Effects of field applied residues and length of exposure to tebufenozide on the obliquebanded leafroller (Lepidoptera : Tortricidae)

Studies were conducted with the obliquebanded leafroller, Choristoneura ros aceana (Harris), and tebufenozide to determine the influence of various fac tors on the efficacy of this insecticide under field conditions. Larvae wer e exposed to apple foliage collected from commercial orchards at different intervals after insecticide applications. Mortality of neonates on actively growing (terminal) and mature (spur) foliage 10 d after an airblast spraye r application of tebufenozide was 0 and 35-74%, respectively. Feeding by la rvae was also assessed on collected foliage. There was significantly less f eeding oil tebufenozide-treated foliage than chlorpyrifos- and nontreated f oliage (P < 0.05). In the second study, to determine the efficacy of tebufe nozide in the absence of larval movement to terminals with sublethal residu es, terminal foliage with obliquebanded leafroller larvae was collected fro m two commercial orchards 24 h after an airblast sprayer application of teb ufenozide. After larvae were confined on this terminal foliage in the labor atory for 10 d, mortality was > 90%. In the third study, to examine the eff ects of obliquebanded leafroller movement to foliage with sublethal residue s, we designed a laboratory bioassay in which larvae were exposed to foliag e treated with tebufenozide and transferred to untreated foliage after vari ous exposure intervals. The higher the concentration of tebufenozide, the l ess exposure time was necessary to cause high levels of mortality of neonat es. The terminal feeding behavior of obliquebanded leafroller larvae, low r esidues on terminal foliage before the end of the typical 2-wk spray interv al, and the length of exposure necessary for high levels of mortality may d ecrease the effectiveness of tebufenozide for obliquebanded leafroller cont rol.