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Phil Craft

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Dear Phil, I have been trying to sort out my thinking about – AFB and come down to the essay below.  Please read it critically and let me know of any loopholes in my information and logic. I am not going anywhere with this essay but I would suggest that if you run out of questions, you might do a piece on modern handling of the AFB situation and what you and others may see about its management in the future.

Some diseases, American Foulbrood of Honey bees (AFB), for example, don’t lend themselves to eradication. A large feral population of bees in which AFB can exist with impunity lies outside of the range of normal beekeeping activities. Yet States have passed laws for the control of AFB.

In the 1930s, when I was a teenager, the bee inspector from the New York State department of agriculture detected AFB in one of my three colonies. By law I had to kill all the bees, burn the hive and bury its ashes. Today some 80 years later the law still stands, requiring the same treatment.

Although today, an antibiotic, Terramycin, controls the vegetative stage of AFB bacteria, it does not kill its spores, which still hide in the combs and equipment allowing flare-ups of the disease. The entire beekeeping industry in this country now depends on that one antibiotic, which, when it fails, sends the beekeeper back to burning his bees and equipment. Eventually Terramycin will fail completely.
Whatever, The beekeeping industry is in dire need of better control measures for AFB than the incomplete control that Terramycin affords with its back-up of kill the bees with their brood, combs, and frames when Terramycin fails.

Phil replies:
Fortunately American Foulbrood is not a widespread problem, but when it strikes it is extremely serious, almost always ending in the death of the colony and the rapid spread of AFB to nearby hives and wild colonies. I agree that eradication of this highly contagious disease is unlikely, in part because of the continued presence of feral, or unmanaged, colonies in trees and manmade structures.

AFB is a bacterial disease of honey bee larvae. Though adult bees spread it, they are not susceptible to it. Like nosema, AFB is a caused by a spore forming organism. (See my March ’15 column for a Q&A about nosema). Whereas nosema spores are created in infected cells in the guts of adult bees, those of AFB are produced in the guts of larvae and pupae. The dead pupae decompose into a dark, gooey mass which dries over time and forms a dark, hard crust. This crust, referred to as scale, adheres firmly to the lower sides and bottoms of the cells. A single AFB scale can contain as many as 2.5 billion spores, and a single spore can be sufficient to infect a larva. In some ways spores are like seeds, but another way to think of them is as a sleeping form of the disease. They can remain viable for decades in food, wax, or woodenware, resistant to high temperatures, disinfectant chemicals, and ultraviolet light. The bacteria enter the food supply when honey bees pick up spores on their mouths as they clean infected cells or when nectar and pollen are stored in infected cells. When spores are fed to a very young larva via contaminated food, the bacteria enter what is known as the rod, or vegetative stage, during which they are not infectious. In that state, however, they grow rapidly inside the larva, each bacterium capable of producing millions of new spores before it dies. And so the cycle continues.

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AFB not only spreads quickly within an infected hive, but also from hive to hive and apiary to apiary. Colonies which have succumbed to or have been weakened by AFB are susceptible to robbing by bees from stronger, uninfected hives. The robbers carry spores back to their own colonies in contaminated honey. That’s why you’re correct in saying that, even if we could eliminate AFB in managed colonies, feral bees would be a continual source of re-infection. Another source is the beekeeper him or herself. The disease is easily spread in the course of moving frames of comb from one hive to another for swarm control, the creation of nucs, or to reinforce a weak hive, etc. It can also be introduced in purchased hives or nucs and in used equipment – especially used comb.

The best way to avoid unintentionally spreading AFB through the movement of hives or frames is to learn to recognize the signs of the disease. It is often characterized by scattered capped brood cells interspersed with empty cells where pupae have died and been removed by the bees (though other conditions can also result in scattered brood.) The cappings that remain are dark, sunken, and sometimes greasy in appearance (dark capping may have other causes as well), and often contain punctures – a result of bees opening the cappings to remove infected or dead brood. Of course, foulbrood gets its descriptive name from the pungent or foul odor that infected brood emits. However this AFB bouquet may not be detectable in early stages of the disease, and for beekeepers with limited experience, the smell of decaying brood, dead from other causes such as Varroa mites, may lead to misdiagnosis. Almost every Fall, I receive calls from panicked novice beekeepers, concerned that they are smelling AFB in their hives, when what they are sniffing is instead the pungent odor of fresh aster nectar. The only definitive way to diagnose AFB, other than sending samples to a lab for testing, is the ropiness test in which a toothpick or twig, inserted into a suspect cell and then slowly pulled back, draws out a strand of liquefied pupa with a sticky, ropey appearance. The absence of this phenomenon doesn’t indicate the absence of foulbrood since the pupa may not yet have decomposed to that extent or may already have become desiccated, but its presence is confirmation of AFB.

