Nutritional Ecology Of Plant Feeding Insects

NUTRITIONAL ECOLOGY OF PLANT FEEDING INSECTS

(Or: “What do Insects Need, and Where’s (& How) the Best Place to get It?”)

I. Insect Nutritional Requirements A. Carbohydrates: Polyhedroxyl aldehydes & ketones 1. Classifications a. Mono-, di-, oligo-, poly- saccharides b. Pure, Derived, Conjugated 2. Use: Very similar to mammals a. Energy b. Vitamin synthesis c. Structure: Particularly chitin, Some pigments (protection) d. Storage, cold hardiness, pheromone synthesis d. Defensive compounds 3. Unutilizable & toxic carbohydrates a. Ripe berries often rich in sorbose (unutilizable by insects) b. 5-C sugars often toxic: Galactose Arabinose B. Lipids: Polyunsaturated fatty acids & sterols 1. Use a. Structural compounds: cell membranes, cuticle b. Source of metabolic energy: Linked to flight behavior c. Water conservation 2. Absolute requirements a. Polyunsaturated fatty acids: C18 b. Sterols: 1. Structure 2. Endocrine system: Ecdysone precursor 3. Carrier Molecules: Lipoproteins C. Proteins: 1. Uses: extremely broad range a. Structure, enzymes, DNA & RNA, storage, etc. b. Bioluminescence, Silk 2. Requires dietary Nitrogen 3. Some N containing compounds are toxic: Alkaloids, cyanogenic glycosides, etc. D. Water E. Vitamins & Micronutrients: Coenzymes (K,P, Mg, Zn, Fe, Mn, Ca)

II. Insect Nutritional Physiology A. Digestion & Excretion 1. Carbohydrates a. Digestion: Simple carbohydrases b. Excretion 2. Lipids: Simple hydrolysis 3. Proteins: Enzymes (sensitive to Ph, etc.) B. Nutritional Indices: Waldbauer 1968 1. Definitions Relative Growth Rate (RGR) = Biomass Gain/Original size per day Biomass Gain = Ingested - Feces - Metabolism Relative Consumption Rate (RCR) = Food Ingested/Original size per day Approximate Digestibility (AD) = (Ingested - Feces)/Ingested Efficiency of Conversion of Digested Food (ECD) = Biomass G/I-F Efficiency of Conversion of Ingested Food (ECI) = Biomass G/I

RGR = RCR * ECD * AD ECI = AD * ECD

2. Homeostasis C. The dilemma to eating plants: N availability; Implications III. Variable Distribution of Nutrients: Nitrogen A. Plant Taxa B. Plant Part Storage tissues (seeds) > Organs with high turnover rates (Flowers, fruits, leaves, cambium > Saps: (Phloem > xylem sap) > Wood C. Plant Phenology: Plant Age, Tissue Age D. Environmental Conditions E. Interactions with Allelochemicals

Water A. Plant Taxa Forbs> Grasses> Shrubs> Trees B. Plant Part 1. Foliage > wood C. Plant Phenology: Younger tissue has higher water content D. Environmental Conditions

Variations in insect performance on different plant parts & taxa Approximate digestibilities: tree foliage > forb foliage ECI’s; AD’s Seeds, Pollen > Leaves > Wood

IV. Mechanisms for contending with low Nitrogen Availability A. Higher food consumption or development time B. Specialized digestive systems & symbiotic relationships 1. Elongated side pouches (caecae) house bacteria, yeasts, protozoa 2. External symbionts C. Occasional cannibalism & carnivory D. Switching among plant parts E. Regulation of plant chemistry

V. Implications of Variable Nutrient Quality A. Plant Defense Theory 1. Induced Defenses 2. Interactions with Allelochemicals 3. Plant Stress Theory 4. Low nutritional quality as a form of defense? Berenbaum B. Natural & Sustainable Resource Management 1. Breeding for high quality plants 2. Fertilization & Irrigation 3. Acid Precipitation: