ASCORBIC ACID, ASCORBATES AND ANALOGS IN SPODOPTERA LITTORALIS DIET: STABILITY AND EFFECT ON LARVAE

Abstract

The dietary effect of L‐ascorbic acid, its ascorbates and analogs at equimolar concentrations on larvae and pupae of the Egyptian Cotton Leafworm, Spodoptera littoralis (Boisd.) was studied. The daily activity loss of these compounds in the diet was determined with a 2,4 dinitrophenylhydrazine‐thin layer chromatography method. This determination of ascorbates and analogs showed a rapid loss of activity down to about 50% after 4 days. However, ascorbic acid was significantly more stable. Storing ascorbic acid, its ascorbates and analogs at 6° only preserved their activity at 10–25% more than at 25°; sodium ascorbate, calcium ascorbate and L‐dehydroascorbic acid equalled the activity of L‐ascorbic acid in larval and pupal weight, as well as insect development. D‐araboascorbic acid (= D‐isoascorbic acid) did not support the normal insect development. Stability of ascorbic acid ascorbates and analogs in the diet in relation to their dietary effects is discussed. RÉSUMÉ EFFETS DE L'ACIDE ASCORBIQUE, D'ASCORBATES ET D'ANALOGUES DANS L'ALIMENTATION DE SPODOPTERA LITTORALIS: STABILITÉ ET EFFET SUR LES LARVES Ce travail étudie les effets sur les larves et les nymphes de Spodoptera littoralis (The Egyptian Cotton Leafworm), d'adjonction à l'alimentation d'acide L‐ascorbique et de ses ascorbates et analogues à des concentrations équimoléculaires. Les pertes journalières d'activité de ces composés ont été déterminées par une méthode de chromatographie sur couches minces avec le 2–4 dinitrophenylhydrazine. Cette détermination des ascorbats et analogues a révélé une perte rapide d'activité jusqu'à environ 50% après 4 jours. Cependant l'acide ascorbique est relativement plus stable. Le stockage à 6° de l'acide ascorbique, de ses ascorbates et analogues préservait leur activité de seulement 10–25% de plus qu'à une température de 25°. L'ascorbate de sodium, l'ascorbate de calcium et l'acide L‐dehydroascorbique montraient une activité égale à celle de l'acide L‐ascorbique, quant à leur effet sur le poids des larves et pupes, aussi bien que sur le développement de l'insecte. L'acide D‐ascorbique ne permet pas le développement normal de l'insecte. La stabilité de l'acide ascorbique, des ascorbates et des analogues dans l'aliment est discutée en rapport avec les effets observés.

Vitamin C content in plants is modified by insects and influences susceptibility to herbivory

“…It should be noted that studies utilizing artificial diets may over-estimate insects' dietary requirements because AsA rapidly degrades. Unless the diet is frequently replaced, its AsA content may be much lower than estimated at the time of preparation [34,35]. Additionally, some of the benefits of incorporating AsA into artificial diets may be due to increased stability of other nutrients such as linolenic acid [36].…”

The reproductive capacity of Spodoptera littoralis moths fed ascorbic acid analogs

“…In the larva this oxidized form of vitamin C was as active as L-ascorbic acid in the diet, whereas D-isoascorbic acid did not support larval development (Navon, 1978). In the larva this oxidized form of vitamin C was as active as L-ascorbic acid in the diet, whereas D-isoascorbic acid did not support larval development (Navon, 1978).…”

“…L-dehydroascorbic acid did not reduce the moths' reproductive capacity. In the larva this oxidized form of vitamin C was as active as L-ascorbic acid in the diet, whereas D-isoascorbic acid did not support larval development (Navon, 1978). In Manduca sexta larvae, L-dehydroascorbic acid was fully active, the bromo analog and D-ascorbic acid were partially active and D-isoascorbic acid was inactive in supporting larval growth (Kramer & Seib, 1982).…”