Relation between Dopa Decarboxylase activity and paralytic activity in Tenebrio molitor and Neobellieria bullata

Paralysins are endogenous compounds in immature insects that cause paralysis or death in adult individuals after injection into the thorax. We have proven the universal effect of paralysins by injection of paralysins from Neobellieria bullata into adult Tenebrio molitor and vice versa. The toxic effect of the tested, 30\% acetonitrile fraction from whole body homogenates depends on the stage of the insect from which the extraction was made. The activity of the paralysins shows a temporal distribution with the highest level at pupation and a second, smaller effect at eclosion. The dopa decarboxylase (DDC) activity, measured by using a radioactive labeled substrate, in developing N. bullata and T. molitor, peaks at the most important moments in the development of the insect: at pupation but especially at eclosion. The DDC enzyme could play an important role in the toxicity of paralysins. Relating the temporal distribution of toxic activity in both species to their correlated distribution of DDC activity shows the same pattern: DDC activity increases after stages that show high paralytic activity. Injection of beta-alanine-L-tyrosine (BAY, a known paralysin of Neobellieria bullata) into the thorax of adult flies did not induce the DDC activity. So, this could be the key to the toxic effect of BAY, because injection of BAY into the thorax of juvenile (pupae) Tenebrio molitor did cause an induction of DDC activity.