Diploptera punctata as a model for studying the endocrinology of arthropod reproduction and development

The Pacific beetle cockroach, Diploptera punctata, has proven to be a valuable model insect in the study of the dynamics regulating juvenile hormone (JH) biosynthesis and metabolism, particularly during late nymphal development and reproduction. This stems in part from its unusual mode of reproduction, adenotrophic viviparity, in which females give birth to live young that have been nourished throughout embryonic development by a protein-rich 'milk' secreted by the wall of the brood sac or uterus. In this animal, as in most insects, JH regulates both vitellogenin production and its uptake by developing oocytes. However, JH has an antagonistic effect on embryonic development and following oviposition of the fertilized oocytes into the brood sac, JH production halts, in part through the action of a peptide family, the FGLa allatostatins. JH production remains at a low level throughout pregnancy and is only reinstated at the end of gestation, at which time, the next wave of oocytes begins to develop and enter vitellogenesis. Thus, JH production in this species is precisely regulated, since the appearance of JH at inappropriate times would result in abortion of the embryos. Numerous factors are responsible for the regulation of JH biosynthesis, including peptides, biogenic amines, neurotransmitters, ecdysteroids and second messenger effectors. In this review, we discuss these factors and highlight potentially fruitful areas of future research. Although several of the enzymes of the biosynthetic pathway have been cloned, the precise points of rate limitation remain uncertain. The dissection of the biosynthetic pathway and its control awaits the completion of the genome and transcriptome of this important model insect.