Cuticle tanning, insects

The presence of catechols and more complex, oxidizable polyphenols in nature is widespread, and their functions are not limited to chemical defense. However, biological control of their oxidation is usually a feature of their function, as it is (1) in melanin synthesis,3 (2) in immunologically mediated delayed-type hypersensitivity responses,4 (3) in the hardening or curing of arthropod secretions (for example, as in the surface attachment adhesives of the barnacle and in tanning of the cuticle in insects),5 as well as (4) in defensive mechanisms in higher plants, particularly in the unleashing of immediate necrotrophic responses.6... 

During the past few years, a number of peptides have been isolated from insects and plants with very powerful hormonal or toxic effects (18, 19). Chapter 7 in this volume describes work on the effects of enzymes on cuticle tanning that are hormonal like in actions and have activity at low concentrations. 

Cutlcular permeability In Insects Is correlated with a number of factors Including growth stage of the Insect, surface to volume ratios, the degree of tanning In the cuticle, conditioning temperatures, and cutlcular lipids 2 ). The cuticle of... 

Cleavage of 3-hydroxykynurenine by kynureninase (step g, Fig. 25-11) forms 3-hydroxyanthranilate, which is opened under the action of another dioxygenase (step h) with eventual degradation to acetyl-CoA, as indicated. In insects the reactive 3-hydroxyanthranilate is utilized in "tanning" reactions, e.g., coupling to tyrosine residues to toughen insect cuticles and walls of cocoons.214... 

If the compound is causing the insect to be stressed or intoxicated, the insect larva (in this case a prepupa) may have trouble casting the old cuticle, yet be capable of tanning. Thus, the insect becomes a tanned larva or what appears to be a half pupa/half larva (due, in part, to incomplete ecdysis). For example, larvae treated with paraoxon (200 nmol./larva data not included in Table I due to high mortality) caused the formation of tanned larvae in all larvae treated. However, all of these larvae had obviously been adversely affected (intoxicated) by the paraoxon... 

Furthermore, many insects, particularly the adults, are protected against the entry of contact insecticides by thick and sclerotized cuticle (Ebeling, 1974). For example, newly molted American cockroach adults picked up three to four times more malathion than those that were darkly tanned (Matsumura, 1959). 

SO Anderson. Sclerotization and tanning of the cuticle. In Comprehensive Insect Physiology, Biochemistry and Pharmacology, Vol. 3. GA Kerkut, LI Gilbert, eds. New York Pergammon Press Ltd., 1985, pp. 59-74. 

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