Larvae of Phyllocnistis unipunctella (Stephens) mining the upperside and underside of leaves of Populus spp. were compared in terms of gross morphology and the COI DNA barcoding section of mitochondrial DNA. It was discovered that larvae feeding on the underside did not show the dark pigmentation of the prothoracic plate as described in the literature. Larvae were found feeding two months earlier than normal and at least one extra generation was observed. More work is required to determine the possibility of speciation.