Elevation of dopamine levels in parasitized insect larvae

Abstract Last instar larvae of the armyworm, Pseudaletia separata , parasitized with the parasitoid wasp, Cotesia kariyai , suffer from retarded growth and do not initiate metamorphosis. Dopamine levels in hemolymph and nerve cord of host last instar larvae were increased by parasitization with parasitoid wasps. The elevation of dopamine levels was reproduced by injection with polydnavirus or growth-blocking peptide (GBP). Injection of dopamine or the dopamine agonist, (-)-Quinpirole, disturbs normal development of the armyworm larvae. These results suggest that GBP elevated by polydnavirus infection causes an increase of dopamine in hemolymph and nervous system, which is closely related to a disturbance of normal larval development.