Effect of phenolics from woody plants on activity of grain aphid oxidases

Changes in activity of the grain aphid peroxidase (Px) and polyphenol oxidase (PPO) towards phenolics isolated from leaves of black currant, sour cherry and walnut were examined. Slight increase in activity of peroxidase was found within insect tissues after 24 h of walnut extract treatment, whereas black currant and sour cherry strongly inhibited activity of this enzyme. Later on, the walnut extract reduced activity of the enzyme, finally about 30%. The other extracts showed slight changes in Px activity. The grain aphid’s polyphenol oxidase was stimulated during the first 24 h of the experiment. Further treatment with the phenolics extracts reduced activity of the grain aphid polyphenol oxidase. Generally, phenolics isolated from the black currant and sour cherry were more effective in reducing activity of the aphid peroxidase, whereas phenolics from walnut reduced the polyphenol oxidase activity. Possible application of the phenolics isolated from the woody plants as modern biopesticides towards the grain aphid is discussed.