OCTOPAMINE, A MODULATOR OF THE HEMOCYTIC NODULATION RESPONSE OF NONIMMUNE GALLERIA-MELLONELLA LARVAE

Octopamine (1) injected into Galleria mellonella induced changes in the haemograms of the larvae identical to those in insects infected with Bacillus cereus, (2) was elevated during bacterial infection in vivo, and (3) accelerated the removal of microorganisms from the haemolymph. The modulation of these non-self responses by octopamine was independent of prophenoloxidase activation. Octopamine in vitro bound to the surface of the insect pathogens B. cereus and Xenorhabdus nematophilus. Injecting the octopamine-coated bacteria accelerated their removal from haemolymph over a 30 min post-injection period. It is proposed that octopamine is a bifunctional molecule acting as both a modulator of haemocyte activity and mediating bacterial attachment to haemocytes.