The seasonal distributions of eggs and first-, second-, and third-instar larvae of the western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), in sweet cherries were determined at three sites in central Washington in 2002 and 2003. The egg was the major stage during early, mid and late season. The distributions of eggs (i.e., the percentages of total immature stages that were eggs) were similar all season, but those of first, second and third instars were greatest in late season. First, second and third instars occurred in similar numbers in 2002, but third instars were the most abundant in 2003. Tree quadrant had no effect on egg and larval densities and distributions. The majority of infested fruit had only one egg or larva, but there were significant increases in percentages of fruit with two or ≥ three eggs or larvae as percentages of fruit that were infested increased during the season. When there were two larvae in a fruit, one was larger than the other in 90.8% of cases. Results indicate time of season but not location within trees (1.5 to 2 m above ground) has differential effects on egg and larval distributions in fruit and on female oviposition behaviors that may result in multiple infestations and larval interactions. Seasonal effects on immature stages are probably related to developmental times and stage-specific mortality; whereas, effects on adults may be related to reduced availability of unoccupied fruit for oviposition.

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