Kakugo Virus

Kakugo virus is a virus reported to occur in the brains of guard bees that attack hornets in Japan. Genetically it is almost identical to deformed wing virus (DWV) and is today regarded as one of its strains. For the beekeeper the meaning is clear: it has no symptoms or medicine of its own and, like DWV, it is managed through varroa control.

What is it?

Kakugo virus was described in 2004 by Japanese researchers. They reported finding this virus in the brains of guard bees that attacked hornets (Vespa), but not in the calm bees of the same colony. The name comes from a Japanese word meaning "resolve, readiness".

Later genetic studies showed that Kakugo virus is very highly similar (about 98%) to deformed wing virus. For this reason it is today treated not as a separate disease but as a strain (variant) of DWV.

The aggression claim

The idea that the virus makes bees aggressive is intriguing, but it has not been proven. DWV can also be found in the brains of other bees, and later studies did not show a consistent cause-and-effect relationship between the virus and aggression. There is no basis for attributing aggression in a colony to this virus.

Common misconceptions

• There is no "natural remedy" or "vaccine" against Kakugo virus; products sold under this name are misleading.
• Specific effects such as reducing the queen's laying or causing developmental defects in larvae have not been proven.
• Kakugo cannot be told apart from DWV in the field; the distinction can only be made by a molecular laboratory test, and in practice there is no need for it.

What does the beekeeper see in the hive?

There is no field symptom specific to Kakugo. The picture you may see is that of deformed wing virus:

• Young bees with crumpled, short, useless wings
• Bees with short, swollen abdomens that die early
• Varroa mites on the bees; perforated cappings, uncapped (bald) pupae
• Rapid weakening in late summer and autumn, colony loss in winter

How to confirm it

The virus cannot be seen with the naked eye; Kakugo and DWV can only be distinguished by a molecular test. This distinction does not change your hive management. What you really need to measure is the varroa level: use an alcohol or icing sugar wash, or a counting board under a mesh floor.

What to do

1. Do a varroa count. Count immediately in every colony where you see bees with crumpled wings.
2. Treat if the threshold is exceeded. Use an authorised varroa medicine, following the label instructions. Active substance groups: organic acids (oxalic, formic), essential oil components such as thymol, and synthetic acaricides. During the honey flow and with honey supers on the hive, do not use unsuitable medicines; do not use the same active substance continuously.
3. Protect the winter bees. Late-summer treatment must be completed before the winter bees are raised.
4. Support a weakening colony. Check that food and pollen are sufficient; reduce the entrance against robbing.
5. If the problem recurs every year, requeen. Prefer calm lines with strong hygienic behaviour.

There is no authorised medicine against the virus; antibiotics do not work and leave residues in honey.

Prevention

• Monitor the varroa level regularly throughout the year; act on the count, not just the calendar.
• Treat all colonies in the apiary at the same time; an untreated hive reinfests its neighbours.
• Reduce robbing and drifting; do not leave weak and collapsing colonies unattended in the apiary.
• When buying bees and queens from outside, choose sources whose health status is known.