Octopamine influences honey bee foraging preference

Abstract

Colony condition and differences in individual preferences influence forage type collected by bees. Physiological bases for the changing preferences of individual foragers are just beginning to be examined. Recently, for honey bees octopamine is shown to influence age at onset of foraging and probability of dance for rewards. However, octopamine has not been causally linked with foraging preference in the field. We tested the hypothesis that changes in octopamine may alter forage type (preference hypothesis). We treated identified foragers orally with octopamine or its immediate precursor, tyramine, or sucrose syrup (control). Octopamine-treated foragers switched type of material collected; control bees did not. Tyramine group results were not different from the control group. In addition, sugar concentrations of nectar collected by foragers after octopamine treatment were lower than before treatment, indicating change in preference. In contrast, before and after nectar concentrations for bees in the control group were similar. These results, taken together, support the preference hypothesis.

Figure 1

Proportion of identified nectar foragers returning to the colony with nectar or water after octopamine (1mg/ml octopamine in 50% w/v sucrose solution) or control (50% w/v sucrose solution) treatment in each colony. P values refer to non-parametric statistics comparing frequencies of nectar and water foragers in each treatment group for each colony.

Figure 2

Comparison of sugar concentration in nectar collected before and after treatment (Colony 3). Bees in the control group did not change their preference. A control bee that collected nectar with high or low sugar concentration before the experiment, did the same after the experiment. This lead to a significant positive correlation for sugar concentration of nectar collected by bees in the control group before and after the experiment. In contrast, the bees in the octopamine treatment group collected ‘nectar’ with lower sugar concentration after the experiment ( one-tailed paired t-test : t=1.85, df=17, P < 0.05). This lead to a lack of correlation for sugar concentration of nectar collected by bees in the octopamine treatment group before and after the experiment. N is 14 in the control group, and 18 in the octopamine group.

Figure 3

Nectar load collected by bees in control and octopamine treatment groups. In Colony 1, foragers in the octopamine treatment group collected greater nectar loads than bees in the control group ( t-test: t= 2.52, df=1, P < 0.03 ). In Colony 2 there were no significant differences across the groups (t-test: t=0.7, df = 1, P = 0.50). Bars indicate mean (±SE) forage load for groups. Asterisk refers to significant difference across the treatment and control group at 5% level. NS means the difference is statistically not significant.

Figure 4

Proportion of identified nectar foragers returning to the colony with nectar or water after octopamine (1mg/ml in 50% w/v sucrose solution), tyramine (1mg/ml in 50% w/v sucrose solution) or control (50% w/v sucrose solution) treatment. Letters above columns refer to non-parametric statistical analyses. Groups marked by different letters differ at the 5% significance level.