Pollination mix: honeybees and bumblebees as possible pollinators for Pyrus communis 'Conference'

Fruit crops such as apples and pears are often supplemented with honeybee colonies in the orchards to fulfil their pollination requirements. More recently, some growers intend to add bumblebees to increase the pollinator diversity and enhance the pollination process. In this study, the influence of bumblebees and honeybees on the fruit set, yield and fruit quality of Pyrus communis 'Conference' was investigated. Five different treatments were established, of which four were in cages: bumblebee (BB), honeybee (HB), a combination of both bumblebees and honeybees (Combi), a control with no pollinators (Control), and an open air treatment (Open Air). Trial design was a completely randomized block with five treatments, replicated three times. Pollinator activity and pollination intensity were recorded daily, fruit set was monitored during the growing season and fruit quality parameters such as fruit width, length, fruit shape, weight, brix, firmness, seeds and acid content of the fruits were quantified at harvest. Unlike the honeybees, the bumblebees flew very intensively from flower to flower and visited half-open and even closed flowers. This behaviour resulted in damaged flowers and a reduced fruit set in the cages with bumblebees. Fruit set at harvest was significantly higher in the HB treatment, whereas both the Combi and HB treatment had the highest seed set. Pears from the HB treatment had the lowest length/width ratio. The Control treatment had less pears with a normal ideal fruit shape. Overall, bumblebees were too active on the caged trees, damaging the flowers and negatively impacting fruit set. Honeybees on the other hand improved the fruit and seed set of 'Conference'.