Honey bee losses during mowing of flowering fields

Published source details Fluri P. & Frick R. (2002) Honey bee losses during mowing of flowering fields. Bee World, 83, 109-118.
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This study is summarised as evidence for the following.

	Action	Category
	Increase the use of clover leys on farmland Action Link
	Use mowing techniques to reduce mortality Action Link
	Plant dedicated floral resources on farmland Action Link
	Plant nectar flower mixture/wildflower strips Action Link

Increase the use of clover leys on farmland

Fluri & Frick (2002) rotary mowed white clover crops during flowering with and without a mechanical processor, and monitored the death and injury to actively foraging honey bees Apis mellifera, on two 0.33 ha trial plots in Switzerland. During mowing with a rotary mower and processor (which crushes mowings to accelerate drying), 53-62% of the number of foragers recorded before mowing were found injured, dead or otherwise stuck in the mown grass after mowing. When mowing was conducted without a processor, the average number of bees left dead or unable to fly was reduced from an average of 1.4 bees/m2 (with processor) to 0.2 bees/m2 and many bees were observed foraging or flying away after passing through the mower. The effects of mowing with a processor (but not without) were also tested on a similar-sized plot of Phacelia tanacetifolia, on which bumblebees were recorded as well as honey bees. On average, 0.2 foraging bumblebees/m2 were recorded before mowing, and 'practically' no bumblebees were found in the mown grass.
Use mowing techniques to reduce mortality

A replicated trial in Switzerland from 1996 to 1999 (Fluri & Frick 2002) found seven times more honey bees Apis mellifera were killed or unable to fly when white clover Trifolium repens plots were mown with a rotary mower and mechanical processor (which crushes mowings to accelerate drying) than without a processor (14,000 vs 2,000 honey bees/ha dead or unable to fly respectively). The height of flowers in relation to mower height affected bee survival. Honey bees foraging on phacelia Phacelia tanacetifolia flowers taller than the upper edge of the mower (70 cm) were shaken off and able to escape. Bee losses were higher on two white clover plots where the flower height was 25-30 cm (53% and 62% bees lost after mowing) than on one phacelia plot (flower height not given, but taller than the mower) (35% bees lost). Mowing speed did not have a significant impact on bee losses. Three plots were located on one trial farm, plots measured approximately 0.3 ha. One plot was sown with phacelia in 1996. Two plots were sown with 50% white clover in 1998 and 1999. Five to six honey bee colonies were established adjacent to the plots several days before surveying. Plots were mown with a 1.8 m-wide drum mower with integrated conditioner fixed to the side of a tractor. In 1999 the clover plot was mown with and without the processor. The number of bees before and after mowing was recorded in 1-4 m² quadrats.
Plant dedicated floral resources on farmland

Fluri & Frick (2002) recorded 0.2 bumblebees/m2 (2,000 bumblebees/ha) foraging on a single 0.3 ha phacelia plot in Switzerland.
Plant nectar flower mixture/wildflower strips

A replicated trial in Switzerland from 1996 to 1999 (Fluri & Frick 2002) found 26 honey bees Apis mellifera/m² and 0.2 bumblebees Bombus spp./m² foraging on a plot sown with phacelia Phacelia tanacetifolia in 1996. Two plots sown with 50% white clover Trifolium repens, one in each of 1998 and 1999, had 1.7 and 3.9 foraging honey bees/m² respectively. All three plots were located on one trial farm, plots measured approximately 0.3 ha. Five to six honey bee colonies were established adjacent to the plots several days before surveying.