NUTRIENT REGULATION IN THE PEA APHID ACYRTHOSIPHON-PISUM - APPLICATION OF A NOVEL GEOMETRIC FRAMEWORK TO SUGAR AND AMINO-ACID CONSUMPTION

A recently developed framework was applied to investigate the responses of newborn pea aphids, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), to simultaneous variations ip dietary sucrose and amino acid levels. The location of functional 'targets' for intake and growth were determined experimentally using performance criteria. Behavioural rules employed by insects to approach these targets were investigated by reference to the geometry of arrays of intake and growth across a range of diets. First-instar aphids were fed one of thirty-one chemically-defined diets ranging in sucrose concentration from 200 to 1000 mm and amino acid concentration from 25 to 250 mm. Insect survivorship, dry weight, protein- and carbohydrate-derived growth were high for all diets except those with the lowest nutrient levels. Peaks in final dry weight and protein content identified the intake target as the point reached by larvae fed the 600 mm sucrose, 75 mm amino acid diet. Aphids regulated sucrose primarily by consumption (i.e. behaviourally), whereas amino acids were regulated post-ingestively (i.e. by physiological mechanisms).