The Varroa mite is a parasite of the honeybee. Being a mite it is not an insect; it has eight legs and is a member of the spider family. As parasites go, Varroa mites are quite large in comparison to the host – about the size of a pin head and quite easily visible to the naked eye. If humans had a parasite the same relative size of Varroa it would be about the size of a saucer. The mites have a reddish brown, leathery shell and from above they look a bit like a crab but without the pincers.
The reason European honeybees (Apis mellifera) are so damaged by the Varroa mites and so unable to cope with them is that Varroa evolved far away to the east, in Asia and on a different host species of bee – the Asian honeybee (Apis cerana). The Asian honeybee has evolved defences against the mite over thousands of years but European honeybee has no defence – except the beekeeper.
However, it was beekeepers who also facilitated the epidemic. The movement of bees by humans first allowed the Varroa mite to cross species to A.mellifera, then infested colonies of bees were moved back into and across Europe allowing the mite to spread throughout in a very short time. Varroa reached the UK in 1992 and was found in Ireland in 1998.
Varroa and the problems associated with it have been the scourge of beekeeping ever since and seem unlikely to be solved any time soon.
The life cycle of Varroa is horrible:
- In spring the queen bee starts to lay eggs and when these hatch into larvae, the adult Varroa which have overwintered by feeding on adult bees get into the open cells and hide. They prefer drone larvae but will also get into worker brood.
- As soon as the cells are sealed, the Varroa (which are already pregnant) lay their eggs beneath the larvae – each lays 1 male egg and 4 or 5 female eggs.
- The adult female mite then punctures the young bee larva and begins to feed from it. When the young mites hatch, they too feed from the same site. The effects of feeding weaken the larvae but the mites also pass on viruses through their mouthparts, one of which interferes with development and causes the wings to become deformed.
- The first mite to hatch is the male and as his sisters hatch he mates with them. When the poor deformed little bee chews its way through the capping all the pregnant young Varroa run out with it into the hive – each one starting the cycle over again.
There are direct and indirect effects from Varroa infestation. Direct effects include:
- The larvae are obviously directly weakened by the mites sucking their baby-blood;
- Young bees hatch with horribly deformed bodies and are evicted from the hive by the adults;
- Many young bees have shrivelled wings from a virus passed on by the mites;
- Other bee viruses which might otherwise have minor effects on the colony are vectored by the mites so they become threatening epidemics;
- Drones can be affected in different ways if they survive at all, they are smaller in size so their virility and fertility are also diminished.
Colonies of bees infested with Varroa die out within 3 years at the most. There are no wild bees left in either the UK or Ireland. Any bees living in the wild are recent escapes from a beekeeper and will die soon. This is very important indeed for many reasons but one major effect of the extinction of wild colonies means there are fewer drones out there for the queens to mate with. Coupled with the appalling weather this has resulted in major problems caused by poor queen mating.
Beekeepers are working on breeding bees that are resistant to the Varroa mite. This is the best solution to the problem and bee breeders are having success but at the moment that one is for the future.
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