Control of Chalkbrood in Vietnam

from Bees for Development Journal Edition 127 - June 2018

Notice Board

Nguyen Quang Tan

Chalkbrood disease has been known for many years by beekeepers with Apis mellifera in Australia, Europe, USA, and many Asian countries. It is caused by the fungi Ascosphera apis and Ascosphera alvei. The disease occurs when the larvae ingest the fungal spores with their food. Once digested, the spores develop inside the larvae’s guts and absorb the nutrients. Ultimately, the larvae die of starvation and form white or grey, chalk-like ‘mummies’ which give the name of the disease. The fungi reproduce by spores which can survive for up to 15 years. Each mummy can create millions of spores which stick to the adult bees, combs, frames, hives and pollen. The chalkbrood mummies are easily visible in the cells. It is not unusual for worker bees to remove and deposit them on the hive floor or at the entrance of the hive. Only in recent years has the disease been seen in Vietnam. It causes significant damage to the beekeeping industry: colonies are weakening, honey yields decreasing and production costs rising.

Chalkbrood in Vietnam

We recorded the following epidemic characteristics of the disease in Vietnam:

Infested honey bee species: There has been no recorded report of the disease in colonies of the Asian honey bee, Apis cerana.

Condition of the infested colonies: The disease usually occurs in weak colonies of Apis mellifera with a lack of food and/or a scattered brood pattern.

Age of the infested brood: The disease is mainly in the older larvae (4-6 days old) and prepupae (young sealed brood).

Time of outbreaks: The disease usually happens and causes losses in the rainy season when the atmosphere is very humid.

Spread of disease: This can be from one colony to another, from one apiary to another, or from one region to another by foraging and robbing bees, and by beekeepers: bee transport, exchange of combs and/or other equipment. Noticeably, the disease can be spread quickly and far by bees fed by the beekeeper with dried pollen collected from diseased colonies - unluckily dried pollen is commonly traded among Vietnamese beekeepers.

Level of disease spread: Chalkbrood has spread more rapidly than diseases caused by the mites Varroa sp and Tropilaelaps clareae. However, it is spread more slowly than Sacbrood, a viral disease which broke out in our Apis mellifera colonies about ten years ago.

Level of damage to beekeeping: This depends on the percentage of infested colonies and the situation of the diseased colonies, but in general Chalkbrood has caused severe economic losses for commercial Apis mellifera beekeepers.

**The author checking a colony for symptoms of Chalkbrood**
Photos © Nguyen Quang Tan

Controlling Chalkbrood

After some years suffering from the effects of this new disease, beekeepers have gained experience in its control, and the beekeeping industry in Vietnam is now recovering. Our experiences are:

• Keep bee colonies in good, healthy conditions: dense worker populations, strong queens and lots of food

• Always keep the inside of hives dry – cover hives to prevent rain getting inside, and place the hives sloping forwards so that water will run out if it does get into the hives. Also keep the floor of the hive free of debris from cocoons, food and wax.

Treatment for Chalkbrood

If there are only a few infested colonies occurring for the first time in the apiary, the beekeeper immediately destroys the newly diseased colonies - the bees and the frames are burned. Wooden hives can be used again if they are heat-treated with fire until the wood is burned brown to kill all the fungi.

If the beekeeper cannot do as above, s/he treats as follows:

• Make the diseased colony a mating colony: the queen is replaced with a queen cell. After the virgin queen comes out and then flies to mate, all the combs (with very little brood at this time) are taken out. At the same time, the diseased colony is moved to another hive. The hive from the diseased colony is placed in fire until the wood is burned brown. (The aim of boiling all the combs and placing the hive in flames is to kill all the fungi and their spores, so that we can harvest beeswax and the hive can be used again.)

• The mating colony is provided with good brood and food comb from a healthy colony. When the new queen starts laying eggs, the colony usually recovers from Chalkbrood.

• Spray the diseased colonies with a recommended vitamin C solution. This helps increase the tolerance of the colonies as well as to hold back fungal development.