Honeybee pollination of sunflower cultivars Hysun 30 and Sunfola

Abstract

In trials on an irrigated crop of hybrid sunflowers, (Helianthus annuus), cv. Hysun 30, in northern Victoria, plots where bees had access produced 11 % more seed than plots where bees and larger insects were excluded. Although some seed was set in cages by airborne pollination and self-pollination, honeybees increased seed set significantly. There was a slightly greater oil content in seed from open plots but no difference in weight of 1000 seeds or percentage germination. There was a 20% increase in the percentage of flowers that set seed in the open compared with enclosed plots. There was a 1362% increase in open-pollinated flowers that set seed compared with self-pollinated, but there was no difference between open-pollinated and open-pollinated supplemented by hand-pollination. The yield of seed from open plots of the so-called 'open-pollinated' cv. Sunfola was directly related to the honeybee density on the crop, expressed as ratio of bees to inflorescences. Honeybees were effective cross-pollinators of the sunflowers. Hysun 30 pollen was not attractive to bees and they tended to discard it. Colony strength declined while the bees worked the crop. The data suggest that a rate of one honeybee per plant during anthesis could optimize yields of set seed.