Possible regulation of feeding behavior in cockroach nymphs by the neurotransmitter octopamine

Insects, including cockroaches, have the ability to select a proper diet from different nutrient choices. We have showed previously that various neurotransmitters and neuromodulators appear to regulate certain aspects of feeding in the cockroach, Rhyparobia madera. In the current study, we examined the role of octopamine in feeding behavior of cockroach nymphs. By either injection or direct incorporation into the diet blocks, an octopamine agonist (octopamine or synephrine) or antagonist (phentolamine) was effective in altering feeding in R. madera nymphs. Both octopamine and synephrine increased feeding slightly, while phentolamine decreased feeding dramatically. Phentolamine was able to decrease feeding, but not motor activity, when injected directly into the nymphs. Octopamine appears to cause increased feeding in the cockroach.