Predators mediate host plant resistance to a phytophagous pest in cabbage with glossy leaf wax

Abstract

This study examined the role of generalist predators in producing higher mortality of Plutella xylostella L. (Plutellidae) larvae on glossy vs. normal‐wax cabbage, Brassica oleracea var. capitata L. To test this, survival and feeding of P. xylostella were measured on individually caged glossy and normal‐wax plants with and without each of three generalist predators, Chrysoperla carnea (Stephens) (Chrysopidae), Orius insidiosus (Say) (Anthocoridae), and Hippodamia convergens Guerin‐Meneville (Coccinellidae). In the greenhouse, predators always significantly reduced survival of P. xylostella larvae on glossy plants, but never on normal‐wax plants. In the field, predators significantly reduced P. xylostella survival on glossy plants, but only C. carnea was effective on normal‐wax plants. In similar experiments with excised leaves, O. insidiosus and C. carnea were more effective predators on the glossy leaves, while H. convergens was equally effective on both kinds of leaves. Patterns for feeding were similar, but significance levels differed from those for P. xylostella survival. The greater effectiveness of predators on glossy plants is apparently due to the reported improved mobility of these animals on glossy leaf surfaces. The data also suggest that reduced mining by P. xylostella exposes the larvae to more predation on glossy plants and contributes some to the resistance. Regardless of the mechanism, resistance to P. xylostella on glossy B. oleracea appears to depend on the action of generalist predators for its full expression. This dependence on predation must be considered in the development and deployment of glossy insect‐resistant B. oleracea. 1995 The Netherlands Entomological Society