Enemies of Bees
"Without a doubt, modern apiculture with movable-frame hives and a global trade in bees and bee products is one of the most efficient vectors for disease"--Honey Bee Colony Health: Challenges and Sustainability, Diana Sammataro, Jay A. Yoder, Pg 99
Traditional Enemies of Bees
Traditionally bees have had enemies. Predators, opportunists etc. Some are as large as a Bear and some are as small as a virus.
Ursa. Bears are not a problem for me. Some people live where there are bears and they are their biggest problem. All kinds of bears love to eat bee larvae and they don't mind honey too much either. Symptoms that you have a bear problem: Hives all tipped over and large chunks of the brood nest eaten. Sometimes vandals will tip over hives, but human ones don't usually eat the larvae. The only solutions I've heard of for bears are very strong electric fences with alternating ground wires on the fence (so they are sure to get grounded) and bait on the fence (bacon is popular) so that the bear gets its tender mouth parts on the fence. This seems to work most of the time. Some people put the hives up on a platform too high for the bears, but it is difficult to haul honey down from the platform and move boxes up. Of course sometimes the only way to stop a bear is to kill it and eat it, but the legalities and difficulties of that are best left to a hunting magazine.
Mephitis mephitis and other varieties. Skunks are a common predator of bees all over North America. Symptoms are very angry hives, scratches on the front of the hives, little soggy piles of dead bees on the ground near the hives that have had the juice sucked out of them. Many solutions work fairly well. Putting the hives up higher or having a top entrance, carpet tack strips on the landing board, chicken wire on the landing board, robber screens, trapping, poisoning and shooting. I have really only done the shooting and screen doors, and ended up doing top entrances. But many swear by the other solutions. A raw egg in the shell with the end removed and three crushed aspirin in it with the other end of the egg buried in the ground in front of the hive(s) being harassed is one solution I've heard of that I will probably try next time. Other poisons worry me because of my dog, chickens and horses.
Didelphis marsupialis. Pretty much same problems and solutions as the skunks.
Genus Mus. Many species and varieties. Also shrews (Cry ptotis parva). Mostly these are a problem during winter when the bees are clustered and the mice move in. Using #4 hardware cloth (1/4" squares) over the entrances will let the bees in and out and not the mice. Or use only an upper entrance so the mice can't get in.
Galleria mellonella (greater) and Achroia grisella (lesser) wax moths are really opportunists. They take advantage of a weak hive and live on pollen, honey and burrow through the wax. They leave a trail of webs and feces. Sometimes they are hard to spot because they try to hide from the bees. They burrow down the mid rib (mostly in the brood chamber but sometimes in the supers) and they burrow in the grooves in the frames. Certan is the spores of Bacillus thuringiensis and can be put on the combs to kill the larvae of the wax moth. It is safe for bees and humans. I buy it from www.beeworks.com . Freezing combs will also kill the wax moth. The wax moths will also devastate empty comb that you are storing off of the hive. The only other controls are chemical ones. Some believe that using bacteria in the hive will upset the natural balance in the hive and won't use it.
Caused by a fungus (used to be classified as a protozoan) called Nosema apis. Nosema is present all the times and is really an opportunistic disease. The common chemical solution (which I don't use) was Fumidil which has been recently renamed Fumagilin-B. In my opinion the best prevention is to make sure your hive is healthy and not stressed and feed honey. Research has shown that feeding honey, especially dark honey, for winter feed decreases the incidence of Nosema. Also research done in Russia in the 70's has shown that natural spacing (1 1/4" or 32mm instead of the standard 1 3/8" or 35mm) reduces the incidence of Nosema.
In my opinion moisture in the hive in winter, long confinement, any kind of stress and feeding sugar syrup increases the incidence. By all means, feed sugar syrup if you don't have honey and it means helping a struggling package or nuc or split. By all means, if you don't have honey, feed sugar syrup in the fall rather than let them starve, but, in my opinion if you can, try to leave honey on for their winter stores.
If you are wanting a solution and don't want to use "chemicals" but want to use essential oils and such, thymol in syrup is an effective treatment.
Symptoms are a swollen white gut (if you disassemble a bee) and dysentery. Don't rely simply on dysentery. Sometimes bees get into rotting fruit or other things that give them dysentery but it may not be Nosema. The only accurate diagnosis is to find the Nosema organism under a microscope.
