Insects cuticle

Matsumura, F., The Permeability of Insect Cuticle, M.S. Thesis, University of Alberta, Edmonton, 1959. Olson, W.P. and O Brien, R.D., The relation between physical properties and penetration of solutes into the cockroach cuticle. /. Insect Physiol., 9, 777,1963. 

The chitinases present in the insects have been described from Bombyx mori and Manduca sexta. These enzymes play important roles as degradative enzymes during ecdysis, where endochitinases break randomly the cuticle to chitooligosaccharides that afterwards are hydrolyzed by exoenzymes to GlcNAc. The monomer is reused to s mthesize a new cuticle. Insect chitinases also have a defensive role against their own parasites. The production of enzymes in insects is regulated by hormones during the transformation of the larvae (Kramer and Muthukrishnan, 1997 Arakane and Muthukrishnan, 2010). 

Mode of Action. DDT and its analogues specifically affect the peripheral sense organs of insects and produce violent trains of afferent impulses that result in hyperactivity, convulsions, and paralysis. Death results from metaboHc exhaustion and the production of an endogenous neurotoxin. The very high lipophilic nature of these compounds faciUtates absorption through the insect cuticle and penetration to the nerve tissue. The specific site of action is thought to be the sodium channels of the axon, through inhibition of Ca " ATPase. 

Hurst (19) discusses the similarity in action of the pyrethrins and of DDT as indicated by a dispersant action on the lipids of insect cuticle and internal tissue. He has developed an elaborate theory of contact insecticidal action but provides no experimental data. Hurst believes that the susceptibility to insecticides depends partially on the cuticular permeability, but more fundamentally on the effects on internal tissue receptors which control oxidative metabolism or oxidative enzyme systems. The access of pyrethrins to insects, for example, is facilitated by adsorption and storage in the lipophilic layers of the epicuticle. The epicuticle is to be regarded as a lipoprotein mosaic consisting of alternating patches of lipid and protein receptors which are sites of oxidase activity. Such a condition exists in both the hydrophilic type of cuticle found in larvae of Calliphora and Phormia and in the waxy cuticle of Tenebrio larvae. Hurst explains pyrethrinization as a preliminary narcosis or knockdown phase in which oxidase action is blocked by adsorption of the insecticide on the lipoprotein tissue components, followed by death when further dispersant action of the insecticide results in an irreversible increase in the phenoloxidase activity as a result of the displacement of protective lipids. This increase in phenoloxidase activity is accompanied by the accumulation of toxic quinoid metabolites in the blood and tissues—for example, O-quinones which would block substrate access to normal enzyme systems. The varying degrees of susceptibility shown by different insect species to an insecticide may be explainable not only in terms of differences in cuticle make-up but also as internal factors associated with the stability of oxidase systems. 

Gosline, J.M., Lillie, M., Carrington, E., Gerette, P., Ortleppa, C., and Savage, K., Elastic proteins Biological roles and mechanical properties, Philos. Trans. R. Soc. Land. B Biol. Set, 357, 121-132, 2002. Weis-Fogh, T., A rubber like protein in insect cuticle, J. Exp. Biol., 37, 887-907, 1960. 

Electron microscopy and X-ray diffraction experiments conducted on resilin-containing insect cuticle provided further support for resilin existing in the rubbery state as a crosslinked random network of protein chains. No fine structure was revealed by the electron microscopy experiments and zero crystallinity could be detected from the X-ray diffraction experiments. Furthermore, the diffraction... 

Ohnishi, E. 1959. Pigment composition in the pupal cuticles of two colour types of the swallowtails, Papilio xuthus L. and P. pmtenor demetrius Cramer. J. Insect Physiol., 3 132-145. 

Christiansen, M.E. and J.D. Costlow, Jr. 1982. Ultrastructural study of the exoskeleton of the estuarine crab Rithropanopeus harrisii effect of the insect growth regulator dimilin (diflubenzuron) on the formation of the larval cuticle. Mar. Biol. 66 217-226. 

Christiansen, M.E., E. Gosling, and M.A. Williams. 1984. Effect of the insect growth regulator diflubenzuron (dimilin) on the uptake of glucose and V-acetylglucosamine into the cuticle of crab larvae. Mar. Biol. 83 225-230. 

Bedding RA, Molyneux AS. Penetration of insect cuticle by infective juveniles of Heterorhabditis spp. (Heterorhabditidae Nematoda). Nematol. 1982 28 354-359. 

The nematodes are themselves insect parasitoids that are not very particular about their hosts. Fly maggots, moth larvae and pupae, beetle larvae, and numerous other hosts are all acceptable to them. Some of these nematodes do have narrow preferences, but one widespread species invades more than two hundred different kinds of insects. Juvenile nematodes infected with their bacteria seek out a host to parasitize, typically gaining entry through one of its body orifices. Some species enter through a hole they scrape in the insect s cuticle using a "tooth" on their head. Once inside the insect, the worms force their way through soft tissues and into their host s central body cavity. 

A problem in trying to use these results in developing potential pest control agents is that none of these compounds is likely to penetrate either the cuticle or the CNS of insects effectively, since all are fully ionized at physiological pH. Derivatization of the polar groups would be one possible solution to this problem. The formamidines and imidazolines generally do not suffer from this problem since they have pKas which are lower than those of the related phenylethylamines and thus are at least partly in the free base form at pH 7. 

Penetration into insects is greatly influenced by the manner in which the compound is presented. Classic studies by Treherne (19) indicated that when the toxicant is supplied to detached insect cuticle in aqueous solution penetration decreased with increasing polarity, explicable on the assumption that partition into and passage through the lipoidal epicuticle is the rate determining step. In contrast several studies (20 - 22) have shown that when the toxicant is dissolved... 

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