The Role of Juvenile Hormone Metabolism in the Metamorphosis of Selected Lepidoptera

Abstract

In this chapter we will present an evaluation of the role of juvenile hormone (JH) catabolism in the Lepidoptera. This will be accomplished by first describing observations on the regulation of the esterase activity which hydrolyzes JH (JH esterase) during the last larval stadium, then describing the synthesis and kinetics of selective inhibitors of JH esterase, and finally describing the use of these inhibitors as probes for elucidating the biological role of JH esterase in the metamorphosis of selected Lepidoptera. Support for three hypotheses will be advanced. First, that in the Lepidoptera examined, JH ester hydrolysis is a major route of JH catabolism and that in the cabbage looper (Noctuidae, Trichoplusia ni) and in the tobacco horn worm (Sphingidae, Manduca sexta) this hydrolysis is due largely to a single enzyme at developmentally critical times. Second, this single protein in the early last larval stadium possibly is under the control of neurosecretory factors, while in the prepupal period JH directly results in JH esterase production. Finally, we advance the concept that in contrast to reports in vertebrates, where hormone titer is regulated by constant degradation and variations in biosynthesis, that titer of JH is, in part, controlled by a reduction in rate of biosynthesis and a large increase in the levels of catabolic enzymes.