If you want to get a grasp of how necessary (or not) it is to give preventative treatments for Nosema, I will point out a few things that may help clarify this for you. First, realize that many beekeepers have never treated for it, including me. Not only are there many beekeepers who don't want to put antibiotics in their hives, but in fact many beekeepers in the world are prohibited from using Fumidil by law. I am certainly not the only person who thinks it's a bad idea to put Fumidil in your hive. The European Union has banned its use in beekeeping. So we know they aren't using it legally anyway. Their reason? It is suspected of causing birth defects. Fumagillin can block blood vessel formation by binding to an enzyme called methionine aminopeptidase. Targeted gene disruption of methionine aminopeptidase 2 results in an embryonic gastrulation defect and endothelial cell growth arrest. What do they use for treatment in the EU? Thymol syrup.
So why would you want to avoid Fumidil?
Just how dangerous is Fumidil to your hive? It's hard to say exactly, but of all the chemicals people put in hives, it's probably one of the least dangerous. It does break down quickly. It doesn't appear to have a lot of downsides on the surface anyway. But if you're of the Organic kind of philosophy you're still thinking, why do I want to add antibiotics to my hive? I certainly don't want it in my honey and, in my view, anything that goes in the hive can end up in the honey. Bees move things all the time. Every book I've seen on comb honey talks about the bees moving honey from the brood chamber up to the comb honey supers during a cut-down split. Having an area of the hive that is the only part there when chemicals are applied is a nice idea, but it's a lot like a no-peeing section in a swimming pool.
What do antibiotics do to the natural balance of a natural system? Experience with antibiotics would say that they upset the natural flora of any system. They kill off a lot of things that perhaps should be there along with what shouldn't leaving a vacuum to be filled by whatever can flourish. Probiotics have become a big thing in people and horses and other animals now, mostly because we use antibiotics all the time and upset the normal flora of our digestive system. Are there beneficial microorganisms living in bees and beehives? Are they affected by Fumidil? Yes, it's unscientific of me to assume there are without some study to support it, but my experience says all natural systems are very complex all the way down to the microscopic level. I don't want to risk upsetting that balance.
Propping up weak bees.
Yes, those with the Scientific philosophy will find that statement offensive. But I know of no better way to say it. Creating a system of keeping bees that is held together by antibiotics and pesticides that perpetuate bees that cannot live without constant intervention, is, in my organic view of beekeeping, counterproductive. We just continue to breed bees who can't live without us. Perhaps some people get some satisfaction of being needed by their bees. I don't know. But I would prefer to have bees who can and do take care of themselves.
What other non-organic practices may contribute to Nosema?
While the non-organic group tends to want to believe that feeding sugar instead of leaving honey will prevent Nosema, I have seen no evidence of this. Honey may have more solids and may cause more dysentery, but while dysentery is a symptom of Nosema, it is neither the cause nor is it evidence of Nosema. In other words, just because they have dysentery does not mean they have Nosema.
Many of the Honey Bee's enemies, such as Nosema, Chalkbrood, EFB, and Varroa all thrive and reproduce better at the pH of sugar syrup and don't reproduce well at the pH of honey. This, however, seems to be universally ignored in the beekeeping world. The prevailing theory on how Oxalic acid trickling works is that the bee's hemolymph becomes too acidic for the Varroa and they die, while the bees do not. So how is it helpful to feed the bees something that has a pH in the range that most of their enemies, including Nosema, thrive, rather than leave them honey that is in the pH range where most of their enemies fail?
The bottom line is this. You have to make up your mind what your risks are. What you are willing to put in your hives and therefore into your honey. How you want to keep bees. How much you trust a natural system or how much you want to strive for "better living through chemistry"
This is caused by a number of fungi Aspergillus fumigatus and Aspergillus flavus. Extracts from this fungus are used to make Fumigillan used to treat Nosema. Larvae and pupae are susceptible. It causes mummification of the affected brood. Mummies are hard and solid, not sponge-like as with chalkbrood. Infected brood become covered with a powdery green growth of fungal spores. The majority of spores are found near the head of the affected brood. The main cause is too much moisture in the hive. Add some ventilation. Prop open the inner cover or open up the SBB. Treatment is not recommended. It will clear up on its own.
