A colony inactive in mid-February: which diagnosis is most likely?
One of your colonies is inactive in mid-February. It had produced a good harvest the previous year. On opening it, you find that the colony is dead: the number of dead bees on the frames and on the hive floor is low, the brood is patchy, and the food stores are still clearly present.
- Colony died of cold.
- European foulbrood.
- Varroosis.
- American foulbrood.
- Colony died of starvation.
- Drone-laying colony.
Show answer
Correct answer: 3.
Varroosis.
Why?
The picture described typically corresponds to a colony that collapsed during the winter after a heavy infestation by Varroa destructor. The food stores are still present, which makes death by starvation less likely. The small number of dead bees in the hive also suggests that some of the bees left the colony before it died out completely.
Patchy brood, perforated cappings, dead bees partially protruding from the cells, and whitish traces of varroa faeces on the cell walls can reinforce this diagnosis. The diagnosis nevertheless remains an overall interpretation: one must always take into account the history of the apiary, the varroa monitoring carried out, and the treatment applied the previous summer or autumn.
What you need to understand
Varroosis is a major parasitic disease of the honey bee. It weakens the bees, disrupts the brood, and promotes the transmission of viruses, particularly when the infestation increases sharply in late summer.
A colony may still appear productive during the nectar flow and then collapse later if the varroa pressure has not been reduced sufficiently in time. This is why a good harvest the previous year does not guarantee a good capacity to overwinter.
Key takeaways
A colony that has died in winter with stores present, few dead bees, and patchy brood strongly suggests a varroosis problem, especially if the infestation monitoring or the summer treatment were insufficient or carried out too late.
Prevention relies on a varroa management concept pursued throughout the year: infestation monitoring, treatment at the right time, compliance with authorized products, and regular renewal of colonies able to overwinter properly.