A little mite, like a tiny spider the size of a pin head, has been plaguing New Zealand’s bee industry. The mites, called varroa, are parasites which live on the outside of honey bees and their developing larvae. They feed on the bees and lay their eggs on the larvae, often causing death or deformity to the developing bee. The mites’ activity weakens and kills honeybee colonies. This represents a serious threat to our entire economy because the bees are responsible for pollinating many of our food crops.

The varroa mite is a problem in many parts of the world. No one is sure how it came to New Zealand as it can only be spread from live bees to other bees, and we have not allowed bee imports into this country for more than 40 years. It is likely that the infestation was a result of an illegal import of queen bees from a varroa-infested country, or an accidental import of a bee colony or swarm in a shipping container.

But help for the bees might be at hand, scientists have been investigating a fungus that may well turn out to be the mite's 'worst enemy'. Honeybee researchers at Plant & Food Research (PFR) have successfully used a strain of the common insect fungus Metarhizium to treat beehives infected with varroa. Metarhizium is a very common fungus that occurs naturally in the environment. Harmless to humans, it is known to infect a large number of insects and has previously been used as a biocontrol for plant pests.

Using the fungus to combat varroa is not new. Previous attempts to develop a commercial Metarhizium-based product have failed because the fungus is rapidly removed from the hive by the bees themselves as part of their normal hive cleaning and maintenance behaviour.

Honeybee expert Dr Mark Goodwin says his team have solved this problem by finding a way to keep the fungus within the hive at high enough concentrations to achieve mite control.

"It was enormously frustrating. This strain of Metarhizium is varroa's worst enemy. So we had an excellent biocontrol for varroa but were being thwarted by a bunch of very house proud bees," says Dr Goodwin.

"We said to ourselves, 'This is a biological product. We need to stop thinking of it as a pesticide treatment and more as a living organism'. When we did that we found a way to make Metarhizium part of the overall hive ecosystem. The bees accept it, and the fungus is able to get on with killing varroa."

Plant & Food Research has applied to patent a device that positions the fungus at the entrance and exitways of beehives. The bees come into contact with the fungus as they enter or exit the hive.

Great Mercury Island breeding programme

Plant & Food Research established a varroa resistance-breeding programme on Great Mercury Island.  The island, located 8 km off Coromandel Peninsula is free of feral bees. PFR and Rainbow Honey are breeding queens selected for a trait known as varroa-sensitive hygiene (VSH). VSH bees should enhance tolerance to the general bee population and reduce the levels of varroa infection.

Awards for Dr Mark Goodwin

Dr Goodwin is recognized as a world leader in the field of honey bees and crop pollination practices. In 2009, he received the New Zealand Science and Technology Medal, awarded by the Royal Society of New Zealand. In 2016, Dr Goodwin received the inaugural Apiculture New Zealand Peter Molan Award.

Learn more about Dr Goodwin's work with pollination in the articles Kiwifruit pollination problems and Avocado pollination.

    Published 2 September 2008, Updated 28 September 2017