Insecticide Resistance in the Light Brown Apple Moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae): Larval Response to Azinphosnlethyl

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Abstract
Azinphosmethyl resistance in the light brown apple moth Epiphyas postvittana (Walker) was confirmed with four methods: topical application of larvae, a Potter tower direct-spray method, and two residue exposure methods using middle instars and newly hatched larvae. The Mariri population exhibited a 140-fold resistance factor, using topical application of larvae. A 20-fold resistance factor was obtained by using a Potter tower to spray the insects directly. The first residue exposure method, using a Potter tower to treat apple leaf discs with the 50 WP formulation, produced a 13-fold resistance factor when third- and fourth-instar larvae were caged on the discs for 48 h. In the second residue exposure method, when first-instar larvae were caged onto leaf discs for 16 h, the resistance factor was 5-fold. The Potter tower, acetone-spray method was found to be the most satisfactory technique for evaluation of azinphosmethyl resistance in larvae. The application of this technique for monitoring resistance in the field is suggested.