This is caused by a fungus Ascosphaera apis. It arrived in the US in 1968. The main cause is too much moisture in the hive. Add some ventilation. Prop open the inner cover or open up the SBB. If you find white pellets in front of the hive that kind of look like small corn kernels, you probably have chalkbrood. Putting the hive in full sun and adding more ventilation usually clears this up. Honey instead of syrup may contribute to clearing this up, since sugar syrup is much more alkali (higher pH) than honey.
"Lower pH values (equivalent to those found in honey, pollen, and brood food) drastically reduced enlargement and germ-tube production. Ascosphaera apis appears to be a pathogen highly specialized for life in honeybee larvae."--Author. Dept. Biological Sci., Plymouth Polytechnic, Drake Circus, Plymouth PL4 8AA, Devon, UK. Library code: Bb. Language: En. Apicultural Abstracts from IBRA: 4101024
Hygienic queens will also contribute to clearing this up. Hygienic bees will remove larvae before they fungus has created spores.
European Foulbrood (EFB).
Caused by a bacteria. It used to be called Streptococcus pluton but has now been renamed Melissococcus pluton. European Foul Brood is a brood disease. With EFB the larvae turn brown and their trachea is even darker brown. Don't confuse this with larvae being fed dark honey. It's not just the food that is brown. Look for the trachea. When it's worse, the brood will be dead and maybe black and maybe sunk cappings, but usually the brood dies before they are capped. The cappings in the brood nest will be scattered, not solid, because they have been removing the dead larvae. To differentiate this from AFB use a stick and poke a diseased larvae and pull it out. The AFB will "string" two or three inches. This is stress related and removing the stress is best. You could also, as in any brood disease, break the brood cycle by caging the queen or even removing her altogether and let them raise a new one. By the time the new one has hatched, mated and started laying all of the old brood will have emerged or died. If you want to use chemicals, it can be treated with Terramycin. Streptomycin is actually more effective but I don't think it is approved by the FDA and the EPA.
American Foulbrood (AFB).
Caused by a spore forming bacteria. It used to be called Bacillus larvae but has recently been renamed Paenibacillus larvae. With American Foul Brood the larvae usually dies after it is capped, but it looks sick before. The brood pattern will be spotty. Cappings will be sunken and sometimes pierced. Recently dead larvae will string when poked with a matchstick. The smell is rotten and distinctive. Older dead larvae turn to a scale that the bees cannot remove.
Holts milk test:
"The Holst milk test: The Holst milk test was designed to identify enzymes produced by B. larvae when speculating (Host 1946). A scale or toothpick smear is swirled gently into a tube containing 3-4 milliliters of 1 per cent powdered skim milk and incubated at body temperature. If the spores of B. larvae are present, the cloudy suspension will clear in 10-20 minutes. Scales from EFB or sacbrood are negative in this test."
Test kits are available from several of the bee suppliers. Free testing is available at Beltsville Lab:
This is also a stress disease. In some states you are required to burn the hive and bees and all. In some states you are required to shake the bees off into new equipment and burn the old equipment. In some states they will make you remove all the combs and bees, and they will fumigate the equipment in a large tank. Some states just require you to use Terramycin to treat them. Some states if you are treating they will let you continue but if the bee inspector finds it they make you destroy the hives. Many beekeepers treat with Terramycin (sometimes abbreviated TM) for prevention. The problem with this is that it can mask the AFB. The spores of AFB will, for all practical purposes, live forever, so any contaminated equipment will remain so unless fumigated or scorched. Boiling will not kill it. TM will not kill the spores, only the live bacteria. AFB spores are present in ALL beehives. When a hive is under stress is the most likely time for an outbreak. Prevention is best. Try not to let hives get robbed out or run out of stores. Steal stores and bees to shore up weak hives so they don't get stressed. What you are allowed to do if you get AFB varies by state, be sure to obey the laws in your state. Personally, I have never had AFB. I have not treated with TM since 1976. If I had a outbreak I would have to decide what I would do. It may depend on how many hives are affected what I might do, but if I had a small outbreak I would probably shake the bees out into new equipment and burn the old equipment. If I had a large outbreak, I might try breaking the brood cycle and swapping out infected combs. If we as beekeepers keep killing all bees with AFB we will not breed AFB resistant bees. If we as beekeepers keep using Terramycin as a preventative we will continue to spread TM resistant AFB.
