Apple damage, pest phenology, and factors influencing the efficacy of tebufenozide for control of obliquebanded leafroller (Lepidoptera : Tortricidae)

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 degreesC (DD6) after the first moth catch from the o verwintering Generation and continued to increase until after the typical s pray season (approximate to1,300 DD6). In addition to apple damage by late instars, fruit damage occurred by early instars of the summer and overwinte ring generations. The insect growth regulator tebufenozide was used as a mo del insecticide to determine how a slow-acting insecticide and its relative toxicity to early (neonate) and late (fourth and fifth) instars may influe nce the efficacy of sprays for the control of the obliquebanded leafroller. Because tebufenozide is a slow-acting compound, bioassays were conducted t o determine what percentage of the total mortality to neonates occurs at ea ch 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 tol erant to tebufenozide than neonates.