The effect of leaf excision on the performance of Myzus persicae and Brevicoryne brassicae in relation to the nutrient treatment of the plants

Two groups of brussels sprout plants of one variety given different fertilizer treatments proved ‘resistant’ and ‘susceptible’ to both Myzus persicae and Breicoryrie brassicae, as measured by aphid mean relative growth rate. The hypothesis that leaf disc would fail to reflect differences in ‘nutritionallybased’ plant resistance was confirmed with B.brussicue but not M.persicae. Both aphids grew more slowly on discs than leaves of ‘susceptible’ plants; the reverse tendency showed on ‘resistant’ material. Total:(, amino nitrogen proved poorly correlated with aphid performance. Previously published (van Emden & Bashford, 1971) equations relating individual amino acids to aphid performance gave a better fit to the results, but still failed to account for the reduced performance of the aphids on ‘susceptible’ discs.