Abstract
A radiochemical assay (RCA) has been used for the measurement of juvenile hormone (JH) synthesis in vitro by corpora allata (CA) from the Eri silkworm, Samia cynthia ricini. Using CA from newly emerged female adults for the bioassay, the most suitable incubation conditions were determined. A high rate of JH synthesis was found in medium TC199 at pH 6.5, 30°C and 4 mM Ca2+. The time course of JH synthesis showed a steady decrease during the first 6 hours of incubation.Under optimal incubation conditions, CA from the 4th and 5th larval instars, pupae and adults were used for measuring JH synthesis in vitro. The highest rates of JH synthesis were found on the 1st day of both larval stages, and then JH synthesis decreased steadily during the following two days of each instar. From the 4th day of the 5th larval instar to the 2nd day after pupation, CA could still synthesize small amounts of JH. However, from the 3rd day of the pupal stage to 12 hours before adult emergence, no JH release was observed. About 6 hours before emergence, CA of both female and male pharate adults regained the ability to synthesize JH. JH synthesis increased to a maximum shortly after emergence and then decreased again during the following two days. During this period, JH synthesis in vitro by CA from females was always higher than that of males. This is the first report on JH synthesis in vitro by CA from both female and male pharate adults and adults of a lepidopteran species, where the adults do not feed, are relatively short-lived, mate only once, and ovarian maturation and vitellogenesis are completed before emergence.
Highlights
Juvenile hormone, a unique insect sesquiterpenoid hor mone, is produced by the corpora allata (CA)
juvenile hormone (JH) synthesis showed an optimum at pH 6.5, which corre sponds to the pH of S. cynthia ricini hemolymph
Medium TC199 was first chosen as an optimal medium for the desert locust Schistocerca gregaria (Tobe & Pratt, 1974), used for other insect species (Guan & Chen, 1986, Weaver et al, 1980), including Lepidoptera, M. sexta (Kramer & Law, 1980) and the corn earworm, Heliothis armigera (Guan et al, 1995)
Summary
A unique insect sesquiterpenoid hor mone, is produced by the corpora allata (CA). Metamorphosis to the pupa or adult form requires a reduced level or absence of JH (reviewed by Riddiford, 1994). JH regulates many reproductive functions, including vitellogenesis, sper matogenesis and growth of the accessory sex gland (ASG) (reviewed by Wyatt & Davey, 1996). The rate of JH synthesis appears to be regulated by stimulating and inhibiting neuropeptides, allatotropins (AT) and allatostatins (AST) (reviewed by Stay et al, 1994; Guan, 1996). Before studying AT and AST in an insect species, it is necessary to optimize the radiochemical assay (RCA) for the measurement of JH synthesis in vitro by corpora allata (CA) (reviewed by Feyereisen, 1985)
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