Bee-keepers are faced with an imported pest that threatens honey production and crops that need pollination. Patricia Weston reports
You don't have to be large to have an impact. An insect the size of a grain of sand is causing serious problems for bee-keepers and threatens to reduce fruit yields, putting farmers under additional pressure.
Beehives across the country are succumbing to the varroa mite, a minute invader that can have a surprising influence on farming. "The mite Varroa destructor, until recently known as Varroa jacobsoni, is probably the most important present-day pest species of the honeybee Apis mellifera," says Dr Mary Coffey, a researcher at Teagasc in Clonroche, Co Wexford.
Varroa was discovered in the 1970s in North Africa, America and Europe; it spread to Britain in the 1990s. "It was first recorded in Ireland around 1998, and information from beekeepers suggest that it is now present in about 16 of the 26 counties," says Dr Coffey.
"The varroa mite enters the cells of developing honeybee larvae and lay eggs that hatch and develop to adults at a quicker rate than the honeybee larvae," she says. "The mites feed on the honeybee larvae, which either die or are much weakened. If the honeybee emerges as an adult, it will carry more mites, which infect further cells."
Once the mite infests, the bees are weakened and have a shorter life expectancy than unaffected bees, according to the Federation of Irish Beekeeping Associations. This reduces the amount they can forage and makes them more susceptible to infections that kill the colony. In severe infestations, emerging bees are deformed with stunted wings, shortened abdomens or both.
Dr Coffey's research into the varroa, which is still in its initial stages, hopes to establish whether Ireland has insecticide-resistant populations of the mite. She is also investigating the efficiency of drone-brood trapping as a non-chemical method of control. "This method, developed at the University of Wageningen, in the Netherlands, uses knowledge of the biology of the honeybees and mites."
Teagasc is also researching the possible use of organic acids, including formic, lactic and oxalic, as a means of control. "These acids, although naturally occurring in honey, in their concentrated form need formal testing of their efficacy and safety," says Dr Coffey. Patsy Bennett, an apiarist at Teagasc, says: "There are various ways of controlling the mite. Strips can be placed in the colony during August and September."
According to the beekeeping federation, the only chemical treatment approved for use in Ireland is Bayvarol, which comes as a plastic strip impregnated with a synthetic pyrethroid insecticide. Four strips are inserted into each brood box for 42 days.
"Mites can become immune to the strips, so other ways of controlling the mite have to be investigated," says Bennett. "Bee-keepers on the Continent use formic acid. Formic acid is a naturally occurring substance, so there is no residue or build-up on crops. Climatic conditions are different on the Continent than in Ireland, so Teagasc is researching the use of formic acid and various other methods to control varroa."
Ambrose Murphy, a bee- keeper from Co Wexford, handles his bee colonies on the assumption that they are infected by varroa. "I have been placing Bayvarol strips into my hives in September for the past two years," he says. "It is preventative. Varroa can spread when bees swarm or if a bee-keeper whose bees have the mite moves into your area. The varroa mite is countrywide, so beekeepers should be responsible and take precautions to prevent their bees becoming infected."
Infected honeybee colonies could have serious implications for crops if the spread of the mite is not controlled. "Bees are the most effective pollinators," says Bennett. "At Clonroche we have raspberries growing in polythene tunnels. In order to ensure pollination we place hives at the entrance to the tunnels.
"The strawberries we grow at Teagasc would be badly deformed and misshapen if it weren't for the bees that pollinate them," he says. "Bees are also important pollinators for oilseed rape."
Oilseed rape is a valuable cash crop, because of the food-grade oil it provides, but yields could fall if pollinators are not available. "Ireland would seriously lose out if the mite got out of hand," says Bennett.