Corpora allata (CA) from adult egg-carrying Indian stick insects, Carausius
morosus, synthesise and release juvenile hormone (JH) III in vitro. No JH
biosynthesis was observed in larvae, young adults, and old adult females th
at do not carry sclerotised eggs. In females, which bear sclerotised eggs,
a consistent JH biosynthesis was observed. Supplementation of precursors of
JH biosynthesis (farnesol, mevalonic acid lactone) greatly enhanced JH bio
synthesis in a stage-, age-, and dose-dependent manner, but CA from the las
t larval instar retained the biosynthesised JH within the gland. Elevated c
alcium concentration in the incubation medium stimulated JH biosynthesis by
CA from older adults but had either no or a poor effect on CA from young a
dults and larvae. The results obtained with farnesol, mevalonic acid lacton
e, and calcium indicate that the rate-limiting steps of JH biosynthesis ver
y Likely occur before the formation of mevalonic acid and that these early
steps cannot be stimulated by elevated calcium concentrations in larvae and
young adults. In older adults, in which spontaneous JH biosynthesis occurs
, elevated calcium concentration can markedly stimulate JH biosynthesis. A
pre-purified extract from brains of adult females had a stimulating effect
on JH biosynthesis by CA from adult females. The results indicate that JH b
iosynthesis in C. morosus may require food-derived farnesol and may be regu
lated by allatotropic signals from the brain, possibly triggered by sclerot
ised oocytes in the ovary. (C) 1999 Elsevier Science Ltd. All rights reserv
ed.