Is larva metamorphosis controlled by positive feedback?

So when PTTH, a polypeptide neurohormone is released it stimulates a second hormone, ecdysteriod to be released. As long as JH is high, ecdysteriod stimulates molting, and when JH is low ecdysteriod induces formation of a pupa, within which metamorphosis occurs. Does this involve both positive and negative feedback or just positive feedback?