INTERACTIONS BETWEEN THE DIAMONDBACK MOTH, PLUTELLA-XYLOSTELLA L AND GLASSHOUSE AND OUTDOOR-GROWN CABBAGE CULTIVARS

Interactions between Brassica cultivars (cvs) and adult and larval sta ges of Plutella xylostella L. were examined. In six-way choice oviposi tion experiments, glasshouse-grown Chinese cabbage cv. Tip Top was pre ferred to five outdoor-grown temperate cabbage cultivars but was simil ar to four out of five tropical cultivars. Bionomic studies with neona te larvae on temperate cabbage cultivars showed that mean larval durat ion was longer and percentage survival less on older compared with you nger plants but that plant age or cultivar had little effect on pupal weight. The fecundity of P. xylostella reared on outdoor-grown cabbage cultivars varied ten-fold between the poorest and the best cultivar b ut plant age had little effect on P. xylostella reared on Chinese cabb age. In a glasshouse experiment, survival of P. xylostella on Chinese cabbage was significantly greater compared with field-grown glossy-lea ved, normal bloom green cabbage and red cabbage. In bioassays with neo nate larvae, when the leaves were placed vertically instead of horizon tally a significant level of intrinsic resistance was revealed for gla sshouse and field-grown glossy-leaved cabbage but not for Chinese cabb age. Observed differences in host status to P. xylostella are discusse d in relation to the potential for partial plant resistance in control programmes.