Breeding a better bee

Thu, Apr 19, 2012, 01:00

Bees are under threat from a species of mite, but beekeepers in Tipperary are breeding bees that can resist the parasite, in an effort to save the prolific pollinators from extinction, writes EOIN BURKE-KENNEDY

BREEDING COLONIES of disease-resistant superbees to safeguard the pollination of vital food crops sounds like the stuff of science fiction. However, it’s a strategy that is fast becoming a reality in some countries, and one that is soon to be adopted here.

It’s seen by some experts as the only long-term solution to a plague that is wiping out honeybee populations across the globe. Nature’s most prolific pollinators have been struggling to cope with the ravages of a tiny blood-sucking parasite known as the varroa mite. The crab-like mites attach themselves to bees, acting as vectors for several lethal viruses to enter the bee’s body and spread infection through hives.

In a little more than two decades, the mites, in combination with other viruses, have killed off up to 30 per cent of Europe’s bees, and a whopping 85 per cent of Middle Eastern bees.

In the US, mite infestation has been linked to the phenomenon of “colony collapse disorder”. It has seen bee numbers drop by more than a third, and the country’s once-robust honey industry has been decimated.

Since they arrived on these shores in 1998, the mites have almost entirely wiped out Ireland’s population of feral honeybees, leaving bees from managed hives and other pollinating insects to fill the vacuum. The sight of wild bees swarming in old tree trunks or household cavities, once a common part of summer, is now largely a thing of the past.

While managed hives can be successfully treated with bee-friendly pesticides to control the problem, the mites have become increasingly resistant to the chemicals in the pesticides, hence the need to consider more novel ways to tackle the problem.

The Tipperary-based Galtee Bee Breeding Group has begun a five-year project to develop a colony of “designer bees” which are capable of tolerating mite infestation. Micheál Mac Giolla Coda, apiary manager with the group and one of Ireland’s leading experts on beekeeping, says the plan is to harness the bee’s natural defences against the mite. Certain bee colonies, he explains, have adopted a grooming behaviour to counteract the varroa, which involves biting off each other’s mites.Similarly, other hives appear to exercise tighter hygiene controls, ridding the colony of varroa-infected larvae, which breaks the breeding cycle of the mite.

The problem is that different colonies and even individual bees within the same hive display varying levels of these behaviours. The Galtee group’s task is to select and cross-breed the bees with the most advanced grooming and hygiene habits.

In the UK, scientists, using observational hives in which bees are individually numbered, have traced superior grooming behaviours to individual drone patrilines (male lineages) using DNA markers.

The Galtee group is, however, planning a more basic screening process in simply identifying the hives with the best mite-attrition rates. This will be done, Mac Giolla Coda says, by observing the number of damaged mites and discarded mite-affected pupa parts that fall from the hive on to specially placed observation trays. By selecting for these behaviours, the group hopes to breed a strain of bees that is more adept at coping with the mite, a practice that has been successfully carried out in other countries.

When 60 per cent of the “natural mite fall” exhibits signs of having been intercepted by grooming, studies show the hive no longer needs to be treated with miticide; in other words, the bees are adequately dealing with the problem on their own.

“We hope to produce strains of disease-resistant and mite-tolerant bees which we can eventually return to the wild,” he says.

It is difficult to overstate the honeybee’s importance as a pollinator in the wider ecosystem. The Food and Agriculture Organisation of the United Nations estimates that of the 100 crop varieties that provide 90 per cent of food worldwide, 71 rely to some extent on bee pollination. In Europe alone, 84 per cent of the 264 crop species are pollinated by bees and other animals. According to a major UN-sponsored report published last year, the work that bees, butterflies, birds and beetles do provides the world’s economy with about €154 billion each year.

In 2011, the Galtee group completed a five-year nationwide survey of Irish bees which identified the dark European honeybee – Apis mellifera mellifera – as the predominant strain of honeybee in the country. Rather than importing similar disease-resistant varieties of this bee, the group has a strict policy of not taking in bees from abroad so as to conserve the purity of the native strain. It was the cross-breeding of African and European honeybee subspecies which resulted in the notoriously aggressive Africanised hybrids, known colloquially as “killer bees”.

Apart from the varroa blight, honeybee populations have been under pressure globally on a variety of fronts, not least the gradual disappearance of the insect’s natural flower-rich habitat as a result of more intensive farming. Pesticides are also a problem. Two recent European studies suggested the use of common agricultural pesticides, which were originally viewed as harmless to bees, could be disrupting the bees’ homing systems, causing them to get lost and perish. This may be a contributor to colony collapse disorder.

The decline in bee populations in some parts of the world has been so rapid that some experts fear that the vital pollen-gathering insect may be on a trajectory towards extinction. Some Chinese farmers have had to resort to pollinating fruit trees by hand because of the lack of insects.

Swarmageddon: Tiny mite with big bite

Varroa mites are now the single biggest global killer of honeybees. They were first found in Asia in 1904 but in recent decades have spread to all continents bar Australia.

The brown crab-like parasites drill holes, usually in the bee’s back or abdomen, to drink its blood while injecting viruses to suppress the bee’s immune system, leaving it vulnerable to disease. They have a distinct preference for drone blood but also prey on worker bees and their larvae.

They first appeared in Ireland in 1998 and are blamed for wiping out the country’s feral honeybee population as well as many small, old-fashioned beekeeping operations.

Just 2,500 mites are enough to overwhelm a colony of 60,000 bees. The mites spread from colony to colony by drifting workers and drones within an apiary. Most infested colonies die within one to two years if the beekeeper does not take suppress the infestation.

While treating hives with miticides has been effective in controlling the problem, the mites are increasingly becoming resistant to the chemicals used in these treatments.

Certain bee colonies have adopted more advanced grooming and hygiene behaviours to counteract their mite problem. Beekeepers in Ireland are hoping to enhance these natural defences through selective breeding.

The population of honeybees in Ireland in terms of numbers is difficult to assess but the Federation of Irish Beekeepers’ Associations estimates that its 2,500 members in the Republic have an average of 10 colonies each.

This suggests there may be about 25,000 colonies with 30,000-60,000 bees in each. In the North, the various associations are thought to encompass a further 1,000 beekeepers or a further 10,000 colonies.