Modulatory influence of juvenile hormone analogue (JHa) and 20-hydroxyecdysone on lipophorin synthesis in red cotton bug, Dysdercus cingulatus Fabr.

Topical supply of methoprene, a juvenile hormone analogue (JHa) caused notable morphological disturbance in insects. Topical supply of methoprene to newly emerged adult female D. cingulatus caused notable disturbance and induced a dramatic reduction in the total haemolymph protein pattern and lipophorin production in tissues like fat body, ovary and haemolymph. Total protein concentration in haemolymph also showed significant reduction in 1 day old insects but increased slightly as age advanced. Application of 20-hydroxyecdysone (20-HE) to 2-day-old adult female stimulated protein synthesis intensively. Lipophorin levels in fat body and ovary also simultaneously increased. Densitometric analysis revealed that methoprene inhibits while 20-HE stimulates lipophorin production in D. cingulatus.

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

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