Meeting Abstract
Population dynamics of herbivorous insects are strongly correlated with climate, largely through the influence of temperature on physiological processes and rainfall on food quality. Using Australian plague locusts, we have quantified diet quality across its temperature range. Rates of development are most influenced by temperature, and growth by diet. The slowest developing and smallest insects occurred when feeding on diets high in carbohydrate and low in protein, and when ingestion rates were most reduced. While diet quality at any given temperature can be quantified using chemically defined foods, measuring the chemical composition of leaves does not provide an indication of the quality of that leaf to an insect herbivore. From a range of native and improved pasture grasses we found the rate protein and carbohydrate were supplied, varied independently and non-linearly with temperature. Typically, Australian plague locusts were able to gain an optimal ratio of protein to carbohydrate at their thermal optima because at this temperature protein was extracted with lowest efficiency but carbohydrate with highest efficiency. However, the rates of supply of all nutrients scaled in a plant specific manner with temperature. Thus, host plant quality is temperature dependent, or conversely, dietary fitness is optimized at a specific temperature for a given plant. These results highlight the complexity of ecological interactions. For highly mobile insects such as locusts, what may appear to be a nutritional complex environment may not be, if there is thermal heterogeneity.
