Floral scent affects bumblebee pollinator preferences on the flowers of four tomato cultivars under greenhouse conditions

Bumblebee pollination is essential for greenhouse tomato. Floral traits, such as olfactory signal and food reward, have significant influences on pollinator foraging decisions and thus result in different pollination performance. Chemical-analytical, bioassays, and electroantennogram tests were used to determine whether these tomato Lycopersicum esculentum cultivars differed in floral scent and food reward, and how these floral traits affected bumblebee Bombus lantschouensi visitation performance. Bumblebees showed obvious foraging preferences among different tomato cultivars (P = 0.001). Compared with the other 3 cultivars, fewer bumblebees visited the 'Jingdanxiaohuangyu' cultivar. Moreover, the pollen quantity in the 'Jingdanxiaohuangyu' and 'Qianxi' cultivars (3.1×104-3.2×104) was lower than that in the 'Pingguoqing' and 'Zhefen' cultivars (8.5×104-8.6×104). In the floral scent composition analysis of the 4 cultivars, the floral components of 'Jingdanxiaohuangyu' were significantly different from those of the other 3 cultivars (P = 0.0032), and naïve bumblebees showed repulsion by the floral scent of 'Jingdanxiaohuangyu' (P = 0.035). Gas chromatographic-electroantennographic detection recordings and behavior choice tests revealed that the electroantennogram (EAG)-active compound isophorone, which only occurred in the floral scent of 'Jingdanxiaohuangyu', had a repellent effect on bumblebees. These findings suggest that olfactory signals from host flowers play an important role in regulating bee pollinator foraging behaviors, and more attention should be given to volatile-mediated pollinator attraction during tomato breeding.