Other things can cause an occasional case of deformed wings [...]]]> Deformed wing virus (DWV) is one of the viral diseases associated with Varroa mite infestations. Although the disease is also found in colonies not infected with Varroa, it appears to be both more common and more destructive in colonies where mites are well established.

Other things can cause an occasional case of deformed wings and a diagnosis is impossible without laboratory tests. However, if you see a young bee with distorted, misshapen, twisted, or wrinkled wings, there is a good chance you are seeing the results of deformed wing virus.

In untreated hives, the Varroa mite population skyrockets in late summer and early fall. The mites had all spring and early summer to build up and now, when the drones are being evicted and the honey bee population is shrinking, the number of mites may overwhelm the number of bees. When the viruses also become concentrated in the remaining bees, symptoms are more likely to be apparent to beekeepers.

Bees with deformed wings do not live very long. The one shown below wandered out of the hive this morning and was fluttering her misshapen wings and running in a circle when I found her.

Rusty

A honey bee with severely deformed wings

Spring colonies that have overwintered face a particularly daunting set of circumstances. For example:

Whoa! There are at least two things wrong [...]]]> Yesterday I read the following statement on the blog of a well-known beekeeper. “First I looked at the hive entrances which had signs of nosema the last time I visited. The hive looked just the same – no new nosema on the side of the hive.”

Whoa! There are at least two things wrong with this statement. First off, you cannot see Nosema on the side of a hive. What you can see on the side of a hive is bee feces, which may or may not contain Nosema. More often than not, an accumulation of runny brown feces at the entrance to a hive in spring is honey bee dysentery. Unlike human dysentery, honey bee dysentery is not caused by a pathogen but by poor diet.

It is true that Nosema apis also causes diarrhea-like feces to be deposited in or on the hive, but it cannot be distinguished from dysentery without a laboratory analysis—or at least a microscope and some training.

Secondly, Nosema ceranae, which also can infect honey bees, does not cause the bees to defecate in or on the hive. Most often bees become infected with Nosema ceranae in the summer and die in the field while out foraging. In any case, bees infected with Nosema ceranae do not leave diarrhea-like feces as a clue.

In summary, seeing no feces does not mean the bees are free of Nosema anymore than seeing feces means they are.

Rusty

The [...]]]> While studying pesticides in pollen, I was always curious about the potential for pollen to carry disease organisms as well. Indeed, a new study that appeared in the December 22 PLoS ONE confirmed my worst fears—that pollen may be a major route of viral infection from managed honey bees to wild native bees.

The authors of the study examined the four viruses that are most commonly found in North American honey bees—deformed-wing virus, sacbrood virus, black queen cell virus, and Kashmir bee virus—plus Israeli acute paralysis virus, which is often found in conjunction with colony collapse disorder. They asked a number of questions about bee-to-bee disease transmission and then set up a series of experiments to answer those questions.

They found eleven species of wild pollinators in Pennsylvania, New York, and Illinois that carried at least some of the viruses. These viruses were much more likely to show up in wild pollinators that lived near apiaries known to be infected with the various pathogens.

Tests on both the pollen and the bees themselves showed that in many cases disease-free foragers were carrying pollen loads that contained viral diseases—especially deformed-wing virus and sacbrood virus. This finding indicates that the pollen, itself, may be capable of transmitting the disease from one bee to another—it may not be necessary for an infected bee to pass the virus directly to another bee. Similar to human viruses that survive on door knobs, these bee viruses appear to survive on pollen grains.

In other experiments, honey bees and bumble bees kept in greenhouses were shown to transmit Israeli acute paralysis virus among themselves by simply foraging on the same flowers. The disease moved freely in both directions, from honey bees to bumble bees and from bumble bees to honey bees.

The authors point out that the exact mechanisms of disease transmission via flowers and pollen are not understood and more study is needed to see if host plants have a greater role in disease transmission than just as physical carriers. In the meantime, it is important for beekeepers to understand the impact diseased honey bees may have on wild pollinator populations. Honey bee health needs to be a priority if we are to maintain the health—or perhaps the very existence—of wild pollinator populations.

For more information, you can download the complete paper for free at http://www.plosone.org/article/info:doi/10.1371/journal.pone.0014357.

Rusty

A simple leg count is probably the easiest way to tell an arachnid from an insect. Insects—including bees—have six [...]]]> So what is a mite anyway? Generally, a mite is an invertebrate animal in the class Arachnida—a name that comes from the Greek word for spider. Like most other arachnids, mites have eight jointed legs.

A simple leg count is probably the easiest way to tell an arachnid from an insect. Insects—including bees—have six legs. In addition, arachnids have no wings or antennae. However, since both arachnids and insects belong to the phylum Arthropoda, they have many structures in common—one of these being a protective exoskeleton.

As a general rule, mites tend to be smaller than insects; some are even microscopic. Many types of mites—at least fifty or more—can be found inside a beehive, and most of these were carried there by the bees themselves. For the most part these are harmless, non-parasitic mites that were feeding on flowers, pollen, nectar, detritus, or other mites when they were picked up inadvertently and flown to the hive. These will usually die and become part of the frass that routinely collects on the bottom board.

Since mites have no wings, they often attach to insects and hitch a ride to a new location. Mites that move this way are called phoretic. Whether the mites in a colony of bees arrive by design or by accident, an overwhelming majority do no harm and may even be beneficial for consuming detritus.

