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Concerns over varroa mite resistance
The spread of a pesticide-resistant mite, which can decimate honeybee hives, is causing concern among beekeepers in New Zealand.

Dr Mark Goodwin of the New Zealand Institute for Plant & Food Research says while Varroa destructor has been in New Zealand for ten years, they've only recently found evidence of resistance to the synthetic pyrethroid treatments used to control them.

"Last October a hive near Auckland tested positive for pesticide-resistant Varroa, but we don't have a handle on how far this resistance has spread", he says.

"The problem with this is that beekeepers have to decide now what chemical to use for the autumn treatment of their hives."

In New Zealand, beehives are routinely treated for Varroa in autumn and spring with one of three registered chemicals.

"Two of the three chemicals are synthetic pyrethroids, which have a similar mode of action," says Goodwin.

He recommends that beekeepers alternate the use of one of these chemicals with an antiparasitic drug to prevent resistance developing, but admits it's hard to get the message out there.

Pesticide-resistant Varroa mites may also be spread through the introduction of queen bees or worker bees, but it's typically by infected bees drifting from hive to hive.
Rapid spread

The agricultural industry relies on bees for pollination of food and pastoral crops, as well as for honey and beeswax. Hives are regularly transported around the country to pollinate seasonal crops, an industry estimated to be worth NZ$3 billion (A$2.4 billion).

In 2009, the Ministry for Agriculture and Fisheries lifted all bans restricting the movement of bees after discovering the widespread presence of Varroa in the South Island.

Goodwin says that the free movement of hives will allow chemically-resistant Varroa to spread much more quickly throughout the country and that there's likely to be a significant increase in the annual hive death rate from its current level of 5%.

"It is hard to know exactly how high this figure could escalate, as it is down to the individual beekeepers to monitor their colonies and ensure treatment protocols are adhered to," he says.
Precautionary measures

Goodwin also believes that among beekeepers, particularly hobby beekeepers, there's a lack of awareness of and preparedness for dealing with Varroa resistance.

Jane Lorimer, a former president of the National Beekeepers' Association of New Zealand, keeps more than 1000 commercial hives in the Waikato region. She alternates between pesticides and carries out oxalic acid treatment during winter, but admits it will become more difficult.

"We [still] expect to see resistance at some point."

Pesticide importer Peter Lyttle, says several beekeepers around Auckland, Tauranga and the southern part of the North Island have found their spring treatment to be less effective than in previous years.

While scientific tests have not been carried out, it's possible that these hives could contain Varroa that are resistant to synthetic pyrethroids.

"We've noticed that autumn sales of [antiparasitic strips] have doubled in comparison with the same period last year", says Lyttle. "As yet, even in countries like France where they have been used since 1995 there have been no reported cases of resistance," he says.

For now, Australia remains the only major bee-keeping region in the world where Varroa has not yet been found. But most experts agree that it is just a matter of time before it arrives, most likely by hitching a ride into one of the ports.

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