Glossary
A viral disease of honey bee larvae caused by Sacbrood Virus (SBV). Infected larvae fail to pupate, instead turning into fluid-filled sacs that eventually dry to a dark, gondola-shaped scale. Sacbrood is the most common viral disease of brood worldwide but is usually self-limiting in otherwise healthy colonies.
🌿 Field Note
During our spring inspections, we often see this firsthand. Understanding how our bees behave helps us make better decisions as beekeepers and better products from what they produce.
Sacbrood-infected larvae can be identified by their characteristic appearance. Affected larvae fail to shed their final larval skin before pupation, instead filling with a watery fluid and taking on a sac-like appearance. The color changes from white to yellow to gray-brown as the disease progresses.
Infected cells often remain uncapped as hygienic bees detect and attempt to remove diseased larvae. When capped cells do contain sacbrood larvae, the cappings are often punctured or sunken. Dead sacbrood larvae dry into a dark, brittle scale shaped like a Chinese slipper or gondola, which is easily removed from the cell unlike the ropy residue of American foulbrood.
Unlike American foulbrood, sacbrood rarely kills colonies and often resolves on its own within a few weeks. Strong colonies with good nutrition and hygienic behavior (bees that quickly detect and remove diseased larvae) typically manage sacbrood without beekeeper intervention.
If sacbrood persists or affects a significant percentage of brood, requeening with a queen from hygienic stock is the standard recommendation. Ensuring adequate nutrition (protein from natural pollen or supplements) also supports the colony's immune response. There is no chemical treatment for sacbrood.
Sacbrood is usually a minor, self-limiting disease. Healthy colonies with hygienic behavior clear infected larvae quickly. However, in already weakened colonies or during periods of nutritional stress, sacbrood can compound other problems and contribute to colony decline.
Nurse bees contract the virus while cleaning cells containing dead sacbrood larvae, then transmit it to healthy larvae through contaminated brood food. The virus can also be introduced through robbing bees from infected colonies or contaminated equipment.
The symptoms are different. Sacbrood larvae become fluid-filled sacs that dry to brittle, easily removed scales. AFB larvae become ropy and sticky, and dried scales are firmly attached to cell walls. Sacbrood also lacks the distinctive foul smell of AFB. However, if you are unsure, always contact your state apiary inspector for diagnosis.
From Our Hives
Our hives sit in the Bradenton, Florida sun. Every product starts with healthy colonies and careful stewardship.