However, some mites are parasitic, and two of these are famous for wreaking havoc on honey bee colonies. The first of these, Acarapis woodi, is known as the tracheal mite. As the name implies, this microscopic creature lives and reproduces inside the tracheae (or breathing tubes) of the honey bee. They bite into the wall of the trachea and suck the hemolymph or “bee blood.” This not only weakens the bee, but the wound allows the entry of secondary infections.

The most famous parasitic mite, Varroa destructor, is found on the external surface of both pupal and adult bees where it also feeds on the hemolymph. It is closely related to several other species of mite that have long been known to affect Apis cerana, the Asian honey bee. By mite standards, Varroa destructor is very large, and it is huge compared to the size of the host honey bee. Besides weakening the bees by consuming their body fluids, it is thought that Varroa mites carry a number of bee viruses that transfer to the bee through its bite.

Mites are spread easily and quickly from hive to hive. Beekeepers spread them during routine hive management and migratory beekeepers spread them from one apiary to another and one region to another. Bees also spread them when drifting, swarming, or robbing. Mites can even be spread when the bees are foraging. Several other species—including bumble bees, scarab beetles, and flower flies–have been found to carry Varroa mites from place to place. Although Varroa are harmless to these species due to their vastly different life cycles, the mites are glad to hitch a ride whenever the opportunity presents.

Rusty

I’ve deliberately avoided writing about it—partially because [...]]]> Hardly a day goes by when someone doesn’t mention colony collapse disorder to me, either in person, in an e-mail or comment, or on the phone. “I hear they found the cause of CCD!” is a statement I’ve heard dozens of times over the last few years.

I’ve deliberately avoided writing about it—partially because I didn’t know much about it myself and partially because there was (and continues to be) a great deal written by people who know very little. It’s hard to compete with the press.

But, at this point, I believe competent research by a legion of intelligent scientists has given us some answers. Consequently I am now going out on a limb to give you my personal interpretation of that science. Although it is a complex subject, I will try to make it as simple as possible. So here goes.

Virtually all living things carry viruses, including plants, animals, and bacteria. The organism in which the virus lives is called the host.

The CCD Connection: Honey bees are hosts to least 18 known viruses. Most of these viruses have been recognized for a long time.

Viruses survive by taking over the genetic machinery of the host. Simply put, they instruct the host to stop doing whatever it is doing and replicate the virus instead. While viruses cannot walk, swim, or fly they are easily transmitted by contact between individuals or by a vector. A vector is simply a carrier that transmits an infectious agent.

The CCD Connection: The introduction of Varroa mites gave bee viruses the boost they needed to spread rapidly and widely throughout the honey bee population. Varroa mites carry many bee viruses in their bodies and transmit them with their bite.

However, viruses are usually inactive. They live in the host organism but don’t do harm because they are suppressed by the immune system of the host. The amount of a virus that lives in an organism but does no harm is known as the background level. [Think of a human “cold” virus. Although cold viruses are everywhere, we usually show no symptoms of a cold because our immune systems suppress the virus.]

The CCD Connection: Many bee viruses can be found in healthy colonies of bees. As long as the colony remains healthy, the viruses remain in the background and cause no problem.

Sometimes the immune system becomes ineffective at suppressing the viruses. Immune systems become less effective when an organism is stressed. Apparently, the energy of the host goes into compensating for the stress rather than maintaining the immune system. [So although cold temperatures by themselves don’t cause colds in humans, becoming chilled may suppress the immune system long enough for the virus to take over.]

The CCD Connection: Honey bee colonies are becoming more and more stressed. Many of the stressors are similar to human stressors, for example poor nutrition, exhaustion, chilling, and disease. In addition, honey bees are exposed to environmental toxins such as pesticides, and the excessive fear, noise, and incarceration imposed by migratory beekeeping. Worst of all,Varroa mites not only distribute viruses but weaken the bees by sucking their hemolymph (insect blood.)

When groups of organisms live together, just a few individuals with compromised immune systems may manufacture enough excess virus to infect other individuals. Instead of the usual background levels of virus, there are now overwhelmingly large numbers of virus.

The CCD Connection: Disease spreads quickly whenever individuals live close together–and honey bees are no exception. Honey bees live close together within the colony, but they also live close to other colonies within an apiary, close to hundreds of other colonies on the back of a truck, or thousands of other colonies in a vast orchard.

The presence of many sick individuals (another stressor) combined with an overwhelming number of virus organisms suppresses the immune function of the remaining hosts and, before you know it, the entire group is susceptible to any number of other infections. Other viral diseases that had been living in the background start to replicate and other organisms, such as bacteria, fungi, or microsporidia set up housekeeping in the compromised body of the host.

The CCD Connection: Collapsing colonies are usually found with multiple viral infections or viral infections in tamdem with some other pathogen, such as the microsporidian Nosema ceranae. And nearly all collapsed colonies have been found to be infested with Varroa mites. This evidence works well with the model described above.

In summary, I believe that the ultimate answer to the CCD question will be some combination of multiple disease organisms and multiple stressors. Unquestionably there is more to know. There may be some viral pathogen that is worse than others, or some combination of pathogen/parasite/stressor that sets off a domino effect. But are we going to find one stressor, one organism, or one management error we can fix overnight? I think not.

As I’ve said before, CCD has served honey bees well in that it has focused attention on apicultural and agricultural practices that are simply unsustainable. Even if we ultimately “fix” CCD, unless we clean up our act another catastrophe is sure to follow.

Rusty