Ann. zyxwvutsrqponm appl. Biol. zyxwvutsrqp (1994), zyxwvuts 125, 477-488 Printed zyxwvutsrq in Great Britain 477 zy Interactions between the diamondback moth, zyx Plutella xylostella L. and glasshouse and outdoor-grown cabbage cultivars By R H J VERKERK and D J WRIGHT Department of Biology, Imperial College at Silwood Park, Ascot, Berks SL5 7PY, UK (Accepted 29 July 1994) Summary Interactions between Brassica cultivars (cvs) and adult and larval stages of Plutella xylostella L. were examined. In six-way choice oviposition experiments, glasshouse-grown Chinese cabbage cv. Tip Top was preferred to five outdoor- grown temperate cabbage cultivars but was similar to four out of five tropical cultivars. Bionomic studies with neonate larvae on temperate cabbage cultivars showed that mean larval duration was longer and percentage survival less on older compared with younger 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 but plant age had little effect on P. xylostella reared on Chinese cabbage. In a glasshouse experiment, survival of P. xylostella on Chinese cabbage was significantly greater compared with field-grown glossy-leaved, normal bloom green cabbage and red cabbage. In bioassays with neonate larvae, when the leaves were placed vertically instead of horizontally a significant level of intrinsic resistance was revealed for glasshouse and field-grown glossy-leaved cabbage but not for Chinese cabbage. Observed differences in host status to P. xylostella are discussed in relation to the potential for partial plant resistance in control programmes. Key words: Insect, oviposition, bionomics, plant resistance, ditrophic Introduction Plutella xylostella L. is a major and widely distributed oligophagous pest of crucifer crops. It causes the most serious economic losses in tropical vegetable-growing regions owing to short generation times, high fecundity, sub-optimal biological control and an almost unparalleled tendency for development of insecticide resistance in the field (Talekar zy & Griggs, 1986; Talekar, 1992). Intrinsic host-plant resistance, mediated through such mechanisms as toxins, digestibility reducers, trichomes, tissue hardness and leaf waxiness (van Emden & Way, 1972), has yet to have been shown to be effective as a unilateral control strategy (Talekar & Griggs, 1986; Talekar, 1992). A limited exception is the recent development of glossy-leaved cabbage genotypes (Dickson et al., 1990; Eigenbrode & Shelton, 1992). Quantification of key bionomic aspects of the P. xylostella host-plant interaction, the principal aim of the present work, is critical as a base-line for evaluation of the possible role of extrinsic resistance (Price, 1986), where plants benefit from the natural or applied enemies of herbivores. zy 0 1994 Association of Applied Biologists