Pests and diseases are certainly not the most popular topics beekeepers like to talk about - and so it comes as a surprise to many new beekeepers.
Bee brood diseases in their dormant form can exist in virtually every beehive. However, a strong and vigorous bee colony does not easily get affected - it is only when the colony weakens when diseases become an issue.
Constant monitoring for colony strength, pests, parasites and diseases is a vital element of successful beekeeping.
Brood diseases are caused by fungi, bacteria and viruses and can affect both sealed and unsealed brood.
The identification of brood diseases by their symptoms can be challenging and confusing - and some publications do in fact add to the confusion.
This publication by the Victorian DPI, AG0990 A Guide to the Field Diagnosis of Honey Bee Brood Diseases, is a field guide for apiarists to identify the four important brood diseases: American foulbrood, European foulbrood, chalkbrood and sacbrood. Apiarists are encouraged to submit samples for laboratory confirmation of their field diagnoses and to seek advice from Department of Primary Industries apiary officers.
This publication gets confusing when titles, text and referenced pictures don't match or lead to the wrong conclusion (Sacbrood is explained under the title Chalkbrood, and a description of chalkbrood does not exist, apart from two photos)
A good reference is this publication from the DPI in Queensland - Chalkbrood - it clarifies the confusion around the identification of brood diseases.
In general, the appearance of a healthy brood pattern is regular with no dead larvae or pupae. Each cap is slightly raised or convex, without any holes. Caps are uniformly brown, tan or cream.
Note: the empty cells in between the capped are "heater cells" and not a sign of a problem.
Larvae are glistening and pearly white. Healthy pupae under the caps are at first white but as they develop into adults, their colour darkens. The eyes begin to colour first.
Common brood disease symptoms
A symptom common to all bee brood diseases is perforated cell caps, or cell caps completely opened or removed. It is an indication that something is wrong with the capped brood. Some publications describe this as a symptom for AFB, but this symptom is common to all diseases that result in dead brood behind capped cells, even chilled brood that died without a disease.
When the expected hatching of bees from the pupae is overdue the adult bees start opening some of the capped cells to interrogate.
Brood Disease Management
Hive Examination - Examination of brood frames and floor debris is required especially in spring. Bees should be gently shaken from the frames to allow full inspection, abnormalities are then easily spotted.
Vigilance is important with all honeybee diseases. Check all colonies regularly for health and suspect any colonies that are not thriving where there is no already known reason. Colonies that die out should be examined thoroughly and sealed to prevent robbing and spread of any disease present.
Diseases have a more serious effect on weakened colonies. Prevention is the best method of controlling diseases by maintaining healthy, strong and vigorous colonies that display good hygienic traits.