Field of sclerotized scales on either the first abdominal tergite (Agromyza:Ag intermittens strid file.pct) or just below (most Liriomyza: e.g. Li trifolii strid.pct, Li trifolii strid2.pct, Li trifolii strid3.pct). It is operating as part of the stridulation mechanism of some agromyzids (for more details see the section on External adult morphology).

Alternative form for stridulatory file : file.