Lepidosaphes beckii (Newman)
Taxonomic placing: Insecta, Hemimetabola, Hemiptera, Sternorrhyncha, Coccomorpha Coccoidea, Diaspididae.
Common name: Purple scale; citrus mussel scale
Geographical distribution: Apparently wherever citrus is grown; in the Middle East (Cyprus, Israel, Turkey) since the beginning of the 20th century. In Israel it infests citrus only along the coastal plain.
Host plants: In the Middle East, mostly on citrus.
Morphology: The dorsal macroducts are two-barred, the six pairs on the margin of the pygidium are extra large. The pale-yellow body of the female is elongated, narrowing anteriorly. The median lobes are triangular, clearly separated; the second pair of lobes are bi-lobed, the third pair occur as lightly-sclerotized protrusions. The anterior abdominal segments are clearly lobed, projecting laterally, with strong spurs. The dorsal ducts are arranged in transverse rows. Perivulvar pores in five clusters, about 20-30, in two groups on either side of the anus. The fifth cluster, of about 6-10 pores, is situated above the anus. The male is winged, white-yellow in color. The shield of the female is elongated up to 3.5 mm in length, narrowing anteriorly, slightly curved, purple-brown, with the paler juvenile dorsal exuviae placed at the narrow end. The whitish ventral exuvium (“velum”) is retained, located below the body of the scale. The shield of the male is slightly darker, with the 1st-stage dorsal exuvium at apex.
Life cycle: The purple scale infests mostly leaves and fruit, is less common on green twigs (which it may kill), and seldom occurs on wooden branches. It prefers the inner parts of trees and usually begins to be noticed in citrus orchards as they reach their 10-12th year. When pest crawlers settle on young fruit in the spring they prefer the underside of the calyx, may thus remain unnoticed at first. Later they colonize the upper parts of the fruits and then the entire face. Scales on fruit produce about 250-300 eggs per female, those on the leaves only about 170. The threshold of development is at 8°C and about 1,100 day-degrees are required for completing one generation. In Israel the pest raises four annual generations. Purple scale may be mass-reared on green lemons, potatoes and banana squash.
Economic importance: Purple scale may be a major pest of citrus, attacking the leaves and fruit. Heavily infested leaves turn yellow, probably from a combination of losing assimilates and a toxic secretion, and may drop. As a result tree growth is stunted. The sites where the fruit-infesting scales had fed remain green at color change, detracting from their market value.
Management
Chemical control: If necessary, the pest may be controlled with white oils and/or organophosphates.
Biological control: Purple scale is completely controlled in the Middle East by the introduced aphelinid ectoparasitoid Aphytis lepidosaphes Compere, which is attracted to the purple scale by a kairomone. In Greece substantial reductions in pest numbers were attributed to the parasitic mite Hemisarcoptes sp. (Hemisarcoptidae).
References
Abdel-Fattah, M.I. and El-Saadany, G. 1979. The role of parasitoids in the control of the purple scale, Lepidosaphes beckii (New.) in Egypt. Zeitschrift für Angewandte Entomologie 87: 154-159.
El-Kareim, A.I.A. and Shanab, L.M. 1992. Host-seeking stimulants (kairomones) for parasitoids of purple scale insects. Acta Phytopathologica et Entomologica Hungarica 27: 29-34.
Rosen, D. 1965. The hymenopterous parasites of citrus armored scales in Israel (Hymenoptera: Chalcidoidea). Annals of the Entomological Society of America 58: 388-396.