Three strains of the leek moth, Acrolepiopsis assectella, were compared: two reared on leek leaves (Allium porrum) for which generations 10 to 12 (L) or generation 2 (G2) were used, the third one (D) reared on an artificial diet incorporating leek powder, for which generation ca 140 was examined. The walking behaviour (L and D) and the antennal responsiveness (L, G2 and D) were compared between individuals subjected to leek leaf odour and 4 volatiles identified in these leaves: 2 specific sulphur ones (dipropyl thiosulphinate and dipropyl disulphide) and 2 'general green leaf volatiles' (cis-3-hexen-1-ol and trans-2-hexen-1-ol). The walking behavioural thresholds to leek odour, dipropyl thiosulphinate, and cis-3-hexen-1-ol were lower for L than for D females. The chemoanemotactic responses to dipropyl disulphide are almost identical, and trans-2-hexen-1-ol has nearly no activity. Accordingly, the olfactory sensitivity (assessed by EAG) to sulphur volatiles and cis-3-hexen-1-ol was higher for L and G2 females than for D ones. The threshold for thiosulphinate was at a concentration (v/v) of 4 10 ,4 M/l for D females, 4 10 ,5 M/l for L females and 4 10 ,8 M/l for G2 ones. It may be hypothesised that laboratory rearing conditions cause variations in the thresholds of antennal sensitivity and walking behaviour to specific and more efficient leek volatiles. This may result from the selective pressures experienced by the larvae reared in the laboratory.