Insect juvenile hormone: from "status quo" to high society.

K Hartfelder

doi:10.1590/s0100-879x2000000200003

Abstract

Juvenile hormone (JH) exerts pleiotropic functions during insect life cycles. The regulation of JH biosynthesis by neuropeptides and biogenic amines, as well as the transport of JH by specific binding proteins is now well understood. In contrast, comprehending its mode of action on target organs is still hampered by the difficulties in isolating specific receptors. In concert with ecdysteroids, JH orchestrates molting and metamorphosis, and its modulatory function in molting processes has gained it the attribute "status quo" hormone. Whereas the metamorphic role of JH appears to have been widely conserved, its role in reproduction has been subject to many modifications. In many species, JH stimulates vitellogenin synthesis and uptake. In mosquitoes, however, this function has been transferred to ecdysteroids, and JH primes the ecdysteroid response of developing follicles. As reproduction includes a variety of specific behaviors, including migration and diapause, JH has come to function as a master regulator in insect reproduction. The peak of pleiotropy was definitely reached in insects exhibiting facultative polymorphisms. In wing-dimorphic crickets, differential activation of JH esterase determines wing length. The evolution of sociality in Isoptera and Hymenoptera has also extensively relied on JH. In primitively social wasps and bumble bees, JH integrates dominance position with reproductive status. In highly social insects, such as the honey bee, JH has lost its gonadotropic role and now regulates division of labor in the worker caste. Its metamorphic role has been extensively explored in the morphological differentiation of queens and workers, and in the generation of worker polymorphism, such as observed in ants.

Highlights

Few hormones have puzzled and fascinated entomologists more than juvenile hormone (JH)
The intention of this review is to present, as briefly as possible, the basic paradigms of this hormones function and physiology in insects, and to concentrate more on its wide-ranging ecological implications, i.e., to show how profoundly it can shape and even modify life histories
In the larval and pupal stages of insect life cycles, Juvenile hormone (JH) is known to modify the expression patterns of ecdysteroid-regulated genes, creating the possibility for an insect to express different types of cuticles, and in particular to develop from a larval form to an adult form through a complex metamorphosis

Summary

Introduction

Few hormones have puzzled and fascinated entomologists more than juvenile hormone (JH) This is obviously due to the hormones pleiotropic functions, from a) orchestrating metamorphosis in concert with the molt-inducing ecdysteroid hormones, b) regulating female fertility by stimulating vitellogenin synthesis in the fat body and its uptake by the growing oocytes, up to the c) generation of sophisticated polymorphisms in aphids and social insects. In this sense, JH is clearly a pleiotropic master hormone of insects which governs most aspects of their integration with the ecosystem and affects decisive life history parameters during their entire life cycles. We may come to a broader comprehension of how each class of animals has dealt during its evolution with such basic problems as homeostasis, as well as coordinated development and reproduction in variable environmental conditions

Objectives

Findings

Conclusion