Contribution of managed honeybees (Apis mellifera scutellata Lep.) to sunflower (Helianthus annuus L.) seed yield and quality

Abstract

Insects are considered to be responsible for 80-85% of all pollination, with honeybees being well known for their pollination services for many crops. The effect of managed honeybee pollination on sunflower seed yield and quality (germination percentage and oil content) was investigated at the University of Pretoria experimental farm and in commercial sunflower fields at Settlers. This was done through pollinator exclusion and pollinator surveys on sunflower field plots located at different distances from managed honeybee colonies. Observations on the foraging behaviour and activity of honeybees throughout the day were also made. The data presented in this thesis reveal that seed quantity and quality of sunflower increased significantly as a result of insect visits. Insect pollination improved the mass of 100 seeds (by 38%), as well as their germination percentage (by 38%) and oil content (by 36%). Moreover, visitation frequency, seed yield and quality were negatively correlated with distance to the honeybee hives, suggesting that the distribution of honeybee colonies is not enough to maintain an adequate pollination service throughout the large sunflower fields at Settlers. Honeybee foraging activity varied throughout the day, the highest activity being from 9h00 until 16h00, and activity was correlated with temperature. The results of this study suggest that the use of managed honeybees in sunflower crop production can effectively increase the seed quality and quantity, but additional management measures should be considered to improve production in large monocropping farms that are currently isolated from pollinator sources. Additional provision of honeybee colonies is needed in sunflower production areas during the flowering period. Furthermore, as our results show that in the presence of pollinators other than honeybees seed yield was also improved, management measures that promote the biodiversity of sunflower visitors may also have an important contribution.