The Purdue Plant and Pest Diagnostic Laboratory

What's Hot on March 19, 2007
at the P&PDL!

What’s happening to our bees?!?!

Greg Hunt, Associate Professor, Department of Entomology, Purdue University

Listening to the news, it seems like it’s getting hard to keep bees alive these days.  Last year it happened again, but now there’s a new name for it: colony collapse disorder (CCD).  Every three to five years it seems we have large die-offs of bee hives across fairly large regions, at least since the parasitic tracheal mites and Varroa mites entered the U.S., which happened in the mid 1980's.  Tracheal mites are not as bad now that most of our bees have pretty good resistance, but Varroa mites are still the major problem.  Varroa transmit viruses and make the brood diseases worse, leading to colony population collapses that beekeepers call parasitic mite syndrome, or PMS, which usually is manifested as diseased brood in the hive, adults with virus, and inability to rear healthy brood.  This past year beekeepers and researchers reported something they first called “fall dwindling” but are now calling “CCD”.  This syndrome does seem unusual.  CCD is different from typical PMS because the bees fly out and fail to return to the hives, leaving only a few young bees and apparently healthy brood.  This might mean that whatever is hitting the bees is killing them quickly and that different pathogens or stresses are involved than what we usually see.  But symptoms like this have been observed before, even before the mites arrived. They used to talk about the “disappearing disease”, which meant the colony just dwindles, with very few or no dead bees lying around the hive.  No one has ever figured out the cause.  Jim Tew has an excellent article about this on the web:

Among the things that could cause bees not to return to the hive are Nosema disease which causes dysentery, or tracheal mites, or viruses.  In fact, when your bees get typical parasitic mite syndrome and show diseased brood, the colony often dwindles without many dead bees in the hive, although you often see bees crawling around with deformed wings (probably caused by deformed-wing virus).  Where did all the other bees go?   Last year, it seems there was rapid dwindling of bee hives in fairly large areas.  The press release originating from Penn State has gotten a lot of play.  The preliminary analyses of samples showed a significant amount of Varroa in hives that had dwindled, suggesting that maybe mites were a factor.  They also saw various confusing symptoms in the dead bees.  There is definitely something going on, but it may not be something new. Nosema, or dysentery disease is caused by Nosema apis (a spore-forming protozoan).  In Europe they recently found Nosema cerana associated with dying hives. Like Varroa mites, N. ceranae came from the Asian honey bee, Apis cerana.  It is controversial whether N. cerana is the cause of those colony deaths in Europe.  I recently talked to a virologist (Judy Chen) at the USDA bee lab in Beltsville and she had checked for N. cerana in the U.S. and said that it was common.  Tom Webster at KSU also found N. ceranae in samples said to have CCD.  We don’t know how long this pathogen has been in the U.S. because nobody tested for it before! Maybe N. ceranae is a factor in CCD.  Nobody knows.  Nosema is considered a minor pathogen of bees but, fall application of Fumagillin (Fumadil-B) in sugar syrup will protect your bees from both kinds of Nosema that could weaken your hives.

In 2006, CCD was primarily a problem of migratory beekeepers.  Moving bees causes them to be stressed, especially when they do not have good food sources.  Devon Howald from Huntington, along with Dave Shenefield of LaFountaine took about 1500 hives from IN to CA and some of them dwindled while waiting for the almonds to bloom.  But the ones that had access to good nectar were OK. They hope to at least break even after spending a lot of money in freight costs.  Four out of five migratory beekeepers they spoke to in CA were seeing dwindling hives. The press release that generated this “buzz” included data from a survey by Bee Alert Technologies which showed CCD was a problem in 25 states on a map.  However, some of the states on that map did not report widespread symptoms of CCD.  They originally said IN was affected, but have updated the map.  See, for Zachary Huang’s CCD page.

The problem we had in Indiana this winter was no fall nectar flow and those who did not have time to feed their bees lots of sugar syrup early enough in the fall had colonies that starved.  And it seems that the colonies had virtually no pollen in the combs which is an important source of protein for the bees during the winter.  Clover Blossum Honey Company in LaFountaine may have 50% losses in many areas due to starvation.  They can split their hives and make this up, but that is a lot of work.  I am guilty of allowing starvation to take half of our Purdue hives. Leaving your supers on until September helps when there is a poor fall flow because it allows your bees to draw some of the honey from the supers down into the brood nest, but if there is no nectar flow in the fall they may still need syrup.  My opinion is that there is no reason for beekeepers to worry about mysterious ailments.  Hopefully, researchers will be able to provide answers.  We beekeepers should monitor our hives for Varroa mites and control them when they get too high, preferably with “soft” chemicals, and we need to try to find bees that can tolerate the mites (E201, Parasitic Mites of Honey Bees).  In the fall and early spring, we should check our bees and feed if necessary.  If we do these things, our bees will be OK.  If you move your bees around for pollination, you will have to be careful with their nutrition and you may have to take losses sometimes.  Hobby beekeepers are responsible for a large proportion of the pollination services of honey bees and an important part of agriculture.

Click image to enlarge

Varroa mite on honey bee

European honey bee with a Varroa mite on its back. The mites cause death and disease in bee colonies.

Photo courtesy of Scott Bauer, USDA-ARS



Photo courtesy of Greg Hunt

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service