Because it is so highly contagious and has been around so long, American foulbrood is the reason that state apiary programs were originally created. Although the role of state apiarists has expanded and adapted to cope with modern beekeeping challenges, many states still have regulations, like the NY law you cite, requiring mandatory inspections and compulsory burning of infected hives. In practice, most state apiary programs are not staffed to conduct mandatory inspections of small scale beekeepers, and only perform inspections to them upon request, and on a schedule permitting basis. However, when any beekeeper suspects AFB and asks for assistance in diagnosing or managing it, a quick response by apiary inspectors is the norm. Not only can the appearance of AFB in a single hive result in the loss of an entire apiary of bees and valuable equipment, but the chances are also high that neighboring apiaries and feral colonies will become infected as well. State apiarists take this risk very seriously.

For many years, the only recourse for an outbreak of AFB was killing the bees and burning the hives – body, frames, and all. Eventually, sulfa drugs offered an alternative to destruction, and then the antibiotic Terramycin (oxytetracycline) came along and seemed like a panacea. Beekeepers embraced it and used it liberally, some at the first sign of foulbrood, others routinely to prevent outbreaks. Many experts encouraged this practice. Predictably, frequent use has led to significant Terramycin resistance in some areas. In 2005, the FDA approved another antibiotic, Tylan (tylosin), for the treatment of Terramycin resistant AFB in honey bees, and since then a couple of generic versions of tylosin. However, as you point out, the problem with any antibiotic is that it only kills the bacteria in the active, vegetative phase inside the larval host. It does not kill the numerous, long lived spores which continue to be a source of infection to other colonies. Antibiotics mask AFB by suppressing the stage of the disease which produces symptoms, but they do not eliminate it. I think that the best response to an outbreak of AFB is still to burn infected hives and to monitor others for signs of the disease.

That does not mean, however, that we’re back to early 20th century methods of dealing with AFB. Though we may not be able to eliminate it, we have a new tool for limiting the spread of foulbrood in the form of bees selected and bred for hygienic behavior. Hygienic behavior is an interesting and valuable behavior naturally expressed by honey bees to control brood disease and parasites. It consists of detecting, and removing from the hive, brood damaged by disease or parasites. A clearly visible example with which some beekeepers may be familiar is the removal of pupae infected by chalkbrood, another brood disease of honey bees caused by a fungus. Outbreaks, usually occurring in the spring, are normally short in duration and not considered serious though, if persistent, they can be harmful. The infected larvae die shortly before or after being sealed in the cell, and dry into white mummified remains which resemble small pieces of chalk – hence the name. Typically, beekeepers first become aware of the disease when they see numbers of small, white bodies littering the entrance and the ground in front of the hive. Hygienic behavior is also recognized as a tool in the control of varroa mites, especially when enhanced through selective breeding.

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The value of this trait for the control of American foulbrood was first described by researchers in the 1930s, and considerable additional research was conducted in the 1960s and 70s. More recently, Dr. Marla Spivak and her students at the Univ of MN have developed a line of highly hygienic honey bees, called Minnesota Hygienics. The USDA Baton Rouge Honey Bee Lab has produced two others: the SMR line (short for Suppression of Mite Reproduction), and the Russian Honey Bee line. Hygienic bees suppress outbreaks of AFB and inhibit its spread by removing infected larvae from the hive while the bacteria are still in the vegetative stage before they produce new spores. Requeening hives with hygienic queens can improve a colony’s resistance to several diseases and pests, and is especially beneficial in hives which display no foulbrood symptoms but share an apiary with a hive which has been affected by AFB.

