Octopaminergic system orchestrates combat and mating behaviors: A potential regulator of alternative male mating tactics in an armed beetle

•-Neurochemical basis of fighting behavior was examined in a weaponed beetle.•-Oral administration of octopamine agonists suppressed male-male aggression.•-Octopaminergic system increased sperm size and dispersal activity.•-Octopamine was suggested to regulate non-fighting alternative mating tactic.