Seasonal Changes of Leaf Damage and Parasitism of the Apple Leaf Miner, Phyllonorycter ringoniella(Matsumura) in Relation to the Management and Varieties in Apple Orchards

Leaf damage rate and actual damaged leaf area by the apple leaf miner (ALM), Phyllonorycter ringoniella(Matsumura), and its parasitism were investigated in 1982 and 1983 in apple orchards. Percent leaf damage was higher in the occasionally sprayed orchards than in the periodically sprayed orchards from May to August, but the trend was reversed after September. Seasonal changes of the leaf damage seemed to be different with the varieties of apple trees. A few species of Eulophidae and Holcothorax testaceipes R. of Encyrtidae were the predominant parasites of the ALM. Overall percent parasitism was highest in the 5th (overwintering) generation, and conspicuously decreased in the 3rd-4th generation (July-August) when insecticides were sprayed periodically. Actual damaged leaf area per mine of the ALM was apparently different with the generations; for the 1st, for the 2nd-4th on the first growth shoot, and for the overwintered generation on the second growth shoot. When ALM leaf damage rate was about , the decrease in the photosynthetic area to the damaged leaf was about .