The 3 key lepidopterous pests of cruciferous crops, Artogeia rapae [Pieris rapael, Plutella xylostella and Trichoplusia ni, were monitored throughout the growing season at several locations in Washington and Oregon in 1986 and 1987 on collard [We] plants. Populations of these pests differed markedly from location to location and between years. Pieiis rapae was the most abundant, Plutella xylostella was next in abundance, and T. ni the least abundant, and on many dates the latter was not observed. Seven species of parasitoids were recovered and rates of parasitism varied significantly over time and among locations. Diadegma insularis was the most abundant parasitoid of P. xylostella. It parasitized up to 100% (range 0-100) and accounted for 74-100% of total parasitism. Cotesia rubecula was the dominant species attacking Pieris rapae in Washington (0-50% parasitism) and accounted for 32-100% of total parasitism. 'Me only parasitoid species recovered from T. ni was Voria ruralis, which parasitized 0-14% of larvae. none