EFFECT OF 2ND-STAGE IPM PRACTICES ON PARASITISM OF APPLE BLOTCH LEAFMINER (LEPIDOPTERA, GRACILLARIIDAE) LARVAE IN MASSACHUSETTS APPLE ORCHARDS

In 1989 and 1990, parasitism of the apple blotch leafminer, Phyllonory cter crataegella (Clemens), was assessed in 17 and 16 apple orchards, respectively, in Massachusetts to determine the effect of integrated p est management (IPM) practices that reduced pesticide use between earl y June and late August. In test blocks on each farm, broadcast pestici de applications for control of the apple maggot, Rhagoletis pomonella (Walsh), were replaced by use of either red spherical sticky traps on perimeter apple trees to intercept immigrating apple maggot flies or b y applications of pesticides to perimeter apple trees. In either case, no insecticides or miticides were applied to the interior of test blo cks after early June. Use of these methods was designed as second-stag e IPM, and apple blotch leafminer parasitism under such management was compared with an adjacent block in each orchard using conventional pe sticide tactics. Average parasitism of tissue-feeding apple blotch lea fminer larvae across all orchards was slightly greater in the second a nd third host generations in blocks in which second-stage IPM practice s were used than in conventionally managed blocks on the same farms. M ost enhancement of apple blotch leafminer parasitism occurred in orcha rds in which traps were used to control apple maggot flies. Orchards i n which perimeter-pesticide applications were made showed little or no difference in parasitism levels from those of full spray blocks. None of six orchard or insect variables examined (block size, ratio of int erior trees to edge trees, nature of surrounding vegetation, number of pesticide applications per leafminer generation, density of tissue-fe eding stage apple blotch leafminer mines, or percentage parasitism in the previous apple blotch leafminer generation) explained a significan t proportion of the variation in parasitism seen among orchards and bl ocks in correlation analyses. Suppression of first generation apple bl otch leafminer densities in 1990 was followed by lower average parasit ism across orchards compared with 1989.