Impact of Phyllocnistis citrella (Lepidoptera: Gracillariidae) on leaf area development and yield of mature citrus trees in the Mediterranean area.

Seasonal population trends and damage to citrus trees by the leafminer Phyllocnistis citrella Stainton were studied in the Valencia area of eastern Spain from 1996 to 1999. The area-wide seasonal flushing pattern of citrus trees and leafminer population trends were determined in 10 mature citrus orchards. In the 10 orchards, the annual percentage of new shoots that developed in the spring ranged from 51 to 96% for individual orchards (mean of 80%). Phyllocnistis citrella populations damaged new leaves from July to November. During this period, approximately 45% of the new leaf area was lost due to leafminer mining. In addition, at three mature citrus orchards, two 'Navelina' sweet oranges from 1996 to 1999 and one 'Clementine' mandarin (variety 'Clemenules') in 1998 and 1999, the leaf area damage, spring flushing pattern, and crop yield were determined in trees sprayed one to three times a year with abamectin (Epimeck, 0.02%) to control P. citrella and compared with nonsprayed control trees. In these three orchards, damaged leaf area in summer-fall flushes was on average 52% in nonsprayed and 8% in sprayed trees. No significant differences were found between sprayed and nonsprayed trees in the spring flushing and flowering pattern, number of fruits or fruit diameter. In Mediterranean areas, P. citrella damaged only 5-15% of the annual new leaf area of mature trees and yield was usually not affected by the pest.