Behavior of Neonate Diamondback Moth Larvae (Lepidoptera: Plutellidae) on Glossy-Leafed Resistant Brassica oleracea L.

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Abstract
The dispersal and survival of neonate diamondback moth larvae, Plutella xylostella (L.), were measured on normal bloom susceptible ‘Round-Up’ cabbage and a resistant genotype descended from glossy cauliflower, PI 234599. During the first 24 h after hatching, neonate P. xylostella dispersed more rapidly and initiated fewer mines on the resistant glossy 2518 than on ‘Round-Up’. Also, a greater proportion of neonates were found dead on 2518 than on ‘Round-Up’. Individual neonates had significantly higher movement rates on three glossy resistant genotypes of Brassica oleracea than on two normal bloom types. Movement rates were negatively correlated with percentage of larvae surviving to fourth instar. Removal of leaf epicuticular waxes with dichloromethane or disruption of the wax morphology eliminated the difference in movement rate on ‘Round-Up’ and 8329, a glossy cabbage descended from PI 234599. Headspace vapor of 8329 or ‘Round-Up’ plants did not affect movement rates of neonate P. xylostella. The results indicate that wax morphology is of primary importance in producing increased larval movement rates on glossy resistant lines. Wax chemistry may also contribute to the effect. Neonate nonpreference for leaf wax characteristics is proposed as the mechanism of resistance to P. xylastella in glossy B. oleracea.