Insect metamorphosis

Very-long-chain methyl-branched alcohols (C38 to >C44) and their esters with short-chain acids (C2 to C5) represent a novel class of long-chain internal lipids which mainly occur during insect metamorphosis (Nelson, 1993). The very-long-chain methyl-branched alcohols were first characterized in the internal lipids of developing pupae (pharate adults)... 

At the outset, it appeared that proteinaceous products dispatched by a special class of neurosecretory neurons, such as those of the pars intercerebral is of insects, function exclusively in a neurohormonal capacity. Following the classical discovery by Kopec (1922) of a brain hormone controlling insect metamorphosis much information has been gained on a number of essential neurohormonal functions carried out by neuropeptides in the control of postembryonic development as well as reproductive, metabolic, muscular, and additional activities. 

Hormones have an important role in insect metamorphosis. In many species, two classes of hormones, moltirp hormones (made by the prothoracic glands) and juvenile hormones (made by the corpora allata) act together to control metamorphosis. Each regulates the expression of different genes, so that a charpe in their relative concentrations causes metamorphosis, the development of different body patterns. 

The potential for using endocrine imbalance as a means of insect pest control was suggested by Williams (9,10) He proposed that exposing immature insects to juvenile hormone (JH) at the time of metamorphosis, when JH is normally absent, would cause abnormal development and individuals incapable of survival. Since insect metamorphosis is unique, JH disruption would affect only insects. This would result in an environmentally safe approach to insect control as compared to current chemical pesticides which are less insect specific and more biocidal. The JH approach to pest insect control is most effective when adults are the destructive stage, and commercial preparations of JH mimics are available for use in the control of adult flies, mosquitoes, and fleas and, recently, for cockroach reproduction. However, many pest insects are destructive as larvae. 

Table 8 lists phytoecdysteroids alongwith other common steroids isolated from the yew. These consist of a number of closely related active compounds (insect metamorphosis hormones) possessing insect molting activity. The most common of these phytoecdysteroids is ecdysterone (271). 

Trifluoromethyl ketones (TFKs) have been found to inhibit various hydrolytic enzymes (1-6 ). Series of aliphatic and aromatic trifluoromethyl ketone sulfides (7-10 ) proved to be exceptionally powerful inhibitors of insect juvenile hormone esterase (JHE), an enzyme of key importance in insect metamorphosis. The trifluoroketone moiety is believed to behave as a transition state mimic (11,12) of juvenile hormones (JHs), substrates of the enzyme. The /3 sulfur atom is anticipated to mimic the a-/3 double bond present in all natural JH substrates. In earlier structure-activity relationship (SAR) studies (7,11) clear correlation was found among the molar I50 values of these compounds against JHE and the calculated molar refractivlty of the inhibitors. 

Enseal yourself into and fly out of the cocoon. The three stages of insect metamorphosis are pro-nymph, nymph and adult within the cocoon larva, pupa and adult [1415]. The cocoon shell of the silk worm Bombyx mori is soaked with antibacterial proteins [1416]. During metamorphosis, apoptosis and autophagy... 

Volume 28. Morphogenesis, differentiation and development I. Fertilization by A. Monroy. II. Behaviour of nucleic acids during early development by J. Brachet. 111. Biochemical pathways in embryos by E. Scarano and G. Augusti-Tocco. IV. Factors of embryonic induction by T. Yamada. V. Biochemistry of amphibian metamorphosis by R. Weber. VI. Biochemical correlations in insect metamorphosis by L. I. Gilbert. Subject index. 

V. B. WiGGLESwoRTH, The Physiology of Insect Metamorphosis, Cambridge Monographs in Exptl. Biol., i. University Press, London, 1954. 

P. Karlson and C. E. Sekeris, Biochemistry of Insect Metamorphosis, in M. Florkin AND H. Mason, Comparative Biochemistry, Vol. V, Academic Press, New York, in the press. 

Two hormones known to regulate insect metamorphosis and development are the juvenile hormones and 20-hydroxyecdysone. Juvenile hormone inhibits progress toward the adult form and 20-hydroxyecdysone is the driving force for molting. For 20 years juvenile hormone agonists have been the subject of intensive chemical research providing several new insecticides, including methoprene and kinoprene (2). 

Oxacyclopropane (oxirane, ethylene oxide) is a large-volume industrial chemical intermediate and a fumigating agent for seeds and grains. In nature, oxacyclopropane derivatives control insect metamorphosis (see Real Life 12-1) and are formed in the course of... 

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