A root maggot that damaged lettuce was observed at many lettuce production bases in Beijing in recent years,which was a serious threat to lettuce production.The damage by lettuce root maggot was investigated in lettuce field and the species of the root maggot was identified by mitochondrial cytochrome oxidase Ⅰ(mt COⅠ)molecular marker and morphological characteristics of the adult.The results showed that root maggot damaged lettuce root-stem and caused lettuce plants to die or stop growing during seedling s...