Insect prothoracic glands: function and ultrastructure in diapause and non-diapause larvae of Diatraea grandiosella

Abstract

The function and fine structure of the larval prothoracic glands (PG's) of the southwestern corn borer, Diatraea grandiosella Dyar, were examined. A novel vacuum-ligation technique was developed to isolate whole PG's from the hemocoel of last-stage non-diapause larvae. This treatment prevented larvae from pupating unless they received an injection of β-ecdysone and thereby confirmed the need for a hormonal secretion from the PG to initiate molting.The structure of PG's from mature non-diapause and diapause larvae was compared. Each gland consists of about 33 large secretory cells, and receives efferent neurones, some of which are neurosecretory, from the central nervous system. Each PG cell of a non-diapause larva is bounded by a thin tunica propria and consists of a large nucleus and a dense cytoplasm containing evenly dispersed mitochondria, ribosomes, and glycogen particles. In contrast, each inactive PG cell of a diapause larva is bounded by a thick tunica propria and contains a shrunken convoluted nucleus and an inner cytoplasmic zone of glycogen particles.