Effects of Octopamine on Aggressive Behavior in Red Wood Ants

Octopamine plays a key role in regulating aggression in solitary insects, though data on its role in mediating aggression in social insects are contradictory. In insect families, the queen can influence brain octopamine contents and aggressivity in worker individuals. We report here our studies on the effects of octopamine and the presence of a queen on aggressive behavior in Formica aquilonia ants when confronting their natural predators, i.e., ground beetles. Feeding with octopamine increased the frequency of attacks on and pursuits of beetles by ants and decreased the frequency of nonaggressive reactions. Injection of epinastine (an octopamine receptor antagonist), as compared with octopamine, led to an increase in the frequency of avoidance reactions and a decrease in the number of pursuits. Contrary to expectation, the presence of a queen in the group had no effect on aggression in workers. Feeding with octopamine-containing syrup for two weeks had no effect on the rate of movement of the ants. This points to a movement-independent modulatory action for octopamine on aggressive behavior in ants. It is suggested that in red wood ants, octopamine may be involved in regulating the separation of functions in the family, based on the link between aggressivity and the specialization of worker individuals.

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