Living With Zombie Cockroaches II

Jewel Wasp Stings a Cockroach
Photo: Ram Gal, J Experimental Biology

In a previous post, I discussed Zombie Cockroaches and the modulation of their behavior by parasitic wasps. The wasps inject a venom into the cockroach brain that contains dopamine or dopamine agonists (mimics). The dopamine causes behavioral changes in the cockroach, some of which benefit the wasp and some that do not. For example, stung cockroaches display a remarkable increase in antenna grooming. This behavioral change does not appear to affect success of the parasite and may be due to changes in the dopamine signaling pathway. The sting also affects the octopamine signaling system in the insect. The changes in octopamine signaling alter the cockroach motivation and lead to zombie-like changes in locomotion.

How could parasitoid wasps evolve “mind altering (cockroach mind)” venom? The wasp uses the same neurotransmitters, dopamine and octopamine as the cockroach and must control these systems in its own nervous system. Thus, the venom components were already present. A wasp ancestor that “added” dopamine or octopamine, their agonists or antagonists to its venom could have had increased success in producing progeny, leading to refinements in the interaction.

Human physiologists now realize that human pathogens can produce mind altering substances or cause changes to brain chemistry that lead to behavioral changes and “mental illness”. Recognized and treatment of patients to eliminate the pathogens has in some cases cured the “mental illness”. Study of parasite-host interactions in humans has limitation that require the use of model systems, and insects have emerged as important model systems. What we learn about insects may translate or inspire advances in human medicine.