs, and then the insect. The mites are a part of the chelicerates. This class has a bunch of different organisms: scorpions true spiders, spider scorpions, daddy long legs, and also, the tic. There are over 100,000 of them and these mites are extremely diverse. They’re defined by the fact they have six pairs of appendages — so they have twelve appendages. Four of those are legs, of course. In the blue section is the pedipalp and inside the mouth parts is called the chelicerates, of which they’re named. They have simple eyes, not compound, which means they don’t see very well. They might see some light but they certainly don’t see images. They mostly feed on liquid external digestions, so they’re digesting their food inside of their body and then sucking the nutrients in. If we look at the chelicerate, they are quite admirable. They are tipped with fangs so they’re really good for horror movies, but what they’re doing they’re putting their fangs in and spit into the organism they’ve grabbed, liquify it, and then suck up the juices. That’s how they get their food. Surrounding those chelicerae are pedipalps, which look like stunted legs. The male adapters actually have legs like this because they ejaculate into the pedipalp so they’ve modified that into their mating organ. It actually springs out so sometimes you can see the mated spider because you can see the pedipalp hanging out of her still. For most organisms, these pedipalps have hairs that are used to smell, to sense and walk around the environment.
I’m going to show a video of a deer tick in this process feeding. It tells us a little of how varroa mites might do it. You can see the two pedipalps getting pushed aside there and that chelicerae moving. It’s like a straw when it gets plugged; you have blow out. This tick does the same thing: it starts blowing out enzymes into the flesh of this mammal. Eventually it does that back and forth until it liquefies and the blood becomes easily accessible. It can then suck up that blood. This is a tic, which varroa mites are, and so mites do that same sort of behavior. They’re pedipalps so they are finding the right place and they’re using their chelicerae to cut through that exoskeleton of the bees in order to suck up the liquid. If we look at a close-up of a varroa mite, we can see little pedipalps here and chelicerae surrounding the mouth parts it’s going to use to suck up the juices of the bee.
There are over 50,000 species of mites and ticks. There are at least a million and an amazing diversity of these mites. There are millions and millions per acre of soil mites. There’s some evidence that suggests that tracheal mites started out as soil mites that transferred over onto bees and started living in the tracchia. When people are worried about having the new mite that’s killing all the bees, we’ll get samples and undoubtedly, those are soil mites that bees accidentally brought to the colony.
The hard tick, which the varroa mites are part of, is how they look for their host: they have their legs waiting in the air, waiting for the host to come by and they feed on the host. They have manath floor, which is the mouth part that gets drilled down between the chelicerae. When it’s fully engorged, the female will drop to ground and lay her eggs. In the case of deer ticks, the eggs hatch and they become larva. They’ll get on mammals, birds, or people and fall off again, become nymphs, get onto another host, fall off, get onto deer or other hosts, engorge, and lay eggs. When you see this pattern and see this same mite go to different hosts, that means that this is a great vector of disease because if any of those animals had a disease, then it could suck that disease into the blood and pass it on to the next feeding. When you see this sort of behavior — feeding on more than one host — you expect it be associated with by a vector of some disease in those populations, which is certainly true for varroa. Mites feed on multiple generations of bees and as a result, it’s a great vector of bee diseases, specifically viruses. Of course, in this case, it’s lyme disease. Beekeepers really need to be careful. It was a bad year for deer ticks.
In terms of bees, there are 86 different mites that live with bees. Very few of them are parasites. Most of those are scavenger mites. They live in the bottom board and are eating pollen. Sometimes, you’ll get heavy levels of these feeding mites in your pollen frames. If you’ve ever stored frames of pollen and it gets powdery and misty, it’s probably because you have a heavy pollen mite infestation in there. That also affects native bees, carpenter bees, and mason bees. You can see the pollen shredded up into dust. You have pollen mites and then mites that eat the pollen mites (predatory mites) and then you have hitchhiker mites that basically are using the bees as a bus to move from flower to flower to eat the pollen. We also have parasitic mites that feed directly on the bees and bee brood. One of those of course is the tracchia mite, which came about in the early 80s. This little mite changed our industry. They live in the tracheal trunk of the honey bee and make it difficult to breathe. But, something happened because varroa mite came and the control products for varroa mite also helped control the tracchia mite or that the genetic changes needed by bees in order to keep mites low happened really quickly; a simple genetic switch. We very rarely find tracchia mites at all anymore and they’re not an issue. We don’t find them at high enough levels; we don’t even monitor them anymore.
The mite we are really worried about finding is the tropilaelaps mite. This is a small, oblong Asian mite compared to the varroa. It runs around on the comb very quickly. It’s throughout Asia and on European bee colonies that are kept in Asia, they don’t talk about varroa mite, they only talk about tropilaelaps. They’re going in and having to treat every two weeks to keep this mite in check. Getting this might into the country is one of our biggest concerns.