Honeybee floral constancy and pollination efficiency in sunflower (Helianthus annuus) crops for hybrid seed production

Abstract

Honeybee Apis mellifera are considered essential pollinators in sunflower (Helianthus annuus) crops for hybrid seed production where they have to transfer pollen from male fertile (MF) to male sterile (MS) cultivars. Despite their biased preference for specific resources defined as floral constancy, it is unknown how they behave in hybrid sunflower seed crops exhibiting a noticeable dimorphism between parental lines. We studied honeybee foraging behavior in sunflower crop fields that exhibited a variable dimorphism among parental lines. Our results suggest low honeybee efficiency in terms of foraging flights between parental lines, since lower switching frequencies from MF to MS lines were observed for cultivars with increasing dimorphisms. Moreover, we also captured bees on MS capitula and at the hives to quantify the sunflower pollen grains adhered to their bee bodies with the aim to determine mechanisms responsible for the transfer of pollen between parental lines in cultivars with dimorphisms. Results show that honeybees located at the hive entrance, performing guarding and/or food receiving tasks, could act as agents facilitating pollen transfer between returning foragers and those that take off. This issue could partially compensate the low honeybee pollinating efficiency in terms of flights between parental lines.