Survival of artificial cohorts of larvae of the imported cabbageworm, Pieris rapae (L.), was assessed in a collard (Brassica oleracea L., var. acephala) patch on an organic vegetable farm in western Massachusetts. We recorded a significant drop in survival of larvae between the 4th and 5th instar due to parasitism by the parasitoid Cotesia rubecula (Marshall), which was introduced to New England from China in 1988. This was a large change from the survivorship pattern of P. rapae observed in the same area in 1985–1986, in which there was a significant drop in survival between 5th instars and pupae due to Cotesia glomerata (L.), the dominant parasitoid of P. rapae in New England at the time. In our study, parasitism by C. rubecula averaged 62.4 ± 8.6%, while no parasitism by C. glomerata was observed. The introduction of C. rubecula is now very likely to be benefitting organic vegetable producers in western Massachusetts, killing more larvae and at an earlier life stage than the previous parasitoid, reducing the potential for damage to cole crops.