COMPARISON OF SUSCEPTIBILITY OF DENDRANTHEMA-GRANDIFLORA (TZVEL) CULTIVARS TO LEAFMINER, LIRIOMYZA-TRIFOLII (BURGESS) (DIPTERA, AGROMYZIDAE)

Dendranthema grandiflora (TzveL.) (84 cultivars) grown under conventional pest control was examined for damage by Liriomyza trifolii (BURGESS) during the flowering period. All cultivars had punctures and mines. SP1332, Pierrot and three other cultivars had only small inconspicuous mines less than 0.5 mm in width, and damage was negligible. Sixteen cultivars, including MonBlanc and Waltz had many (>50% of leaf area) large mines (>1 mm in width) on all leaves from the bottom to top of the stem. The other 63 cultivars fell into three categories between the above two types. The number of large and medium mines per unit leaf area increased significantly (p<0.01) with the extent of damage. However, the number of punctures per unit leaf area showed no significant difference between categories. The percentage of punctured or mined leaves per stem also showed no significant difference. Flowering occurred earlier in more damaged cultivars than in less damaged ones (p<0.01), but this parameter was no indicator of resistance due to considerable variation.