Juvenile hormone synthesis in relation to corpus allatum development in embryos of the viviparous cockroach Diploptera punctata

Abstract

Summary Few studies have addressed endocrinology of the corpora allata (CA) in insect embryos. We now report on development and biosynthetic activity of CA in embryos of a viviparous cockroach, Diploptera punctata. When newly-eclosed adult females of D. punctata were mated, they oviposited and gave birth, respectively, about 8 and 73 days later; thus, gestation and corresponding embryogenesis lasted approximately 65 days. Dorsal closure, which coincides with differentiation of the CA, was concluded when embryos were about 13 days old and had completed 20% of embryogenesis. Reverse phase-high performance liquid chromatography revealed that embryonic CA released predominantly juvenile hormone III (JH) in vitro. Furthermore, an in vitro radiochemical assay showed that between day 28 of embryogenesis (43% of embryonic development completed) and hatch rates of JH synthesis rose, plateaued and then fell. When CA activity was increasing or was high, from day 28 to 54 (83% development), mitosis occurred at low and constant rates within embryonic CA, and corpus allatum cell number increased gradually. Between days 56 (86% development) and 60 (92% development), CA activity fell to a low level, rates of mitosis peaked, and corpus allatum cell number rose rapidly. Throughout embryogenesis, CA volume increased in parallel with CA cell number, suggesting that glandular growth was due largely to cell proliferation. Although CA activity and volume changed considerably in embryos, the diameter of corpus allatum cells, as measured from enzymatically dissociated CA, remained surprisingly constant at 11–12 μm on days 32, 46 and 60 (49, 71 and 92% development). Ultrastructural observations confirmed the large size of cells in low-activity CA of 60-day-old embryos and also showed that these cells, like those in highly active CA of 46-day-old embryos, contained abundant cytoplasm, ribosomes, microtubules and mitochondria.