"It is well known that improper diet makes one susceptible to disease. Now is it not reasonable to believe that extensive feeding of sugar to bees makes them more susceptible to American Foul Brood and other bee disease? It is known that American Foul Brood is more prevalent in the north than in the south. Why? Is it not because more sugar is fed to bees in the north while here in the south the bees can gather nectar most of the year which makes feeding sugar syrup unnecessary?"--Better Queens, Jay Smith
"The great beekeeper Dr. John Eckert relied solely on having strong colonies for the control of AFB. If he came upon a colony with AFB, he simply combined that colony with the strongest colonies in his apiary and let the bees clean up the disease" --The How-To-Do-It book of Beekeeping, Richard Taylor-->
This is caused by Bacillus para-alvei and possibly combinations of other microorganisms and has symptoms similar to EFB. The easiest solution is a break in brood rearing. Cage the queen or remove her and wait for them to raise one. If you put the old queen in a nuc or the old queens in a queen bank, you can reintroduce them if they fail to raise a queen.
Caused by a virus usually called SBV (SacBrood Virus). Symptoms are the spotty brood patterns as other brood diseases but the larvae are in a sack with their heads raised. As in any brood disease, breaking the brood cycle may help. It usually goes away in late spring. Requeening sometimes helps also.
Breaking the Brood cycle to help with brood diseases.
For all of the brood diseases this is helpful. Even for Varroa as it will skip a generation of Varroa. To do this you simply have to put the hive in a position that there is no longer any brood. Especially no open brood. If you are planning to requeen anyway, just kill the old queen and wait a week and then destroy any queen cells. Don't go three or they will have raised a new queen. Wait another two weeks and then introduce a new queen (order the appropriate amount ahead of time). If you want to raise your own, just remove the old queen (put her in a cage or put her in a nuc somewhere in case they fail to raise a new one) and let them raise a queen. By the time the new queen is laying there will be no more brood. A hairclip catcher works for a cage. The attendant bees can get in and out and the queen cannot.
Small Cell and Brood Diseases.
Small cell beekeepers have reported it helping with brood diseases. Especially once the size is down below 4.9mm. We know that once a cell falls below a certain level the bees chew it out and obviously this is many more cocoons in a large cell than a small cell. (See Grout's research on this). I don't know if it helps with brood diseases or not, but my speculation (and it is merely speculation) on this is that because small cells get chewed out before a lot of cocoons build up where 5.4mm cells get filled with generation after generation of cocoons until they are down around the 4.8mm or smaller size before they get chewed out. This leaves many more places for brood pathogens to accumulate.
Frightened neighbors have been known to spray your hives with raid, but usually they are too afraid to do that and just use pesticides on their flowers to get rid of bees. If they use Sevin many of your bees can die. "Courageous" neighborhood kids have been known to knock over hives in a show of bravery. Gifts of honey to neighbors and perhaps a good PR strategy help. If someone watches you open a hive with no veil it often belays their fears. But you could have the bad luck to open it on a grouchy day and get stung which only reinforces their fears. I'd wear a veil and no gloves and try not to react if you do get stung. That way they see it's not that big of a deal and the bees are not all trying to kill you.
Recently new enemies have turned up.
Varroa destructor (previously called Varroa jacobsoni which is a different variety of the mite that is in Malaysia and Indonesia) are a recent invader of beehives in North America. They arrived in the USA in 1987. They are like ticks. They attach to the bees and suck the hemolymph from the adult bees and then get into cells before they are capped and reproduce there during the capped stage of the larvae development. The adult female enters the cell 1 or 2 days before it is capped. Being attracted by pheromones given off by the larvae just before capping takes place. The female feeds on the larvae for a while and then starts laying an egg about every 30 hours. The first is a male (haploid) and the rest are females (diploid). In an enlarged cell (see cell size section) the female may lay up to 7 eggs and since any immature mites will not survive when the bee emerges, from one to two new female mites will probably survive. These will mate, before the bee emerges and emerge with the host bee. Varroa mites are large enough you can see them. They are like a freckle on a bee. They are purplish brown in color and oval shaped. If you look at one closely or with a magnifying glass you can usually see the short legs on it. To monitor Varroa infestations you need a Screened Bottom Board (SBB) and a white piece of cardboard. If you don't have a SBB then you need a sticky board. You can buy these or make one with a piece of #8 hardware cloth on a piece of sticky paper. The kind you use to line drawers will work. Put the board under it and wait 24 hours and count the mites. It's better to do this over several days and average the numbers, but if you have a few mites (0 to 20) you aren't in too bad of shape if you have a lot (50 or more) in 24 hours you need to do something.
