Populations of the diamondback moth, Plutella xylostella (L.), were collected from fields of crucifer vegetables in the USA and Mexico from 2001 to 2003 for baseline susceptibility tests and resistance monitoring to three new insecticides (spinosad, indoxacarb and emamectin benzoate). Most populations were susceptible to all three insecticides, but resistance to spinosad extended from Hawaii (2000) to Georgia (2001) and California (2002) and a population from Hawaii in 2003 showed high levels of resistance to indoxacarb. When spinosad, indoxacarb and Bt were used simultaneously in a mosaic fashion in a greenhouse cage experiment, the overall resistance development in diamondback moth was more rapid compared with other treatments when these products were used in a rotation strategy. Proactive resistance monitoring and management programs are vital for sustainable use of a new insecticide for diamondback moth control.