Chromatomyia horticola (Diptera
Agromyzidae) were reared from the collected leaves. This leafminer was found infesting 11 vegetable species at Gia Lam, Hanoi. C. horticola commonly infests tomato, cumcuber and garland chrysanthemum, being most abundant in spring and winter cropping season. The density of and the rate of damage by C. horticola were lowest in late winter season, but there was no significant difference between main and early season. Previous crops affect the density of C. horticola on curcumber. The density C. horticola was also lowest in the field that plants were not found hosts as wax gourd. The density of the leafminer in crossed curcumber higher than in local curcumber.