Physiological mechanisms of insect density-dependent phase polymorphism: Lepidoptera
A detailed review of the literature on the physiological mechanisms of control of the density-dependent phase polymorphism (PP) in the Lepidoptera has been carried out Analysis of the literature on insect phase polymorphism shows the leading role of the neuroendocrine system in the regulation of this phenomenol. Density of population is the main signaling factor affecting activity of the neuroendocrme organs and, therefore, determines level of major hormones in the hemolymph of Lepidoptera and other insects One of the main hormones controlling these processes is the juvenile hormone (JH) An important feature of insect endocnne control is polyfunctionahty of the mam hormones Thus, JH takes part in the regulation of several vital processes morphogenesis, development of the reproduction system, direction and mtensity of the metabolism In the Lepidoptera with the pronymphal facultative diapause, a high JH titre blocks the pupal moult and ensures the resting state Ecdysteroids control the processes of moulting and metamorphosis, as well as participating in cell differentiation processes Peptide neurohormones released by the neurosecretory cells of the brain and vanous ganglia regulate many vital processes and can be secreted as a response to various signalling factors, including population density The dynamics of the hormonal balance is of great importance in insect ontogenesis, particularly in respect of the balance of JH and ecdysteroids which can change considerably accordmg to population density, as shown for several species with phase polymorphism Hence when studymg physiological effects of Lepidoptera population density, it is necessary to test the hormonal status of individuals (primarily the JH and ecdysteroid systems) It is also highly desirable to monitor a broad set of morphoecological parameters, such as caterpillar coloration (the degree of the cuticle melamzation), the duration of vanous developmental stages, and weight of caterpillars (especially at the end of development) and pupae, as well as imago fertility, since many of these are subject to hormonal control