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Larvae of the 5th‐instar tobacco hornworm, Manduca sexta(L.), were fed artificial diets containing either 2.5 mM canavanine or 2.5 mM canavanine + 25 mM arginine. Haemolymph volume and concentrations of total carbohydrate, trehalose, amino acids, proteins, lipids and percent solids were determined daily through the day preceding larval‐pupal ecdysis. Consumption of diet containing only canavanine resulted in an increased percent haemolymph and consumption of the canavanine‐arginine diet intensified this effect. Thus, percent haemolymph of mature 5th‐instar control larvae was 27% compared to 33% for canavanine and 38% for canavanine‐arginine treated larvae. Treated larvae were unable to maintain the concentrations of carbohydrates, amino acids, proteins and lipids found in controls. Nevertheless, the synthetic mechanisms associated with the release of these compounds into the haemolymph were functioning because their total amounts present in the canavanine and canavanine‐arginine treated larvae were not very different from the control after the additional haemolymph volume was taken into consideration. MODIFICATION DE LA COMPOSITION DE L'HÉMOLYMPHE PAR DES MÉLANGES DE CANAVANINE ET D'ACIDES AMINÉS CHEZMANDUCA SEXTA. La L‐canavanine a des propriétés insecticides puissantes et protège sans aucun doute la plante contre l'activité alimentaire des insectes phytophages. Lorsque l'on nourrit des larves du 5ème stade du ver du tabac Manduca sexta(L.) avec une ration contenant un mélange de canavanine et d'arginine, on obtient des larves géantes. L'augmentation de la biomasse est due à une accumulation de fluides. On a mesuré quotidiennement le volume d'hémolymphe et les concentrations d'hydrates de carbone totaux, de tréhalose, d'acides aminés, de protéines, de lipides et le pourcentage de solides. La consommation d'une ration contenant de la canavanine a causé une augmentation de la quantité d'hémolymphe; cette augmentation a été plus importante dans le cas d'une ration canavanine‐arginine. C'est ainsi que le pourcentage d'hémolymphe était de 27% chez les larves matures du 5ème stade témoins, de 33% chez les larves traitées à la canavanine et 38% chez les larves traitées à la canavanine‐arginine. Les larves traitées ne parvenaient pas à maintenir les concentrations d'hydrates de carbone, d'acides aminés, de protéines et de lipides constatées chez les témoins. Pourtant les mécanismes synthétiques associés à la décharge de ces composés dans l'hémolymphe fonctionnaient, puisque les quantités totales présentes n'étaient pas modifiées.

L-Canavanine, a nonprotein amino acid of certain leguminous plants, manifests potent insecticidal properties in a canavanine-sensitive insect such as the tobacco hornworm Manduca sexta (L.) (Sphingidae). This arginine analog is activated and aminoacylated by arginyl-tRNA synthetase and incorporated into nascent polypeptide chains to create structurally aberrant, canavanine-containing proteins. Analysis of incorporation of [3H]leucine into protein in M. sexta larvae that had been injected with canavanine revealed that this arginine analog stimulates protein synthesis. During the first 3 hr after injection of canavanine, canavanine-mediated net stimulation of protein formation was readily discerned. Thereafter, the stimulation of protein synthesis appeared to be offset by the preferential degradation of anomalous proteins. Double-label protein-turnover experiments with larvae injected with [14C]canavanine- and [3H]arginine-containing hemolymph proteins showed that canavanine-containing proteins were degraded preferentially.

Injection of L-canavanine, a naturally occurring arginine analogue, and of its metabolic derivative, L-canaline, induced almost continuous motor activity in adult tobacco hornworms, Manduca sexta (L.). Initially the moths flew normally, but after a time interval that depended both on the amino acid and on the dose (1−45 μmol/g fresh weight) the moths became disorientated and muscle activity was less patterned. Canaline produced its initial effects 12−30 min after injection, whereas activity in response to canavanine began after a delay of 1−2 h. Canaline (derived from canavanine by an arginase-mediated hydrolytic cleavage) is probably the biologically active factor. Canaline did not affect axonal conduction of action potentials nor the activity of mechanoreceptors on the forewing. Canaline (22μmol/g fresh weight) prolonged the postsynaptic potential of flight muscle fibres, but after 20−40 min. the electrical activity of muscle fibres was normal. The results show that canaline alters the activity of the central nervous system of adult M. sexta, but its mode of action is unknown.