I think that the goal should be no treatments. But these are the common ones.
Several chemical methods are available.
Apistan (Fluvalinate) and Checkmite (Coumaphos) are the most commonly used acaracides to kill the mites. Both build up in the wax and both cause problems for the bees and contaminate the hive. I don't use them.
Softer chemicals used to control the mites are Thymol, Oxalic acid, Formic acid and Acetic acid. The organic acids already naturally occur in the honey and so are not considered contaminates by some. Thymol is that smell in Listerine and although it occurs in Thyme honey, it doesn't occur otherwise in honey. I have used the Oxalic acid and liked it for interim control while regressing to small cell. I used a simple evaporator that Dennis Murrel had on his web site.
Inert chemicals for Varroa mites.
FGMO is a popular one of these. Dr. Pedro Rodriguez has been a proponent and researcher on this. His original system was cotton cords with FGMO, beeswax and honey in an emulsion. The object was to keep the FGMO on the bees for a long period of time so the mites either get groomed or they suffocate on the oil. Later using a propane insect fogger was used to supplement the cords in this control system. The other up side of the FGMO fog was it apparently kills the tracheal mites also. But this could also be interpreted as a down side because you are possibly perpetuating genetics of bees who can't handle Tracheal mites.
Inert dust. The most common inert dust used is powdered sugar. The kind you buy in the grocery store. It is dusted on the bees to dislodge the mites. According to research by Nick Aliano, at the University of Nebraska, this method is more effective if you remove the bees from the hive and dust them and then return them. It is also very temperature sensitive. Too cold and the mites don't fall. Too hot and the bees die.
Some methods are just hive parts or other things. Someone observed that there were less mites on hives with pollen traps and figured maybe the mites fell in the trap. The results were a screened bottom board (usually abbreviated SBB). This is a bottom board on the hive that has a hole covering most of the bottom covered with #7 or #8 hardware cloth. This allows the mites that get groomed off to fall down where they can't get back on the bees. Research shows that this eliminates 30% of the mites. I seriously doubt these numbers but I do like screened bottom boards for monitoring mites and controlling ventilation and helping with any kind of control you actually do.
What I do.
I use the small cell/natural cell and Screened Bottom Boards (SBB) and I monitor the mites with a white board under the SBB. As long as the mites stay under control, and so far, since 2002 they have, that's all I do. If the mites were to start going up while the supers are on I would probably fog with FGMO or dust with powdered sugar. If they were still high after fall harvest, I would use Oxalic Acid vapor. So far I haven't needed them since the bees were regressed. Basically just small cell has been effective for me for both kinds of mites and adequate under normal conditions.
More about Varroa
Without getting into the issue of what methods are best, I think it's significant to the success and sometimes subsequent failure of many of the methods we, as beekeepers are trying to use. I used FGMO fog only for two years and when I killed all of the mites with Oxalic acid at the end of that two years there was a total mite load of an average of about 200 mites per hive. This is a very low mite count. But some people have observed a sudden increase to thousands and thousands of mites in a short time. Part of this is, of course, all the brood emerging with more mites. But I believe the issue is also that the FGMO (and many other systems as well) manage to create a stable population of mites within the hive. In other words the mites emerging is balanced out by the mites dying. This is the object of many methods. SMR queens are queens that reduce the mites' ability to reproduce. But even if you get to a stable reproduction of mites, this does not preclude thousands of hitchhikers coming in. Using powdered sugar, small cell, FGMO or whatever that gives an edge to the bees by dislodging a proportion of the mites, or preventing the reproduction of mites and seems to work under some conditions. I believe these conditions are where there are not a significant number of mites coming into the hive from other sources.
All of these methods seem to fail sometimes when there is a sudden increase in mites in the fall.
Then there are other methods that are more brute force. In other words they kill virtually all the mites. Even these seem to fail sometimes. We have assumed it's because of resistance, and perhaps this is a contributing factor. But what if sometimes it's again because of this huge influx of mites from outside the hive? Granted having the poison in the hive over a period of time when this explosion of population occurs seems to be helpful, it still sometimes fails.
One explanation for this may be that bees robbing and drifting are causing it.
