Cross-resistance of chrysanthemum to western flower thrips, celery leafminer, and two-spotted spider mite

Chrysanthemum [ChrysanthemumxmorifoliumRamat. (Asteraceae)] is one of the economically most important greenhouse ornamentals worldwide. A major constraint in chrysanthemum production is adequate pest management, requiring the use of different tactics, such as improving host plant resistance, in the framework of an integrated pest management (IPM) approach. In this study, we investigated cross-resistance of chrysanthemum to its three major pests: western flower thrips [Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae)], celery leafminer [Liriomyza trifolii (Burgess) (Diptera: Agromyzidae)], and two-spotted spider mite [Tetranychus urticaeKoch (Acari: Tetranychidae)]. We quantified resistance to each pest by performing greenhouse bioassays with a broad range of chrysanthemum types from commercial germplasm provided by Dutch breeding companies. Considerable variation was detected among the chrysanthemum cultivars in thrips silver damage and growth damage, leafminer damage, measured as number of mines and pupae, and spider mite numbers and damage. We observed significant positive correlations between thrips damage (both silver and growth damage) vs. leafminer numbers (both mines and pupae), and between leafminer numbers (both mines and pupae) vs. spider mite numbers. Our results indicate an overlap in resistance to all three herbivores. The important implications of this result for chrysanthemum breeding are discussed.