Fruit damage by obliquebanded leafroller, Choristoneura rosaceana (Harris), was examined on four different apple cultivars during 1997–1999 in heavily infested orchards in New York State. Initial fruit damage occurred 354 ± 26 degree-days base 6°C (DD₆) after the first moth catch from the overwintering generation and continued to increase until after the typical spray season (≈1,300 DD₆). In addition to apple damage by late instars, fruit damage occurred by early instars of the summer and overwintering generations. The insect growth regulator tebufenozide was used as a model insecticide to determine how a slow-acting insecticide and its relative toxicity to early (neonate) and late (fourth and fifth) instars may influence the efficacy of sprays for the control of the obliquebanded leafroller. Because tebufenozide is a slow-acting compound, bioassays were conducted to determine what percentage of the total mortality to neonates occurs at each 24 h interval until 10 d. Based on a polynomial regression, half of the total mortality to larvae at the LC₂₅, LC₅₀, LC₉₀, and LC₉₉ occurred at 7.2, 5.0, 4.1, and 3.0 d, respectively. Late instars were three times more tolerant to tebufenozide than neonates.