Tentiform leafminer typically attacks Populus (cottonwoods and aspens) and Salix (willows).  These small destructive pests (larvae of moths) feed on the interior leaf, which results in a transparent area that resembles a tent cover.  While they look back on the leaves, the damage is cosmetic. The leafminer has many natural enemies that feed on it.  Outbreaks are resolved in one to two years, usually without insecticides.