Differences in EAG Response and Behavioral Choices between Honey Bee and Bumble Bee to Tomato Flower Volatiles

SIMPLE SUMMARY: Tomatoes are a popular crop, and bumble bees and honey bees are its main pollinators. Floral scent usually plays an important role in mediating the foraging behavior of bees, and tomato flowers release special scents. Although it has been found that foraging experience in the tomato greenhouses helped bumble bees develop a strong preference for the scent, honey bees with foraging experience continued to show aversion to tomato floral scent. However, it is currently unknown as to how a single tomato volatile compound regulates the foraging behavior of bees. In the current study, we investigated the foraging behaviors of the widely used pollinator honey bee Apis mellifera and bumble bee Bombus terrestris on tomato flower volatile compounds in order to evaluate whether honey bees and bumble bees show different EAG responses to volatile compounds and how they might influence bee choice behavior. We found that honey bees had a weaker EAG response to the tested compounds compared with bumble bees and that they showed avoidance behavior to these compounds. We conclude that some compounds in tomato floral scents caused the low bias of honey bees to tomato flowers, which may be one driver as to why honey bees dislike tomato, which could be adjusted in order to improve the pollination service efficiency of bees for commercial crops. ABSTRACT: Bumble bees and honey bees are of vital importance for tomato pollination, although honey bees are less attracted to tomato flowers than bumble bees. Little is known about how tomato flower volatile compounds influence the foraging behaviors of honey bees and bumble bees. In this study, compounds of tomato flower volatiles were detected by gas chromatography–mass spectrometry. Electroantennography (EAG) and a dynamic two-choice olfactometer were used, respectively, to compare the differences of antennal and behavioral responses between Apis mellifera and Bombus terrestris towards selected volatile compounds. A total of 46 compounds were detected from the tomato flower volatiles. Of the 16 compounds tested, A. mellifera showed strong antennal responses to 3 compounds (1-nonanal, (+)-dihydrocarvone, and toluene) when compared with a mineral oil control, and B. terrestris showed 7 pronounced EAG responses (1,3-xylene, (+)-dihydrocarvone, toluene, piperitone, eucarvone, 1-nonanal, and β-ocimene). Additionally, 1-nonanal and (+)-dihydrocarvone elicited significant avoidance behavior of A. mellifera, but not of B. terrestris. In conclusion, bumble bees are more sensitive to the compounds of tomato flower volatiles compared to honey bees, and honey bees showed aversion to some compounds of tomato flower volatiles. The findings indicated that compounds of flower volatiles significantly influenced bee foraging preference for tomato.