Chrysomphalus aonidum (L.)
(Formerly known as Chrysomphalus ficus Ashmead)
Common name: Florida red scale, circular black scale; circular purple scale, Egyptian black scale.
Geographical distribution: Outdoors in most tropical and subtropical regions of the world; in cooler areas within greenhouses. Distribution Maps of Plant Pests, Map 4, June 1988.
Morphology: The body of the female is yellow, pear-shaped, the pygidium with three large lobes, all with an external notch, the fourth lobe a small rounded projection. The dorsal macroducts are one-barred, slender. A group of three long macroducts, beginning near the vulva, open just outside the median lobes. Five club-like processes (paraphyses) arise from the lobes on either side of the pygidium. The anus is located just above the median paraphyses. The vulva is surrounded by about 10 perivulvar pores on either side, plus a small cluster of pores in front. A distinct spur is located on the margin of the thorax, across from the posterior spiracles. The shield is purple-black, round and flat, about 2.0-2.3 mm in diameter, the dark-red juvenile exuviae are slightly off-center. The winged males are pale-orange, their dark shields oval, the exuvium of the 1st instar placed near one end.
Life cycle: Florida red scale annually raises four generations, the peaks in crawler production occurring in February, June, September and October. Pest populations have two yearly peaks; they attain their largest numbers in the autumn, drop during winter, and increase in mid-summer to decline again in late summer and then peak. The crawlers are very sensitive to the dry and hot spring khamsin winds, and prefer to settle in the inner parts of trees, usually not far from their mothers. The threshold for development was calculated to be at 11°C and 825 days-degrees are required for one generation. The optimal conditions for development seem to be 24°C and air humidity of above 60%. The fecundity of the scale is affected by the season and by the host plant. An average of 224 offspring was produced on lemon fruits in the spring, 108 in summer and only 40 on the same host in the autumn. On citrus leaves only 20 crawlers were produced in the spring, 80 in summer and 44 in autumn. The pest may be mass-reared on banana squash fruit. However, heavily-infested fruits do not last long, probably due to toxins injected into these hosts.
Economic importance: The pest occurs on the leaves and fruit of citrus, rarely on branches. Although attacking young as well as on established citrus trees, it prefers the latter. During feeding the scale secretes toxins into the infested leaves, which then turn yellow and drop. Heavy leaf drop may retard and stunt tree growth, affecting the yield. Young infested fruits shrink and fail to develop, if attacked at a later stage, the black, hard-to-remove shields cover the face of the fruit, reducing its market value. Generally the scale prefers grapefruits and oranges over lemons, and may at times also damage banana. In the past this scale was one of the major pests of citrus in Israel, but following its complete biological control along the coastal plain, it ceased to be of economic importance.
Mechanical control: The pests may be removed from infested fruit in packing houses by applying high-pressure water sprays descaling machines, which dislodge the scales.
Chemical control: The pest can be controlled with white oil applied when its populations ebb, in late summer, or (on Valencia) in autumn. If windbreak trees (e.g. cypress) are also infested, they should likewise be sprayed.
Biological control: The aphelinid ectoparasitoid Aphytis holoxanthus DeBach and the endoparasitoid Pteroptrix smithi (Compere) were introduced into Israel in 1956. Together they provide complete control of the pest, unless disrupted by pesticides. The coccinelid Chilocorus bipustulatus is an important predator.
Drishpoun, Y. 2000. A Guide to the Control of Citrus Pests. Ministry of Agriculture and Rural Development, Extension Service, pp. 97 (in Hebrew).
Rosen, D. 1965. The hymenopterous parasites of citrus armored scales in Israel (Hymenoptera: Chalcidoidea). Annals of the Entomological Society of America 58: 388-396.
Shahein, A. El-Kholy, A.S. Moussa, S.F.M. Helmy, E.I. Selim, A.A.1994. Population dynamics of the Egyptian black scale insect Chrysomphalus aonidum L. on balady navel and sweet organes with reference to the biotic and abiotic factors
Steinberg, S., Podoler, H. and Rosen, D. 1986. Biological control of the Florida red scale, Chrysomphalus aonidum, in Israel by two parasite species: current status in the coastal plain. Phytoparasitica 14: 199-204.