Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

Slowing varroa’s deadly march

The varroa bee mite has caused significant damage to New Zealand’s honey production since it was first discovered in 2000 but research has highlighted unique aspects of the mite’s biology and behaviour that could be used in the fight against it.

Varroa, an external parasite of honey bees transferred to new bee colonies on adult bees, is reducing the number of bees in managed hives as well as feral or wild colonies. This has an impact not only on the beekeeping industry, but it is also potentially damaging for crop pollination and pollination of pasture legumes.

During 2003 and 2004 while undertaking MAF-funded research into the behaviour, biology and interaction of the mite with the honey bee researcher Zhi-Qiang Zhang and his associate Dr Q.H. Fan noticed an interesting behaviour of the mite while it develops.

The mother mite gets into the hive attached to the body of the honeybee and just before the worker bees cover the cells to protect the larvae, the mite enters. There it lays several eggs — the first one being a male — on the upper surface of the cell, where its offspring grow and mate. They feed on the immature bee lying on the bottom of the cell and return to rest on the upper surface of the cell. After three weeks, the matured female offspring and the mother mite attach to the bee when it emerges.

‘I noticed this behaviour of varroa mites staying on the top surface of the cell maximizes their survival within a small space, where the enlargement and movement of the growing bee could have interfered with their way of live if the mite had not this special adaptation’ Dr Zhang says.

That simple observation led to an equally simple idea — what would happen if the cell was turned upside down? Dr Zhang believed the mites could get confused and crushed, and secondly, the male and female mites would not be able to find each other to breed.

‘So we undertook some simple experiments of flipping the panels upside down inside the hive and we found there was a 50% death rate for mites when we did this on a weekly basis.’

Working with beekeeper Neil Furness during his Royal Society Teacher Fellowship, Dr Zhang tested the methods in a replicated field test during 2008. He found significantly reduced number of varroa in rotated hives than un-rotated ones, and when treatment started when the mite number was low in the hive, this method alone can save the colony from being destroyed by the mites.

Nobody had realised how a simple adjustment could cause such significant destruction of the varroa mite but the issue is now turning the idea into a prototype hive that is workable for beekeepers. This would be based on the existing rectangular beehive but with a mechanism to rotate it as and when required.

‘The idea is simple but making it work is more challenging,’ Dr Zhang admits.

‘In the short term it is cheaper for beekeepers to use chemicals to manage varroa but the problem is this will induce resistance. Furthermore, using chemicals to control varroa is not the best for our “clean green” image.

‘Development of a specialised hive is not a cure, it’s another tool in the toolbox. But, it certainly looks promising,’ Dr Zhang says.

After all, there is a lot at stake; the agricultural industries major contribution to the New Zealand economy is the pollination of plants, which is worth many times the value of honey and other bee products. One third of the volume of our food is reliant on animal pollinators, not just honeybees and three quarters of the diversity of our food is dependent on animal pollinators. Therefore, if we lost pollinators then we would have a restricted and less healthy diet.

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