Shape and coloration highly variable depending on host plant and age of the scale. Body usually oval or round. Dead females are leathery brown and vary in profile from slightly convex to pyramidal or hemispherical. Ebeling (1938) published an excellent study on the effects of host plants on the shape of this scale. Coloration of living stages varies with the time of the year and part of the plant infested. Stages on the leaves are usually semitransparent yellow-green; stages on twigs are mottled yellow and brown. Eggs are laid under the body of the female and there is no ovisac. Occurring on arboreal parts of plant. Males are present but are uncommon; the species is thought to be parthenogenetic.
Parthenolecanium corni is similar to P. fletcheri (Cockerell) and P. quercifex (Fitch) but differs from the former by having dorsaltubular ducts (normally lacking in P. fletcheri) and differs from the latter by usually having submarginal tubercles (normally lacking in P. quercifex).
U.S. quarantine notes
This species was intercepted 15 times at U. S. ports-of-entry between 1995 and 2012, with specimens originating from China, Czech Republic, France, Germany, Mexico, The Netherlands and The United Kingdom of Great Britain, and N. Ireland. We also have examined specimens taken in quarantine from Britain (Cornus, Cotoneaster, Escallonia, Fragaria, Gaultheria, Prunus, Rhododendron, Ribes, Robinia, Rosa, Sarcococca, Veronica); Canada (Acer, Cornus); Chile (Vitis); Czechoslovakia (Malus, Prunus, Tilia); Denmark (Ribes, Salix); France (Laurus, Prunus, Ribes, Rubus, Vitis); Germany (Acer, Aesculus, Alnus, Celtis, Fraxinus, Ligustrum, Lonicera, Malus, Philadelphus, Prunus, Robinia, Ribes, Sorbus); Greece (Rosa); Italy (Crataegus, Laurus, Rosmarinus); Japan (Diospyros, Prunus, Wisteria); Mexico (Condalia); The Netherlands (Buxus, Caragana, Cornus, Corylus, Crataegus, Magnolia, Rhododendron, Robinia, Spiraea, Viburnum); Norway (Sorbus); Poland (Alnus, Juglans, Ribes); Sweden (Crataegus, Ribes); Switzerland (Prunus); Yugoslavia (Rosa). It is most commonly collected on a wide variety of deciduous hosts, especially fruit trees in the genus Prunus. ScaleNet includes hosts on over 50 plant families from 45+ countries worldwide. It is widespread in the Nearctic and Palaearctic regions and does not occur in the Afrotropical region. One other species of Parthenolecanium has been taken at U. S. ports-of-entry, but not recently. Parthenolecanium persicae (Fabricius) has been intercepted from Australia, Chile, England, France, Italy, Japan and New Zealand.