Nectar and Pollen Production and Insect Visitation on Ornamentals from the Genus Hosta Tratt. (Asparagaceae)

Properly arranged ornamental gardens in both urban and agricultural landscapes can be of a benefit to bees. In this study, we observed the flowering phenology, nectar, and pollen production of the ornamental Hosta species and varieties (H. sieboldiana Engler, H. capitata Nakai, H. crispula Maekawa, H. fluctuans Maekawa, syn. H. sieboldiana var. fluctuans hort., H. undulata var. univittata Miquel (Hylander), syn. H. univittata). Our experiment was conducted in the 2012 - 2014 time period, at the UMCS Botanical Garden in Lublin, Poland (51° 14’ N, 21° 34’ E). The total sugar yield varied almost 5-fold among Hosta ornamentals; the lowest amount was calculated for H. fluctuans (2.31 g per 10 m²) and the highest for H. capitata (11.80 g per 10 m²). The average pollen yield was from 0.24 g per 10 m² (H. undulata var. univittata) to 9.53 g per 10 m2 (H. capitata). Pollen grains were bilaterally symmetrical, and large-sized. In polar view, they were prolatum (shape index 1.33 - 1.61), while in equatorial view, oblatum (shape index 0.5 - 0.7). Hosta species can complete the summer pasture mainly for bumblebees. In four of the five Hosta representatives, bumblebees accounted for 60 - 70% of the total visits. The honeybee predominated only on the flowers of H. capitata (54 - 71%). Solitary bees were rarely observed (3 - 9% of visits). The phenotypic traits of Hosta flowers (the accumulation of nectar in the deep and narrow perianth tube) reduced the access to nectar reward and restricted an array of insect visitors.