In Y-tube olfactometer tests, female Cotesia plutellae Kurdjmov (Hymenoptera: Braconidae), a major parasitoid of Plutella xylostella (L.) in southeast Asia, preferred the odour of the brassica type (Blue Lake cabbage) on which they had developed. Such plants were even preferred to the odour of caterpillar-infested and damaged leaves of another brassica (Early Phenomenal cauliflower). However, within one brassica type, the odour of caterpillar-infested leaves was preferred to that of uninfested and undamaged leaves. Odours of both Blue Lake and Early Phenomenal were preferred to the control odour (water). However, following the transfer of the parasitoid from Blue Lake to another cabbage (Brunswick) for one generation, females no longer distinguished between Blue Lake and Early Phenomenal.