The bioenergy crop Sorghum bicolor is a relevant pollen source for honey bees (Apis mellifera)

Abstract

AbstractAbundance and diversity of pollinating insects are decreasing. Intensification of agricultural bioenergy production is presumed to accelerate the decline of pollinators. Sorghum (Sorghum bicolor L. Moench) is a promising bioenergy crop. Enhanced dual‐purpose type cultivars have been developed and tested for suitability for bioenergy cropping in Germany. Sorghum is assumed to be a nutritional resource for pollen‐collecting insects. To evaluate this assumption, we studied the foraging strategy of A. mellifera colonies, which were migrated to sorghum fields in Germany. The bee hives were equipped with bottom fixed pollen traps. The pollen loads of the colonies contained variable shares of sorghum pollen ranging between approx. 10% and 50% (weight/weight). Sorghum pollen occurred frequently in more than 50% of all pollen samples. Experimental mini colonies were placed in plots which were grown with two varieties of sorghum, phacelia (Phacelia tanacetifolia), maize (Zea mays) and a control plot without any vegetation. All plots were encased with flight tents. Significant effects of the crop were found for the productivity parameters brood rearing and pollen collection. The sorghum and maize variants performed significantly better than the controls but significantly poorer than phacelia (p < 0.05). The parameters number of dead bees and colony sizes were not affected by the crops (p < 0.05). Pollen of sorghum is a valuable food for bees which supports nursing of bee brood, but its availability proved to be inferior to phacelia as the pollen shedding of sorghum lasted a considerably shorter time. Pollen collection by honeybees did not negatively affect seed yield of sorghum in any case. Under unfavourable weather conditions, flower visiting bees enhanced seed yield of sorghum.