Validation of a Field Monitoring System for BPU-Type IGR Resistance in the Diamondback Moth, Plutella xylostella-Presumed Working Scheme Based on IRAC Method No. 7 (Leaf Dipping Method)

Abstract

Results of the IRAC Method NO.7 (leaf dipping method) were compared to those of the spray tower method in aspect of the resistance of diamondback moth (DBM), Plutella xylostella, to benzoylphenyl urea (BPU)-type insect growth regulators (IGR). The leaf dipping method resulted in 3.29-fold higher BPU-IGR deposit than the spray tower method. The treating period of leaf dipping lasts from 3rd instar to pupation, which is longer than the 48-hour period in the spray tower method. Both the higher dosage and the longer treating period of leaf dipping had resulted in higher sensitivity of the DBM to the treated doses of BPU-type IGR compared to the spray tower method. No anti-feeding effect of BPU-type IGR against DBM was observed. The susceptibility of a susceptible strain to 4 BPUs, chlorfluazuron, teflubenzuron, hexaflumuron and flufenoxuron, had been determined by using the leaf dipping method. The reproducibility of this method was tested and substantiated by comparing LC(subscript 50S) in the n and n+6 generations of the susceptible strain. The ability of leaf dipping method in detecting the BPU resistance in DBM was verified by the Independent Student's t-distribution test, which confirmed the separation of LC(subscript 50S) of the susceptible strain from 3 BPU-resistant strains at 95% fiducial limits. We concluded that four to five IGR concentrations in 10-fold increments with water are sufficient for testing BPU-resistance in DBM, except for hexaflumuron, the increment should be adjusted to 4-5 fold. The leaf dipping method is not suitable for synergistic with piperonyl butoxide (PB) due to different methods were applied to the DBM.