Abstract

Levels of primary nutrients (protein and carbohydrate) and secondary metabolites vary both within and between trembling aspen trees ( Populus tremuloides ), and affect the feeding behaviour and performance of forest tent caterpillars ( Malacosoma disstria ). The relationships between primary nutrient content, insect performance and dietary preference were studied using both artificial and natural diets. In experiments with artificial diets of controlled nutritional content, compensatory feeding abilities were tested. Caterpillars were deprived of either protein or digestible carbohydrate to determine whether they exhibit compensatory dietary self-selection when given a choice between foods containing previously absent nutrients. In experiments using natural foods, caterpillar performance and choice behaviour were tested using leaves treated with different nutrient-boosting supplements: protein, carbohydrate, and a neutral control. Caterpillars appeared to regulate for carbohydrate deficiencies only. When given a choice between artificial carbohydrate- or protein-only diets, caterpillars took less time to contact the carbohydrate diet, and consumed more upon first contact, suggesting an olfactory and phagostimulatory response to carbohydrate. In the absence of choice, caterpillars ate most and gained the most weight on a diet containing both protein and carbohydrate. When given a choice between leaves, caterpillars showed no initial preference, but with prolonged exposure ate more of the control leaf, followed by the carbohydrate leaf. Under no-choice conditions, caterpillars on the control leaf experienced the shortest instar duration and greatest growth rate, while on the carbohydrate leaf they exhibited increased survival. These findings suggest that carbohydrate concentration is the principal factor in forest tent caterpillar food choice.