In summary, though we cannot eliminate AFB, we can control its spread and prevent the devastating losses that accompany large outbreaks by the following means:

Prevention: Reduce transfer of diseases, including AFB, by moving only healthy hives, brood, bees, and equipment into our apiaries. This requires careful inspection when purchasing bees or used equipment, and novice beekeepers will likely require the advice and assistance of those with more experience. Within an apiary, bees and comb should never be transferred from any diseased or weak hives into healthy ones.
Diagnosis: Open hives regularly to monitor their health. Learn to recognize the signs of AFB and be especially attentive to colonies which are failing to thrive. Any diseases or parasite issues should be dealt with promptly. Newer beekeepers can use the resources of their local beekeeping group, apiary inspector, or USDA labs in making diagnoses.

Control: Catching an infestation early and burning the infected hive or hives is the only way to eliminate it. Antibiotic medications registered for the control of AFB only mask symptoms of an outbreak, do not stop its spread, and suppress its signs only as long as they are used continually. They should not be used prophylactically. In order to minimize the spread of the infection to neighboring apiaries, consultation with state apiary officials is highly advisable. In some states it’s required. It is important to do follow up inspections of surviving hives and to act promptly if further signs appear. Re-queen surviving hives with hygienic queens.

Thanks for a good question, and your thoughts.

A beekeeper in Ohio writes:
Phil, … [do] you know of anything that can be used on apple and cherry trees that is not toxic to bees.  I have 17 hives here north of Dayton, OH and also have fruit trees.  Most of what I’ve found is very toxic to bees.

Phil replies:
Though I am not a fruit grower, I have spent time with beekeepers who are, and have also heard horticultural extension specialists discussing the treatment of fruit trees for insect pests. It has made me very aware of the difficulty of killing insect pests in the orchard while not harming desirable insects. For answers to your question, I sought out some real experts on the topic at the University of KY: Dr. John Strang, Fruit and Vegetable Extension Specialist, and Dr. Ric Bessin, Entomology Extension Specialist, both of whom have experience as beekeepers.

For backyard apple growers, they recommended the use of oil and Bt (Bacilllus thuringiensis) as non-conventional chemical insect controls. Dormant or summer oils, mixed with water, are used to control insect pests by interfering with their breathing. They can be used in ways and seasons which make them safe for honey bees and other beneficial insects. I discussed Bt in a Q&A concerning wax moth control in the July 2014 issue of Bee Culture. It is a bacterium which is classified as a non-chemical, bio pesticide. There are a number of subspecies of Bt, each effective at killing a different, specific insect species. By targeting specific insect pests, Bt causes no collateral damage to pollinators such as honey bees.
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Other chemical options to protect apples from insect damage include the use of the pesticides Surround, and Entrust. The main ingredient in Surround is a type of clay called kaolin, which creates a non-toxic film barrier between the pest and its host plant. Kaolin is an edible mineral long used as an anti-caking agent in processed foods and in such products as toothpaste. Spinosad, the active ingredient in Entrust, is produced by fermentation of the fungus-like bacterium Saccharopolyspora spinosa, which was originally discovered in Caribbean soil. Spinosad is also available in many other pesticides. Entrust/spinosad is toxic to honey bees and other pollinators during the spraying process and while the spray material is still wet. Once spray residues have been allowed to dry for three hours or less the residue has low risk for honey bees. Both Surround and Entrust, as well as their ingredients, are considered organic approved. However, organic certification for growers is conducted at the state level, and regulations will vary state to state. If you are certified organic, or seeking organic certification, you need to consult the certification agency in your state.

A non-chemical alternative is to enclose apples in three-pound special paper bags once the fruit reach ¾ of an inch in diameter. Bagging can be very effective at excluding diseases and insects and avoiding the use of pesticide sprays in orchards with only a few trees. For more information on bagging apples, see: http://www2.ca.uky.edu/entomology/entfacts/ef218.asp.

Backyard cherry growers have fewer bee-safe insecticides available. Only the use of oil, Bt, and the pesticide Entrust, are recommended.

If you decide to use a chemical spray, controlling flowering weeds in the orchard will help to keep honey bees away during critical times for insecticide application. It is also very important not to spray insecticides during bloom. In commercial situations, where honey bees are brought in for pollination, hives need to be removed promptly at the conclusion of the bloom. 

Since I live in KY, I sought the advice of extension specialists at the Univ of KY, however, all states have similar agricultural specialists. If you are growing fruit, you should get to know the specialists in your state. Your local county extension agents also work with both local growers and with beekeepers, and help with answers to your questions. Using my suggestions as a starting point, you should conduct your own research and consult local experts in OH.