Winter loss survey NOW OPEN and Dead colony Necropsy

The PNW honey bee survey is now open extending to end of April. WVBA has had consistently great participation in past surveys (38 survey returns last year – loss level 46%) and I AKS PLEASE complete a survey again this year. Go to To examine past survey results look for WVBA survey report on same site under survey results.

NOTE: I prepared the information below on necropsy for posting in March – somehow it did not get on the site. So I will repost this month.

We lose bee colonies for a variety of reasons over the winter season and sometimes  during the active season.   A Best Management Practice is to do a hive necropsy – examine the dead colony to determine a probable cause for colony demise. Anna Ashby talked on dead colony necropsy to a new bee group forming in Sherwood. I published article on Dead colony autopsy in Bee Culture June 2018.

Reasons for death of an entire colony are varied. Loss may be due to environmental extremes, specific bee pathogens or pest activity, pesticide exposure (external as well beekeeper internally applied pesticides) or internal colony social dysfunctions, especially related to queen replacement. By and large, most colony loss can be attributed to the beekeeper doing something incorrectly or, more frequently, missing the signs/symptoms, and/or not properly intervening in a timely fashion, especially related to varroa mites.

Dead bee hive necropsy is an imprecise science. Determination of the reason/reasons for colony failure may not always be possible.  Examination of a dead colony might help eliminate some possible causes, leading to a probable diagnosis or at least a shorter list of possible reasons for loss.

The most likely reasons for overwinter loss are starvation or too small an early spring colony population (which might have one or more root causes); loss of  colonies in the fall almost always is due to varroa mites. Seasonal losses are often related to unsuccessful queen replacement. Disease/pesticides/pests/environment can be contributing factors or primary loss reason any time. Management, or lack of, can be an important loss contributor.

Performing a hive necropsy

Diagnosis begins with consideration of seasonal life cycle. Start outside immediately in front of dead colony to determine if dead bee numbers are normal or excessive and if there is something abnormal (colony not upright, etc).  Heavy amounts of bees/debris within the hive or on the bottom board should be examined. Sometimes weather data should be consulted.

In most instances close examination of boxes and  frames will be needed. Look for disease symptoms, neglect of brood, brood pattern, brood remains, extent or evidence of mites, presence of honey and bee bread stores, fecal remains, presence/absence of scavengers (wax moth/small hive beetles/maggots), evidence of previous queen rearing and other unordinary features. Note: See Caron 2018 Dead colony forensics  for details on how to look for and assess signs/symptoms of a dead colony. Also see article by Meghan Milbrath “Why did my Honey Bees Die?”

The longer the delay in looking at a dead colony, the greater the possibility that mold, robbing of stores, scavenger activity, etc. may interfere with an examination.  In a diagnosis initially consider the odds and consider the most likely reason for loss relative to the season. If loss occurs during the fall (before bees hunker down into their cluster) seek to determine if loss might be due to something different than varroa mite (and their transmission of viruses). In spring colony death, seek to determine if loss could be other than too small a population or starvation (bees ran out of food stores).

Varroa mites are all too frequently the reason for colonies with low adult populations. A colony judged too small in the spring might in fact have a reduced population because of mites. Likewise a spring starvation might ultimately be due to heavy mite numbers during the fall when the colony raised too few of the fat body heavy diutinus bees or did not have adequate numbers of adult field bees to store adequate stores. Proper, timely mite control can help avoid weaker colonies so when doing a necropsy on what appears to have been a weak colony determine what /when mite controls were performed.