Bumblebee pollination activity in a commercial tomato greenhouse during the winter season

Bumblebee activity interaction with solar irradiation, solar irradiation and HPS lighting irradiation, the HPS effect of photoperiod, day temperature and hive density were assessed with tomato fruit weights in a commercial tomato glass greenhouse in 2020–2021. Pollination activity was measured by observing ten randomly chosen cv. ‘Beorange’ tomato plants and by counting bumblebee bruised tomato flowers. MANOVA was conducted between factors and bee activity, followed by Pearson’s correlation. A Mann-Whitney U test was calculated to determine the significance between tomato flower bruising levels and fruit weights, followed by Cliff’s delta (d). Pollination activity decreased mainly in December and January when solar irradiation decreased to below 110 J cm⁻² day⁻¹. Bumblebee activity was significantly affected by solar irradiation with HPS lighting (p<0.001; p<0.01). There was a significant correlation between bumblebee activity and solar irradiation (r= 0.75; p<0.05), and solar irradiation with HPS lighting (r= 0.70; p<0.05). There was no correlation between bumblebee activity and fruit weights (r= −0.20; p<0.05). Bruised flowers had significantly greater fruit weight increases (165.7 g) compared to unbruised flowers (123.4 g) (d= 0.12; p<0.05). Bee activity rates between 60% to 80% can be concluded as an effective rate for tomato growers. Bumblebees need at least 110–154 J cm⁻² day⁻¹ of solar irradiation to achieve a high pollination activity rate in temperate climate zones during the winter season.