Lepidosaphes ulmi (L.)
Common name: Oystershell scale.
Geographical distribution: Cosmopolitan, occurring in all apple-growing regions. CIE Map #49, 1982 (revised).
Host plants: The oystershell scale was collected from over 130 host plants, but is most prevalent on apples. In Israel it was also collected from carobs, grapevines, walnut, white poplar and other perennials.
Morphology: The two-barred dorsal macroducts are arranged in transverse rows, the six pairs on the pygidium’s margin being extra large. The median pair of lobes are rounded, separated; the second pair are bi-lobed, the third pair occur only as lightly-sclerotized protrusions. The anterior abdominal segments bear hyaline spurs, and as well as single, sclerotized, strong spurs between the segments. The perivulvar pores are arranged in five clusters, about 25-50 in two groups on either side of the anus. The fifth group, of about 15-20 pores, is situated just below the anus. The male is winged, white-yellow in color. The pale-yellow body of the female is elongated, narrowing anteriorly and its shield is purple-brown, elongated or twisted, dependent on the colony’s density, up to 3.5 mm in length, with the darker juvenile dorsal exuviae placed at the narrow end. The shield of the male (if present) is slightly darker, with the 1st-stage dorsal exuvium at its apex.
Life cycle: The pest infests mainly trunks, branches and fruit, rarely the leaves. In the Middle East it raises 1-2 annual generations and each female lays 50-100 eggs. The oystershell scale occurs in several races or strains on different host plants and regions. They may reproduce sexually or by parthenogenesis (being uniparental); such races were even given separate subspecific status. They may be univoltine, bivoltine and even polyvoltine, and may, or may not, infest the same host plant, differ in fecundity and cold-hardiness, as well as possess, or lack, an embryonic diapause. Taken together, these data suggest that several species may be masquerading under the label Lepidosaphes ulmi.
Economic importance: The oystershell scale is a major pest of apple in North America, Europe and Australasia, but in the Middle East it sometimes injures grapevines. Its crawlers settle on trunks, branches and fruit, forming heavy encrustations and even splitting the former, disfiguring the latter. Damage is mainly due to sucking the host plant’s sap, but the injection of toxins may contribute to the injury. Heavy infestations result in stunted tree growth and reduced fruit quantity and quality.
Biological control: In the Middle East this scale is sometimes attacked by the [ectoparasitoid]
Erler, F. and Tunç, I. 2001. A survey (1992-1996) of natural enemies of Diaspididae species in Antalya, Turkey. Phytoparasitica 29: 200-305.
Gerson, U. 1990. Biosystematics. In: Rosen, D. (Ed.) 1990. Armored Scale Insects; Their Biology, Natural Enemies and Control, Volume 4A, pp. 129-134, Elsevier, Amsterdam.
Gharib, B. and Bénassy, C. 1983. Étude éco-hysiologique des arrets de développement de la cochenille Lepidosaphes ulmi L. (Coccoidea, Diaspididae). II. Conditions de reprise du développment embryonnaire des deux races du pommier et du peuplier. Acta Oecologica 4: 185-193.
Katsoyannos, P. and Stathas, G.J. 1995. Phenology, embryonic diapause and importance of natural enemies of Lepidosaphes ulmi L.) (Homoptera: Diaspididae) on olive trees in Greece. Israel Journal of Entomology 29: 199-206.