COMPARISON OF FEEDING-BEHAVIOR OF 2 BRASSICA PESTS BREVICORYNE-BRASSICAE AND MYZUS-PERSICAE ON WILD AND CULTIVATED BRASSICA SPECIES

Feeding behaviour of the specialist Brassicae aphid, Brevicoryne brass icae (L) (cabbage aphid) and the generalist, Myzus persicae, (Sulzer) (peach potato aphid) was monitored electronically on the susceptible c auliflower, Brassica oleracea var. botrytis cv Newton Seale, and a ran ge of 17 Brassica species, B. carinata, B. juncea, B. nigra, B. macroc arpa, and B. villosa vac drepanensis and cultivated brassica varieties , B. oleracea, B. campestris and B. napus. Aphids, monitored for 10 h on the underside of leaves, performed recognisable feeding behaviour o n all brassica species. The main differences in feeding behaviour, bet ween M. persicae and B. brassicae, on the susceptible cauliflower Newt on Seale, were fewer probes, shorter times to initially reach the phlo em but longer times to establish sustained phloem ingestion and the lo nger times spent, by M. persicae, in xylem ingestion. Feeding behaviou r on the range of brassica species tested indicated that generalist an d specialist aphids are influenced differently by the host plant. A lo nger time spent in xylem ingestion was again the major difference in t he feeding behaviour of the two aphids. In addition, rejection of pass ive phloem ingestion, by M. persicae, was not related so closely to in creased time spent in non probing activities, as for B. brassicae. Thi s observation indicates that M. persicae does not generally accept or reject brassica species due to the presence of phagostimulants, such a s glucosinolates at the leaf surface or along the stylet pathway, unle ss the concentration is very high. Differences in feeding strategies e mployed by generalist and specialist aphids on the same plants are dis cussed.