Prior Experience with Food Reward Influences the Behavioral Responses of the Honeybee Apis mellifera and the Bumblebee Bombus lantschouensis to Tomato Floral Scent

Pupal and Adult Experience Affect Adult Response to Food Odour Components in the Flower-Visiting Butterfly Tirumala limniace

Butterflies have the ability to learn to associate olfactory information with abundant food sources during foraging. How the co-occurrence of both food and food odours affects the learning behaviour of adults and whether butterflies perceive the odour of their surroundings and develop a preference for that odour during the pupal stage have rarely been tested. We examined the effect of experience with food odour components (α-pinene and ethyl acetate) during the pupal and adult stages on the foraging behaviour of the flower-visiting butterfly Tirumala limniace. We found that α-pinene exposure during the pupal stage changed the foraging preference of newly emerged adults. T. limniace exhibits olfactory learning in the adult stage, and adult learning may influence their previous pupal memory. Moreover, adults' odour preference did not continue to increase over multiple training times. The learning ability of adults for floral odours (α-pinene) was greater than that for non-floral odours (ethyl acetate). In contrast to previous studies, we found that males learned odours more efficiently than females did. This could be attributed to differences in antennal sensilla, affecting sensitivity to compounds and nectar demand between males and females. Our study provides further insight into how olfactory learning helps flower-visiting butterflies use food odours to forage better.

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

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.

Odor-Pollution From Fungicides Disrupts Learning and Recognition of a Common Floral Scent in Bumblebees (Bombus impatiens)

Background and Aims

Bumblebees provide vital pollination services to both natural and agricultural ecosystems. Consequently their declines in species-diversity and population size over the last five decades is alarming. Direct contributors to these declines include pesticides, habitat loss, and disease. However, given that colony fitness is linked to foraging success, successful conservation requires mitigation of any anthropogenic practices that negatively impact foraging. Previous work has shown that agrochemical odor-pollution, including that of fungicides, can modulate bumblebee foraging behavior. This study investigates how odor pollution from three common fungicides (Safer® Brand Garden Fungicide II, Scotts® Lawn Fungus Control, and Reliant® Systemic Fungicide) affects Bombus impatiens’ floral-odor learning and recognition using an associative learning paradigm.

Methods

The effects of fungicide-odor pollution were tested in three ways: (1) background pollution during floral-odor learning; (2) background pollution during floral-odor recognition; and (3) point (localized) pollution during floral-odor recognition. Electroantennogram (EAG) recordings from B. impatiens confirmed the salience of all odor-stimuli and examined impacts of background fungicide-odor on antennal responses to floral-odor. To better understand how fungicide-odor structure related to behavioral data, scents were sampled (Solid Phase Microextraction) and analyzed using gas chromatography–mass spectrometry. Odors were then characterized using the Compounds Without Borders (CWB) vectorization method.

Conclusion

All fungicides tested disrupted floral-odor learning and recognition for at least one concentration tested, and Scotts® was universally disruptive at all tested concentrations. All fungicides induced EAG responses, indicating they provide perceivable odor stimuli. Interestingly, two of three tested fungicides (Scotts® and Reliant®) inhibit antennal responses to Monarda fistulosa odor. Odor characterization supports previous findings that sulfurous scents could be disruptive to odor-driven foraging behaviors. Inability for foraging bumblebees to associate to rewarding floral odors in the presence of fungicidal odor pollution could have negative large-scale implications for colony health and reproductive fitness.