The effects of caffeine on the motor function of the honey bee, Apis mellifera

Caffeine is a bitter compound produced by plants to provide protection against herbivores and pathogens. Interestingly, low levels of caffeine have been detected in floral nectar, which contradicts nectar's role to attract pollinators. Previous studies have shown that caffeine increases alertness and activity levels in mammals and invertebrates, thus an increase in activity may enhance pollinator productivity and benefit plants. We examined the impact of caffeine on the motor function of the honey bee, Apis mellifera. Forager bees were collected from the colony entrance and fed 1 M sucrose to satiation. The following day, bees were fed 10 µl of 1.0 M sucrose or sucrose plus 10^-6 to 10^-3 M caffeine, which reflects concentrations naturally present in nectar. To determine if caffeine increases activity, subjects were transferred into an activity monitor that measured beam break counts for 1 hour using the DAMSystem360. One hour observations showed higher levels of activity among bees given 10^-5 and 10^-4 M caffeine concentrations. Also, these concentrations appear to prolong increased activity when the data is separated into 30 minute intervals.To examine the effects on specific behaviors, individual bees were transferred to a petri dish either 5, 30, or 60 minutes after caffeine consumption and were observed for 10 minutes. The amount of time bees spent performing mutually exclusive behaviors (Eg. walking, flying, fanning, stopped, and grooming) was recorded using The Observer 5.0. Caffeinated bees showed an increase in fanning and flying and a decrease in grooming.