A summary of an article written by Ingemar Fries and Henrik Hansen in 1993.

In two experiments, the influence from trapping comb tecnique on the natural mortality of mites from infested honey bee colonies was investigated in a Nordic climate.

Two apiaries, A and B, with 17 colonies each were used. The natural mortality of mites was followed in both apiaries from mid-May to mid-November with varying intervals between each counting. In apiary A a mesh bottom was used allowing practically all mites falling from the bees to be counted. In apiary B a plastic screen to collect mites, covering 53% of the bottom was placed in the center of the bottom board.

The first trapping comb was introduced on June 20 in apiary B, and June 21 in apiary A. The trapping device was a cage built from plastic queen excluders. In apiary A the method of Maul with nine days between each comb shift was used.

In apiary B, the intervals between each comb shift were seven days but with the third comb remaining in the cage without the queen until practically all brood was sealed nine days after the queen was released from the cage.

All combs that were removed from the colonies were marked with the colony number and placed in the deep freezer. Later all combs were uncapped and the mites washed out with a hand shower over a mesh and subsequently counted.

In apiary B, five colonies were managed to ensure that no sealed brood was present when the third trapping comb was removed. At this time, these colonies were treated with two applications of Perizin at two-day intervals and the mite mortality was counted.

In figure 3 and 4, the average daily mite mortality in apiary A and B respectively, is shown. Although, at slightly different levels, both apiaries show roughly the same pattern; a successive increase in the mortality level as summer proceeds, with a dramatic reduction when no sealed brood hatches in the colonies because of the brood removal.

The time required to complete the trapping comb method was estimated to 45-60 minutes/colony. No reduction in honey yield was noticed during the experiment, when there was no late honey flow.

The presented results support the hypothesis that the trapping comb system could be sufficient in a Nordic climate. This is contrary to the results presented by Maul, where the mite population in southern Germany, judged from the mite mortality, is allowed to increase substantially after the trapping comb period.