Evaluation of electrophysiological responses of bumblebee pollinators to floral scents of oil pumpkin

Bumblebees are important pollinators of wild and crop plants, among them the Styrian oil pumpkin ( Cucurbita pepo subsp. pepo var. styriaca Greb.). The flowers of this economically important crop species release strong scents, dominated by 1,4-dimethoxybenzene, which are believed to be involved in the attraction of the bumblebees to the flowers. To determine the volatiles that elicit physiological responses in the antennae of Bombus terrestris , the most important bumblebee pollinator species of Styrian oil pumpkin in Europe, we performed gas chromatography-electroantennographic detection (GC-EAD) analyses using both natural floral scent samples and synthetic blends. The synthetic blend contained a mixture of 21 volatile compounds in similar amounts, independent of whether they have been dominant or minor compounds in the natural samples. From the measurements with natural samples, we found that only 1,4-dimethoxybenzene elicited strong responses, with few other compounds eliciting only weak responses. However, in the measurements with the synthetic blends, most of the 21 compounds including terpenoids and benzenoids/phenylpropanoids, showed similar responses as 1,4-dimethoxybenzene. This study demonstrates that the antennae of bumblebees respond to a high number of floral scent compounds of pumpkin, which all have the potential to attract pollinators and thus contribute to fruit set of this commercially important crop. The compounds identified as being EAD-active in the present study can be used in future studies to determine the effects of these compounds, as a mixture and as individual compounds, in attracting bumblebee pollinators to pumpkin flowers.