BEHAVIORAL AND OLFACTORY VARIATIONS IN THE LEEK MOTH, ACROLEPIOPSIS-ASSECTELLA, AFTER SEVERAL GENERATIONS OF REARING UNDER DIVERSE CONDITIONS

Three strains of the leek moth, Acrolepiopsis assectalla, were compare d: 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 res ponsiveness (L, G2 and D) were compared between individuals subjected to leek leaf odour and 4 volatiles identified in these leaves: 2 speci fic 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 thio sulphinate, and cis-3-hexen-1-ol were lower for L than for D females. The chemoanemotactic responses to dipropyl disulphide are almost ident ical, 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 thres hold for thiosulphinate was at a concentration (v/v) of 4 x 10(-4) M/I for D females, 4 x 10(-5) M/I for L females and 4 x 10(-8) M/I for G2 ones. It may be hypothesised that laboratory rearing conditions cause variations in the thresholds of antennal sensitivity and walking beha viour to specific and more efficient leek volatiles. This may result f rom the selective pressures experienced by the larvae reared in the la boratory.