The armored scale insects Chionaspis pinifoliae (Fitch) and Chionaspis heterophyllae Cooley (Hemiptera: Diaspididae) overlap broadly in host range and geographic distribution and are so similar in morphology that they can be distinguished only by a subtle morphological character of the adult females: the form of the median pygidial lobes. However, this character is quite variable for both species. We used allozyme electrophoresis and DNA sequencing of a region that included the mitochondrial genes COI and COII to determine whether two species really exist and, if so, whether the morphology of the pygidial lobes is a reliable character to use to discriminate between them. Material for genetic analysis was collected as third instar females from five Illinois populations of each species (as identified by morphology of the pygidial lobes). Chionaspis species were difficult to analyze electrophoretically, but fixed allelic differences were found at three allozyme loci: malic acid dehydrogenase (Mdh), phosphoglucose isomerase (Pgi), and an esterase (Est). The 572-bp (alignment length) mitochondrial region was invariant within species but differed between the species for both base substitutions (p-distance = 0.091) and insertion-deletion differences. Estimated divergence time was at least 3.8 million yr. The consistent absence of heterozygotes at the three allozyme loci and the large mitochondrial sequence difference confirms that the morphology of the pygidial lobes is a reliable and convenient character for identifying C. pinifoliae and C. heterophyllae and supports the hypothesis that they are not only separate, but very old species.