Parlatoria pergandii Comstock
Taxonomic placing: Insecta, Hemimetabola, Hemiptera, Sternorrhyncha, Coccomorpha, Coccoidea, Diaspididae.
Common name: Chaff scale.
Geographical distribution: Known from most regions where citrus is grown . In colder areas persists in greenhouses. CIE Map #185, 1964.
Host plants: In the Middle East, the chaff scale is common on citrus and also on Pistacia lentiscus L., Viburnum tinus L. and on Ruscus aculeatus L. World-wide this scale has been collected from about 80 plant species.
Morphology: The dorsal macroducts are two-barred. The orifices of the marginal macroducts on the pygidium are surrounded by strong sclerotized rings, and the body is oval. The chaff scale can be distinguished by lacking macroducts within the frame formed by the perivulvar pores (10-20 on each side); by the external margin of the similar pygidial lobes that are notched only once and by having its fourth lobe in the form of a conical projection. The anus is located close behind the posterior group of perivulvar pores. The prosoma bears 6-8 duct tubercles. The body of all stages (including the eggs and the winged males) is violet, except shortly after molting, when the body is white. The female shield is grey (chaff-like), about 1.2 to 1.7 mm in diameter, pear shaped. The dorsal exuviae of the younger stages are darker, sometimes with a yellowish tinge, located at one end of the female’s shield. The male shield is elongated, bearing at one end the darker shield of the crawler.
Life cycle: In the laboratory, reared on green lemons at 24-28°C and 70-80% RH, the scale completed a generation in 6-8 weeks, and females had about 75 progeny. The threshold of development was calculated to be 11°C and 715 days-degrees were required for one generation. Development was retarded and no eggs were produced at 32°C; low humidities hindered mating. In the coastal plain of Israel the pest raises four overlapping generations. Its populations on fruits and leaves peak in the spring and then decline rapidly, possibly due to the hot spring khmasin winds and to natural enemies, some of which are most active at that time. Scale numbers later increase, building up during summer and winter. The size of these populations appears to be stable from year to year. On the wooden parts of the trees very large numbers of ovipositing females are present the year around, suggesting that scales which later settle on fruit and leaves originate from these reservoirs. The plant organ that is infested, and the specific citrus variety, influence pest numbers and their size. Larger chaff scale populations occur on citrus fruit than on leaves, and the size of the insects is larger on the fruit. In addition, scales on grapefruits are about twice as big as those on oranges. In orchards where the pest coexists with the tropical grey chaff scale, Parlatoria cinerea; the latter dominates on leaves during winter, the chaff scale in the summer. As both pests are attacked by the same suite of natural enemies, these shifts probably reflect the scales’ sensitivity to prevalent humidities, with _P. cinerea _ being the more susceptible.
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. Most damage occurs on the fruits, whereon the scales settle shortly after fruit set, preferring the area under the sepals (“button”). The feeding sites remain undetected until the fruit begins to mature, due to the fact that these sites do not change color, remaining green. As a result many greenish, disfiguring blemishes appear on the yellow or orange-colored fruit, reducing their market value.
Green spots around the pests on alemon fruit
Y Drishpoun
Late-ripening citrus varieties, like Valencia, suffer heavier damage because the pest raises larger populations thereon. Damage is estimated to be below 10% of overall costs. Very heavy (but rare) feeding on leaves causes loss of color and twisting. The pest raises very 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 layers on the trunks and main branches. There is no indication that these layers cause any damage and the chaff scale does not secrete toxins into the host plants.
Management
Physical control: High-pressure water sprays (of 10-20 liter/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 white oils and/or organophosphates. A single application of an Insect growth regulator (IGR) currently suffices to control the pest for one year in Israel.
Biological control: The pest is attacked by several enemies. The most important predator is the coccinellid Chilocorus bipustulatus. Hemisarcoptes coccophagus is a major ectoparasitoid. Other enemies are the aphelinids Aphytis hispanicus and Encarsia inquirenda. 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. Parlatoria pergandii, and E. inquirenda may be mass-reared on Butternut squash fruit, Cucurbita moschata Duchesne.
References
Bar-Zakay, I. 1992. Using IGRs in citrus: achievements and problems. Phytoparasitica 20: 80.
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.
Gerson, U. 1967. Studies of the chaff scale on citrus in Israel. Journal of Economic Entomology 60: 1145-1151.
Gerson, U. 1967. Interrelationships of two scale insects on citrus. Ecology 48: 872-873.
Gerson, U. 1967. The natural enemies of the chaff scale, Parlatoria pergandii Comstock, in Israel. Entomophaga 12: 97-109.
Gerson, U. and Izraylevich, S. 1997. A review of host utilization by Hemisarcoptes (Acari: Hemisarcoptidae) parasitic on scale insects. Systematic and Applied Acarology 2: 33-42.
Gerson, U. and Y. Roessler. 1977. Distribution of chaff scales on citrus in Israel. Hassadeh 57: 864-865 (in Hebrew).
Moursi, K.S., Abdel Fattah, S., Rasha, Omar, M.A. and, Mourad, A.K. 2015. Population dynamics of chaff scale, Parlatoria pergandii Comstock, in comparative analysis of fluctuating population densities on three citrus varieties in El-Beheira Governorate, Egypt. Communications in Agricutural and Applied Biological Science 80: 71-8.