Parlatoria cinerea Hadden
Taxonomic placing: Insecta, Hemimetabola, Hemiptera, Sternorrhyncha, Coccomorpha, Coccoidea, Diaspididae.
Common name: Tropical grey chaff scale.
Geographical distribution: This is a circum-tropical species. In Israel it is more common in the inner parts of the country, where it still seems to be spreading.
Plant hosts: All varieties and species of citrus, mango (only in Jamaica) and various ornamentals.
Morphology: The dorsal macroducts are two-barred. Like in other species of Parlatoria, the orifices of the marginal macroducts on the pygidium are surrounded by strong sclerotized rings, and the body is oval. This scale can be distinguished by having 3-4 macroducts within the frame formed by the perivulvar pores, of which there are about 20-25 on each side, by the twice-notched external margin of its lobes, and by the fourth pygidial lobe which resembles a broad rounded protrusion. The anus is located between the posterior pores of the caudal group of perivulvar pores. The prosoma bears 6-8 duct tubercles. The body of all stages (including the winged males) and of eggs is violet, except shortly after molting, when it is white. The shield of the female is grey, oval, pear shaped. The dorsal exuviae of the younger stages are darker, placed at one end of the female’s shield. The shield of the male is elongated, slightly curved, bearing at one end the darker exuvium of the 1st-instar nymph.
Life cycle: The biology of this pest has not been studied, but it is probably similar to that of the chaff scale,
Parlatoria pergandii Comstock,
except that P. cinerea seems to prefer warmer and more humid climates. In orchards where it coexists with the chaff scale, the latter dominates the leaves during summer, tropical grey chaff scale in the winter. As both pests are attacked by the same suite of natural enemies, these shifts probably reflect the scales’ sensitivity to prevalent humidities.
Economic importance: The pest infests all above-ground parts of citrus trees aged 10-12 years or more; heavy attacks on such trees may retard their development. In South America it also infests citrus roots. Most damage occurs on the fruit, which is infested by the scales shortly after setting; the wounds they inflict remain undetected until the fruit begins to change its color. The site around the wound remains green, resulting in many greenish, disfiguring blemishes, which reduce the fruits’ market value. Late-ripening citrus varieties, like Valencia, suffer heavier damage because the pest has had more time to raise larger populations thereon. Damage is estimated to be below 10% overall costs. Very heavy feeding on leaves may cause foliage twisting. The pest raises large populations on the woody parts of citrus trees (especially on the trunk), and as the dead insects do not drop off, this results in thick encrustations on the trunks and main branches. There is no indication that these encrustations cause any damage and P. cinerea does not secrete toxins into the host plants.
Management:
Physical control: High-pressure water sprays (of 10-20 litre/tree at 300 psi) may reduce scale populations on the trunk and main branches by over 60% within three months, by about 90% after one year.
Chemical control: The pest can be controlled by mineral oils and/or organophosphates. An application of an insect growth regulator (IGR) often suffices to control the pest for one year.
Biological control: The pest is attacked by several enemies. The most important predator is the coccinellid Chilocorus bipustulatus (L.). The mite Hemisarcoptes coccophagus Meyer (Hemisarcoptidae) is a major ectoparasitoid, as is Aphytis hispanicus (Mercet) (Aphelinidae). Another important aphelinid is the endoparasitoid Encarsia inquirenda (Silvestri). The predators are most active on the wooden parts of the trees during summer, whereas the parasitoids attack the pest mostly in the spring, especially on the leaves and fruits. Neither group of natural enemies appears to reduce the level of pest damage, but the predators, acting during summer, when the pest increases its populations, appear to be more important in reducing scale numbers.
References
Cesnik, R. and Medina, C.L. 1995. High pressure water sprays to control chaff scale (Homoptera: Diaspididae) in citrus. Journal of Entomological Science 30: 93-94.
Da Fonseca, J.P. 1965. Uma cochonilha de escama recentemente observada em laranjais de Sao Paulo. O Biologico 31: 216-219.
Gerson, U. 1964. Parlatoria cinerea, a pest of citrus in Israel. FAO Plant Protection Bulletin 12: 82-85.
Gerson, U. 1967. Interrelationships of two scale insects on citrus. Ecology 48: 872-873.
Gerson, U. and Roessler, Y. 1977. Distribution of chaff scales on citrus in Israel. _ Hassadeh_ 57: 864-865 (in Hebrew with English abstract).