title: Influence of dietary nutritional composition on caterpillar salivary enzyme activity.
abstract: Caterpillars are faced with nutritional challenges when feeding on plants. In addition to harmful secondary metabolites and protein- and water-limitations, tissues may be carbohydrate-rich which may attenuate optimal caterpillar performance. Therefore, caterpillars have multiple strategies to cope with surplus carbohydrates. In this study, we raise the possibility of a pre-ingestive mechanism to metabolically deal with excess dietary sugars. Many Noctuid caterpillars secrete the labial salivary enzyme glucose oxidase (GOX), which oxidizes glucose to hydrogen peroxide and gluconate, a nutritionally unavailable carbohydrate to the insect. Beet armyworm, Spodoptera exigua, larvae were restricted to diets varying in protein to digestible carbohydrate (P:C) ratio (42p:21c; 33p:30c; 21p:42c) and total nutrient concentration (42% and 63%). High mortality and longer developmental time were observed when caterpillars were reared on the C-biased, P-poor diet (21p:42c). As the carbohydrate content of the diet increased, caterpillars egested excess glucose and a diet-dependent difference in assimilated carbohydrates and pupal biomass was not observed, even though caterpillars restricted to the C-biased diet (21p:42c) accumulated greater pupal lipid reserves. Larval labial salivary GOX activity was also diet-dependent and gluconate, the product of GOX activity, was detected in the frass. Unexpectedly, GOX activity was strongly and positively correlated with dietary protein content.
authors.affiliation: Department of Plant Science, McGill University, 21,111 Lakeshore, Ste-Anne-de-Bellevue, Québec, Canada H9X 3V9.
authors.forename: Branislav
authors.initials: B
authors.lastname: Babic
authors.forename: Alexandre
authors.initials: A
authors.lastname: Poisson
authors.forename: Shireef
authors.initials: S
authors.lastname: Darwish
authors.forename: Jean
authors.initials: J
authors.lastname: Lacasse
authors.forename: Magali
authors.initials: M
authors.lastname: Merkx-Jacques
authors.forename: Emma
authors.initials: E
authors.lastname: Despland
authors.forename: Jacqueline C
authors.initials: JC
authors.lastname: Bede
mesh_terms: D000704:Analysis of Variance; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D004040:Dietary Carbohydrates / Q000378:metabolism*; D004044:Dietary Proteins / Q000378:metabolism; D005949:Glucose Oxidase / Q000378:metabolism*; D007814:Larva / Q000201:enzymology / Q000254:growth & development; D009036:Moths / Q000201:enzymology*; D012469:Salivary Glands / Q000201:enzymology*
chemical_list: D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D005949:Glucose Oxidase