VARIATION IN PERFORMANCE OF WESTERN FLOWER THRIPS POPULATIONS ON A SUSCEPTIBLE AND A PARTIALLY RESISTANT CHRYSANTHEMUM CULTIVAR

Variation in host plant performance among populations of a phytophagou s insect pest is a potential threat to the durability of host plant re sistance. Aggressive biotypes may overcome the protective properties o f formerly resistant cultivars. Therefore, it is of interest to study such variation in breeding programs for host plant resistance to insec ts. In the present study, the performance of ten populations of Frankl iniella occidentalis, the western flower thrips, was determined on a s usceptible and a partially resistant cultivar of chrysanthemum, Dendra nthema grandiflora. Damage, reproduction, and adult survival were dete rmined using an excised leaf assay. Significant differences between th e two cultivars and among the ten populations were found for all three characteristics. In general, damage, reproduction and adult survival were reduced on the resistant cultivar when compared to the susceptibl e cultivar. Some populations showed, in comparison to the reference po pulation from the Netherlands, much higher damage and reproduction on one or both chrysanthemum cultivars. But also in these populations per formance on the resistant cultivar was poor compared to the susceptibl e cultivar.