Identifying Signs of Honey Bee Disease

To inspect a colony for disease, examine several brood frames to look for irregular laying patterns, discolored larvae, perforated wax cappings, or any other irregularities that could signal disease.
Deformed wing virus (DWV)

Infected bees have wings that appear malformed, crinkled, shrunken, twisted or entirely missing.
European foulbrood (EFB)
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Infected larvae may appear yellow, brown or gray. Healthy larvae are always curled in a “c” shape, but EFB infected larvae may look twisted, stretched out or even facing up inside the cell. Infected larvae may also become translucent and causing the trachea (a white line) to be visible. In later stages the larvae appear melted. The hive may have a spotty brood pattern and a sour smell. Conduct the rope test to determine if it is EFB or AFB. ​
American foulbrood (AFB)

​Unlike EFB, AFB primarily affects sealed or capped brood. Look for a spotty brood pattern and brood capping that appears sunken and moist. Also look for perforations or pinholes in the capping. Sometimes a pupa infected with AFB will melt into goo, however its tongue will remain attached to the top wall of the cell. Once it dries out completely it will turn into a hard black scale at the bottom of the cell. Colonies infected with AFB smell foul. Conduct the rope test to determine if it is EFB or AFB.

​AFB is highly contagious and is a reportable disease, so if you suspect an AFB infection contact your local state Apiary Inspector or extension office immediately.

Learn more about AFB from Cornell’s Dyce Lab YouTube video, “American Foulbrood.” *Practicing looking for signs of the disease starts at the 7:30 minute mark. ​
How to conduct the rope test

​Identify a dark sunken capped cell or melted down larvae. Insert a toothpick in it and stir gently. Pull the toothpick out slowly. If the goo stretches out into a fine thread between 2 centimeters and 1 inch, it is most likely AFB. If it does not rope, it is most likely EFB. However, the most accurate way to identify what type of brood disease is to send in a sample to USDA ARS Beltsville Diagnostic Bee Lab. The at-home tests produced by VITA are not widely available for individual purchase in the US, but may be procured through . ​
Sacbrood virus (SBV)
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Most visible at the pre-pupal stage at the end of the larval development. Exposed Infected larvae turn up towards the cell opening in a canoe-like shape and have conical heads. In early stages the larva will appear beige, then yellow and later turn to brown or black. If removed from the cell, larvae will remain intact and has clear liquid. You may also identify perforated or partially uncapped cells where bees have started to clean out infected larvae. ​
Parasitic mite syndrome (PMS)

​Infected larvae appear melted, however unlike foul brood, PMS larvae look snotty and milky. Colonies suffering from PMS may also have a low adult bee population, have observed deformed wings and have little activity at the hive entrance or lack of guard bees. The brood may be chewed down where bees have attempted to clean out the infected larvae. You may also see mites on the bees and larvae within the colony. ​
Shiny bees

​Shiny bees have lost their fuzz or tiny hairs. They may appear shiny and almost black. Shiny or black bees could be a sign of a paralysis virus infection within the colony.