The influence of plant age on resistance of radish to cabbage root fly egg-laying

Cabbage root fly ( Delia brassicae ) egg-laying around radish plants ranging in age from newly emerged seedlings to plants with flowering shoots was studied in the field and laboratory. The attractiveness of radish changed with age, one peak in egg-laying occurring just before plants were of marketable size and further peaks as they produced flowering shoots. The pattern of egg-laying was similar for the six radish cultivars tested, both in the field and laboratory, irrespective of whether flies did or did not have a choice of plants of different ages. At any one age, there was no correlation between egg-laying and plant size. Selection within radish cultivars for the extremes of the range of egg-laying preference appeared to alter the cycle of attractiveness of different radish stocks to cabbage root fly, the response being influenced by environmental conditions.