Feeding damage by Diuraphis noxia results in a nutritionally enhanced phloem diet

The feeding behavior of Diuraphis noxia Mordvilko (Homoptera: Aphididae) on susceptible hosts causes both ultrastructural and tissue level damage whic h may affect phloem composition. Genetic evidence suggests that endosymbiot ic bacteria in most aphids overproduce limiting amino acids to benefit host s but that D. noxia depends less on endosymbionts for these nutrients, poss ibly due to an enriched diet. To determine whether D. noxia feeding damage results in higher concentrations of essential amino acids, stylet exudates were analyzed from wheat (Triticum aestivum) damaged to different degrees. Comparison of samples from undamaged and damaged susceptible wheat revealed changes in amino acid composition and an increase in levels of essential a mino acids, indicating a nutritionally enhanced ingesta. The changes in sty let exudates paralleled changes in leaf exudates, indicating that the effec ts are systemic. Feeding damage is not observed on a resistant wheat host, var. Halt, and leaf exudates from infested Halt did not show changes in ami no acid composition. Mean relative growth of nymphs was significantly lower on Halt than on susceptible Arapahoe, indicating that Halt is a less suita ble host. Both varieties show similar amino acid levels in non-infested sam ples, suggesting that D. noxia infestation does not enhance the phloem envi ronment in Halt. This study provides evidence that aphid feeding can genera te a nutritionally enhanced phloem diet.