Role of dopamine at the onset of pupal diapause in the cabbage armyworm Mamestra brassicae.

Experiments were conducted to examine the relationship between an onset of diapause and dopamine (DA) content in the cabbage armyworm Mamestra brassicae during pupation. The DA levels were significantly higher in haemolymph, integument and brain-central nervous system of diapause-destined pupae than in non-diapause-destined pupae. The elevated level of the integumental DA content was demonstrated to be due to an increase in dopa decarboxylase activity in diapausing pupal integuments through an enhancement of transcript levels of this enzyme. Elevation of the DA level accomplished by feeding L-DOPA to last instar larvae induced a diapause-like state in more than 50% of the pupae under long daylengths.