Icerya purchasi (cottony cushion scale)

Sap depletion may lead to wilting, leaf drop, dieback, and stunted growth. As with most sap-sucking insects, the production of honeydew leads to the growth of sooty mould.

Damage to the plant by I. purchasi is mostly caused by sap depletion; the shoots dry up and die, and defoliation occurs. In addition, the copious quantities of honeydew produced by the scales coat the leaves, blocking the stomata and impeding gas exchange. Such fouling frequently results in the growth of sooty moulds over the leaf surfaces, which blocks light from the mesophyll, so reducing photosynthesis.I. purchasi is a particular pest of citrus, Acacia spp., Casuarina spp. and Pittosporum spp., but it can damage many types of fruit and forest trees, and ornamental shrubs and trees. After its introduction into California, USA, in the late nineteenth century, it was recorded devastating citrus orchards, killing even large trees. By 1887, the problem on citrus had increased to such serious proportions that the entire citrus industry of California was threatened with destruction (Bartlett, 1978). Serious damage to citrus orchards by I. purchasi was also recorded in many other countries when the cottony cushion scale first arrived (Williams and Watson, 1990), but with successful biological control this insect has become relatively unimportant in fruit orchards today.In Anhui, China, I. purchasi is one of the most important pests of pomegranates (Punica granatum) (Wang et al., 2002), and in Zhejiang, China, the cottony cushion scale is the main pest damaging Liquidambar formosana (Formosan-gum) (Hua et al., 1999). In Israel, the cottony cushion scale was a serious pest in the northern part of the country until biological control became established, which reduced it to minor pest status (Ben-Dov, 1995).