Oxidases in the gut of an aphid, Macrosiphum rosae (L.) and their relation to dietary phenolics

Abstract

Catechol oxidase (EC 1.10.3.1) and peroxidase (EC 1.11.1.7) were detected in the gut of the rose aphid. Both enzymes also occur in the saliva and catalyse the oxidation of catechin, a feeding deterrent that occurs in the parenchymal and vascular tissues of the rose. The oxidation products of catechin are phagostimulant, however, and the aphids will feed on tissues and on aqueous diets containing low concentrations of catechin. No catechin was detected in the gut, haemolymph or honeydew of aphids collected from roses but the presence in the gut and honeydew of phenolics that differed from those in the haemolymph was consistent with the ingestion and intraintestinal conversion of phenolics of plant origin. Evidence of the presence of catechin in the phloem sap was obtained, but whether the insects ingested phenols exclusively from phloem sap or from other tissues as well remained uncertain.