Floral reward and insect visitation in ornamental deutzias (Deutzia spp.), Saxifragaceae sensu lato
Marzena L. Masierowska
Ornamental plants cultivated in urban regions may help to sustain local pollinator populations as well as broaden food source for honey bees. This 3-year study examined the abundance of flowering, nectar and pollen production as well as insect visitation to six ornamental Deutzia species and cultivars. In Poland, the blooming of the observed taxa lasted from early June to the end of July. The number of developed florets strongly depended on the weather conditions before and during the flowering period. All deutzias showed abundant secretion of highly concentrated nectar. The mean amount of sugars secreted in nectar per 10 flowers ranged from 11.8 mg (D. scabra) to 18.7 mg (D. gracilis). Average pollen mass produced by the same number of florets was similar in all species and reached 17.8 mg. The highest estimated nectar (71.1 g) and pollen (74.1 g) crop per plant was obtained from D. scabra cv.Watereri. Deutzia flowers attracted numerous insects, mainly honey bees, bumble bees and solitary bees. The species and cultivars investigated are highly valuable honey plants. Increased use of these shrubs in gardens and parks should be encouraged in order to enrich nectar and pollen pasture for honey bees and wild Apoidea. However, their use is limited to areas of mild climate and adequate water supply.