A sustainable and cost-effective tool to control the varroa mite may soon be available to New Zealand beekeepers thanks to the efforts of scientists at the Crown Research Institute, HortResearch.
Scientists at HortResearch have successfully bred honeybees that fight back against varroa - by suppressing mite reproduction.
Since its arrival in New Zealand seven years ago varroa has become the number one enemy of bees and beekeepers across much of the country. Able to reproduce and spread rapidly, the mite lays its eggs inside the brood cells of a beehive, where the mites develop to maturity by feeding on bee larvae.
Uncontrolled, varroa will usually ‘kill’ a bee colony within a year - an expensive loss to beekeepers as well as a major threat to New Zealand’s billion dollar fruit export industry, which relies on bees for pollination.
Varroa is currently controlled mostly through the use of chemical miticides - at an annual cost to industry of more than £500,000.
While such treatments are generally effective, their use is not sustainable said HortResearch honeybee scientist Dr Mark Goodwin. “Overseas, varroa has quickly built up resistance to these miticides, resulting in large hive losses. In addition, while perfectly safe if used correctly, beekeepers and growers would prefer not to have these chemicals in our natural environment,” he said.
With funding from the Sustainable Farming Fund, the National Beekeepers Association, individual beekeepers, and the kiwifruit industry through Zespri Limited, Dr Goodwin and his team have been searching for more sustainable ways of keeping varroa in check.
“We’re looking not only at controlling the mite more cheaply, but also at methods that meet the strong environmental and food safety goals of the bee industry and the horticulture industries it supports,” he said.
The idea to breed resistant bees came from overseas research that showed that varroa mites emerging from certain hives were unable to reproduce. This is due to a genetic trait in the bees themselves called ‘delayed suppression of mite reproduction’ or SMRD.
While SMRD is not yet fully understood, it appears to either render the mites sterile, or prevent them from developing reproductive capability. In nature the resistance levels only reach around 20 per cent because the resistance genes are constantly watered down through interbreeding.
Using bees carefully selected from around New Zealand, Dr Goodwin’s team have been interbreeding bees to increase the levels of SMRD within the population.
“With patience we’ve been able to breed bees whose hives render up to 80 per cent of varroa sterile. The problem is that the process is expensive and time-consuming. We could never rely on artificial insemination to supply the amount of bees needed to continuously replenish the resistance genetics of New Zealand’s 300,000 commercial beehives,” he said.
Instead, Dr Goodwin’s team hope that they can establish as self-sustaining population of high-resistance bees by keeping them isolated from non-resistant bees.
“An island was the obvious choice for this experiment and we were lucky that Sir Michael Fay and David Richwhite offered us the opportunity to work on Great Mercury Island, which lies off the coast of the Coromandel Peninsula.
“In fact they’ve done a lot more than just allow us access to the island. They’ve shown a real interest in the project and provided staff, equipment, transport and accommodation for visiting staff as well.”
Dr Goodwin’s team has now transported 50 high-resistance hives to the island, creating an instant population of 500,000 bees.
“Over the next few months those bees will breed and the population will reach around 2.5 million. We’ll be watching with interest to see if isolation allows these hives and their offspring to maintain a high degree of varroa resistance,” said Dr Goodwin.
If the experiment is successful the island, and possibly others like it, could become vital breeding centres for large numbers of highly resistant queens. These could then form the basis of a continuous flow of new genetics to the mainland, helping to maintain high levels of resistance in commercial hives.
