White Wax Scale (Cascardia Destructor)

White wax scale (Cascardia destructor)

Introduction: White wax scale is a pest of subtropical and temperate climates with relatively high humidity in summer. It is killed by high temperatures in summer. It thrives best on vigorous trees, where it produces the largest individuals and, subsequently, the greatest numbers of eggs.

Host plants: White wax scale has a very wide host range among both native and introduced plants, including ornamentals and weeds. All citrus varieties, grapefruit, guava, persimmon, mango, pear, and quince. Gardenia, lillypilly, pittosporum, and blackthorn, Bursaria spinosum, are also common hosts.

Description: The adult female is enveloped in soft white wax, and may be about 10 mm. long and 7 mm high, although many are only half that size. The chemical composition of the wax has been examined by Hackman (1951). The body of the insect beneath the wax is light red to dark brown, plump and soft. Its hind end narrows into the caudal process that lies flat on the leaf or twig. The Indian white wax scale, Ceroplastes cerifrus, has an elevated caudal process, and the insects's wax coverign has a short down- turned horn at one end.

Life cycle: Egg development occurs during late winter, and egg-laying beneath the body of the insect begins in spring. As the eggs are laid the body shrinks upwards until its ventral surface is close to the dorsal surface, the insect is dead, and all the space beneath it is packed with the oval salmon-colored eggs- up to 3000 in number. The larvae hatch from the eggs, and leave the space beneath the dead parent scale filled with the white remains of the hatched eggs. The larvae are light brown, oval, six-legged and about 0.5 mm long. They make their way towards the outside of the tree and settle, usually on a leaf but sometimes on a young green twig, and commence feeding. Probably, because of their attraction to light, they tend to be on the upper surfaces of the leaves of range, lemon and grapefruit, but on both surfaces of mandarin leaves which are more upright and therefore well lit on both sides. The larvae settle beside the midrib, or if that is crowded, beside a lesser vein. In heavy infestations they settle in two rows - one on each side of the midrib - and there may be as many as 200 larvae per leaf. Within a few hors of steeling the larvae produce white marginal rays of felted material - four at each side, three in front and four at the rear - and a white felted pad on the dorsal surface. They remain on the leaf for four to five weeks, then move to the twigs and settle on permanent positions, usually on new or year-old wood. Feeding starts again and white wax production commences. A conical cap of wax is soon formed and the insect is at the 'peak' stage, which is followed a few weeks later by the 'dome' stage. The wax increases until the scale is fully developed by April. The insect beneath the wax is an adult at the peak stage.

Injury: Direct injury from the feeding seems negligible, but both larvae and adults produce honeydew, which cause problem of black sooty mould fungi on leaves and fruits. The sooty mould can retard color development of the new fruit and interfere with photosynthesis. However, no measurable effects have been observed.