The number of honey bee colonies fell by 16% across 36 countries in the winter of 2017-18, according to an international study.

It found that out of 544,879 colonies being managed at the start of winter, 89,124 were lost through a combination of circumstances including the effects of weather conditions, unsolvable problems with a colony’s queen, and natural disaster.

The study, led by a University of Strathclyde academic, surveyed 25,363 beekeepers across 33 countries in Europe – including the four nations of the UK – along with Algeria, Israel and Mexico.

Portugal, Northern Ireland, Italy and England experienced losses above 25%, while Belarus, Israel and Serbia were among those with loss rates below 10%.

Researchers found beekeepers who moved their colonies in the foraging season, to access other forage or for pollination, faced fewer losses than those who kept their bees in the same place.

Dr Alison Gray, a lecturer in Strathclyde’s Department of Mathematics & Statistics who led the study, said: “Loss of honey bee colonies is a highly complex issue. It tends to be influenced less by overall climate than by specific weather patterns or a natural disaster affecting the colony.

“We observe colonies in winter but what happens to the bees then can be partly determined by the conditions of the previous summer.

“Many are also lost when there are problems with a colony’s queen – for example, if she goes missing or is not laying the fertilised eggs which go on to become worker bees. Most colonies are also under attack from varroa mites, a parasitic mite.

“The impact of beekeepers migrating their colonies would be expected to be partly dependent on the distance travelled and the reasons for migration; this would be worth further investigation.”

The total loss rate overall was down from 20.9% in 2016-17 but was still higher than the 2015-16 figure of 12.0%.

The study had a focus on sources of forage, plants which bees visit to collect nectar and pollen, in six categories – orchards, oilseed rape, maize, sunflower, heather and autumn forage crops.

It has been published in the Journal of Apicultural Research and was carried out by researchers in the colony loss monitoring group of the international honey bee research association, which is based in the Institute of Bee Health at the University of Bern.