THE RELATIVE IMPORTANCE OF GLUCOSINOLATES AND AMINO-ACIDS TO THE DEVELOPMENT OF 2 APHID PESTS BREVICORYNE-BRASSICAE AND MYZUS-PERSICAE ON WILD AND CULTIVATED BRASSICA SPECIES

This paper describes an experiment to investigate the relative importa nce of glucosinolates and the availability of free amino acids in the phloem to the feeding behaviour and development of the specialist bras sica aphid, Brevicoryne brassicae (L) (cabbage aphid) and the generali st, Myzus persicae, (Sultzer) (peach potato aphid). Aphid development was determined on brassica species and cultivated brassica varieties. Analysis of individual glucosinolates in the wild brassica species ide ntified significant differences in their profiles and in their concent rations present in freeze dried leaves. Multiple regression analysis s howed a significant correlation (r = 0.83) between the intrinsic rate of increase of B. brassicae and glucosinolate concentrations; four glu cosinolates, 2-OH-3-butenyl, and 2-propenylglucosinolate, 3-methoxyind olyl and 4-pentenylglucosinolates accounted for 79% of the variation. The intrinsic rate of increase of M. persicae was less correlated, tho ugh still significant (r = 0.5); 3-indolyglucosinolate and 3-butenylgl ucosinolate accounted for 47% of the variation. Regression analysis al so showed a correlation between phloem amino acid concentrations and t he intrinsic rate of increase of B. brassicae (r = 0.48) but not of M. persicae. The concentration of the important amino acids tyrosine, al anine, leucine and glutamic acid, accounted for 43% of the variation i n intrinsic rate of increase. Leaf water potential of the Brassica spe cies showed no relationship with the intrinsic rate of increase of eit her B. brassicae or M. persicae.