Pergamon J. Insect Physiol. zyxwvutsrqponmlkjihgfedcbaZYXWVU Vol. 42, No. 7, 705-709, 1996 pp. Copyright 0 1996 Elsevier Science Ltd PII: SOO22-1910(96)00006-6 Printed in Great Britain. All rights reserved 0022-1910196 $15.00 + 0.00 Water Loss During Cuticle Sclerotization in the Medfly Ceratitis capitata is Independent of Catecholamines PABLO WAPPNER,* LUIS A. QUESADA-ALL&*? Received 8 June 1995; revised and accepted 31 October 1995 Insect cuticles undergo a striking water loss during the process of sclerotization. It has been considered that such dehydration is due to a physico-chemical displacement of the water due to incorporation of catecholamines. The dehydration of the puparium in the Medfly Cerutitis capituta throughout pupariation was studied. Water loss in the white pupa mutant, that fails to export catecholamines to the puparium, was not significantly different from that of the wild type or a melanic mutant strain, both with high content of cuticular catecholamines. These results are in clear contradiction to the catecholamine-displacement model for cuticle dehydration. An alternative model explaining the mechanism of water loss during sclerotiz- ation is proposed. Copyright 0 1996 Elsevier Science Ltd Ceratitis capitata Cuticle dehydration Puparium Pupariation Dipteran metamorphosis INTRODUCTION Insect cuticle sclerotization involves proteins and chitin covalent cross-linking mediated by oxidation products of catecholamines (Pryor, 1940b; Andersen, 1985; Schaefer et al., 1987; Hopkins and Kramer, 1992; Ricketts and Sugumaran, 1994). It is well known that sclerotization is always accompanied by a dramatic cuticular water loss (Fraenkel and Rudall, 1940). It has been proposed that such cuticle dehydration is due to the incorporation of catecholamines that, because of an increase in hydro- phobicity, would produce a physico-chemical displace- ment of the water (Pryor 1940a,b; Vincent and Hillerton, 1979; Brunet, 1980; Hackman, 1984; Andersen, 1985; Schaefer et al., 1987; Hopkins and Kramer, 1992). Therefore, sclerotization and displacement of water out from the cuticle would depend on the epidermal export of catecholamines. Nevertheless, no direct evidence sup- ports such a theory. As Brunet ( 1980) pointed out, it remains to be determ- ined whether water is displaced out of the cuticle by the incorporation of catecholamines or if, alternatively, an external system such as an epidermal ‘pump’ brings *Institute de Investigaciones Bioquimicas ‘Fundacibn Campomar’ and University of Buenos Aires, A. Machado 151, Buenos Aires, (1405), Argentina. l-To whom correspondence should be addressed. about cuticle dehydration. To our knowledge, after Bru- net’s formulation, this question was not investigated further, though the former possibility was favored in the literature We have recently characterized the white pupa mutant of the Medfly Ceratitis capitata, as a strain with a cat- echolamine incorporation impairment, a strain that lacks o-diphenol tanning of the puparium (Wappner et al., 1995). Taking advantage of this mutant, we were able to study the water loss qf an insect cuticle in a catechol- amine-free situation, thus dissecting dehydration and tan- ning events and thereby addressing Brunet’s open ques- tion. MATERIALS AND METHODS Insects Ceratitis capitata larvae were reared as described in Quesada-All& et al. (1994) or generously provided by Fanny Manso from the Instituto de GenCtica, INTA, Cas- telar. Wild type ARG-17 (Rabossi er al., 1991), niger (Manso and Lifschitz, 1979) and white pupa (Rossler, 1979) strains were obtained from the Castelar collection. The adults were fed a mixture of yeast and sugar. The insect growth chamber was maintained at 23”C, 55-80% relative humidity and subjected to a light/dark regime of L16:D8 h. 705