Linking Insecticide Bioassays with Residue Analyses To Evaluate Control of Platynota idaeusalis (Lepidoptera: Tortricidae) Neonates on Apple: Single Spray

Abstract

Evaluation of the insecticides azinphos-methyl, chlorpyrifos, and methomyl for control of Platynota idaeusalis (Walker) neonates on apple foliage was conducted during August and September 1987 under a series of alternate-row middle and complete (chlorpyrifos only) sprays. Insecticide residues on the unsprayed side of the tree ranged from 9 to 22% on 4 August (immediately following first spray) and 21 to 58% on 1 September (immediately following fifth spray) compared with the sprayed side, respectively. Levels of residue on the sprayed side of the tree 6 d after spraying increased following each of the first three alternate-row middle sprays. Residue levels of azinphosmethyl and methomyl declined following the fourth spray after > 20 mm of precipitation, but increased again following the fifth spray. Half-lives of insecticide residues following the fifth spray were ≈ 7 d for azinphos-methyl, 3-4 d for methomyl, and < 1 d for chlorpyrifos. Field-collected larvae were more tolerant to azinphos-methyl and chlorpyrifos than a laboratory colony (LR50s were 8 and 17 times greater, respectively). No difference in response between strains was found with methomyl. Levels of fruit injury by P. idaeusalis at harvest on trees treated with seasonlong programs of azinphos-methyl, chlorpyrifos, or microencapsulated methyl parathion alone were not significantly different from trees left untreated. Seasonlong use of methomyl either alone or in combination with an organophosphate significantly reduced fruit injury.