"The percentage of foragers originating from different colonies within the apiary ranged from 32 to 63 percent"--from a paper, published in 1991 by Walter Boylan-Pett and Roger Hoopingarner in Acta Horticulturae 288, 6th Pollination Symposium (see Jan 2010 edition of Bee Culture, 36)
I have not had this happen on small cell... yet. Nor have I had it happen on FGMO. I have seen it happen when I was using Apistan. But others have observed it with FGMO and I have to wonder how much this affects the success of many methods from Sucracide to SMR queens, from FGMO to Small Cell. It seems like there are at least two components to success. The first is to create a stable system so that the mite population is not increasing within the hive. The second is to find a way to monitor and recover from that occasional sudden influx of mites. Conditions that cause the mites to skyrocket seem to be in the fall when the hives rob out other hives crashing from mites and bring home a lot of hitchhikers.
Tracheal mites (Acarapis woodi) are too small to see with the naked eye. This was first called "Isle of Wight disease" as this is where it was first observed and the cause, at the time, was not known. Then "Acarine Disease". Symptoms are crawling bees, bees that won't cluster in the winter and "K" wings where the two wings on each side have separated and make a shape like the letter "K". The mites have been in the US since 1984 that we know of. If you want to check for them you need a microscope. Not a really powerful one, but you still need one as they are too small to see with the naked eye. You're not looking to see the details of a cell, just a creature that is quite small.
Tracheal mites need to get into the trachea to feed and reproduce. The opening to the trachea on an insect is called a spiracle. Bees have several of these and they have a muscular system that allows the bees to totally close them if they want. Since the mites are much larger than the largest spiracle (the first Thoracic spiracle) they have to find young bees whose chitin is still soft so that they can chew out the first Thoracic spiracle enough to gain entry. Once inside, the much more spacious trachea provides the place they live and breed. Tracheal mites must do this while the bees are still 1 to 2 days old before their chitin hardens. A common control for them is a grease patty (sugar and cooking grease mixed to make a patty) because it masks the smell that the tracheal mites use to find a young bee. If they can't find young bees, they can't chew through the spiracle in old bees to get in and so they can't reproduce. Menthol is commonly used to kill the Tracheal mites. FGMO and (by some reports) Oxalic acid will also kill them. Breeding for resistance and small cell are also useful. The theory on the small cell helping is that the spiracles (the openings into the trachea) that the bees breathe through are smaller and the mites can't get in. But since they are already too small it is more likely that the smaller opening is less attractive to the mites who are looking for a hole they can enlarge enough to get in, or the chitin gets thicker the more you get from the edge and they can't chew it wide enough to gain entry. More research is needed on this subject. But basically, I'm just using small cell and they have not been a problem.
Tracheal mite resistance is not hard to breed for and may explain why small cell beekeepers aren't having any problems. If you never treat and you raise your own queens you'll end up with resistant bees. The mechanism of resistance to tracheal mites is not known. One theory is that they are more hygienic and groom off the tracheal mites before they can get in. Another is that they have either smaller spiracles or tougher spiracles that the mites can't get access through. Another could be similar to the grease patty treatment, in that the younger bees may not give off the odor that triggers the tracheal mites to seek them.
Acarapis dorsalis and Acarapis externus are mites that lives on honey bees that are indistinguishable from Tracheal mites (Acarapis woodi). They are classified differently simply based on the location where they are found. Leading to the obvious question, are they the same and they are just not able to get into the trachea.
Small Hive Beetles.
Another recent pest that were first identified in the US in 1996 and in Nebraska in 2007, is the Small Hive Beetle (Aethina tumida Murray). Sometimes abbreviated SHB. The damage they do is similar to the wax moths but more extensive and they are harder to control. If you smell fermentation in the hive and find masses of crawling, spiky looking larvae in combs you may have SHB. The only chemical controls approved for use are traps made with CheckMite and ground drenches to kill the pupae, which pupate in the ground outside the hive.
While I have seen a few, I have not had any issues with these, but I will probably go to more PermaComb in the brood nests if they ever become too much of a problem. Strong hives seem to be the best protection. Putting hives in full sun seems to help. The eggs don't hatch if the temperature falls below 86o F (30o C) or the humidity falls below 34% so you can leverage that to protect pulled supers or unguarded combs by putting them where they are dry and cool. I have more faith in the "dry" than the "cool". The larvae, once they do hatch, are very tough and can chew through plastic.
Copyright 2006 by Michael Bush