Oxidative interactions between the spotted alfalfa aphid (Therioaphis trifolii maculata) (Homoptera: Aphididae) and the host plant Medicago sativa

Abstract

AbstractSalivary oxidation has been hypothesized as a possible means by which spotted alfalfa aphid (Therioaphis trifolii maculata (Buckton)) deals with deleterious phenolics in the susceptible host plant, lucerne (Medicago sativa). In this study, some basic questions about this hypothesis were examined. Constitutive flavonoids and a crude phenolic extract from lucerne leaves were shown to be deterrent to the aphid in a choice test. Phenolics were oxidized by phenoloxidase in the saliva of the aphid. Fresh sap expressed from aphid-infested, oxidatively-reactive leaves was phagostimulatory to the aphid, compared to that from non-infested healthy leaves. Oxidative reaction was responsible for at least part of the phagostimulation, since addition of ascorbic acid into the sap deleted the phagostimulatory activity. Ascorbic acid was itself not deterrrent and its titre decreased in leaves after aphid feeding. The results provide further information on the Oxidative interaction between spotted alfalfa aphid and lucerne plants and support the previous suggestion that oxidation of phenolics and anti-oxidation by reductants affects feeding activity of this aphid.