Coccoidea

Insect superfamily that includes scale insects and mealy bugs. This is an unusual group in that its members do not resemble ordinary insects, but look more like inanimate particles. In general they are small and inconspicuous, ranging on the average from 1–15 mm/0.039–0.58 in, although some of the larger forms attain 30 mm/1.2 in.

About 4,000 species have been recorded; they abound in tropical countries, and in temperate countries they are glasshouse pests, and pests of fruit trees and shrubs. They exhibit a range of developmental patterns, with production of a neotenous (degenerate) female form. The females do not have wings, and are to a great extent immobile; they cling to the stems and leaves (sometimes roots) of plants and trees by means of their mouthparts. When males are present they are winged and do not feed. The males are short-lived and participate only in reproduction, in species that reproduce sexually. Some species may reproduce asexually, by parthenogenesis.

Classification Coccoidea is in the suborder Homoptera of order Hemiptera class Insecta, phylum Arthropoda.

The wings in the male consist of a single pair of forewings bearing slight venation (arrangement of veins). The hindwings are reduced to knoblike stalks, which are attached to the fore pair by means of a threadlike structure.

The classification of Coccoidea is controversial, but there are about 15 families, falling broadly into three groups: the mealy bugs; the soft scales; and the armoured scales. The mealy bugs are the least degenerate Coccoidea; the adult female has legs and antennae and moves about sluggishly. They are covered with a powdery waxlike secretion which may extend beyond the body as threads or filaments. The eggs are laid in an egg sac made up of waxy filaments secreted by the female. Mealy bugs are insect pests of fruit trees in the tropics and also attack glasshouse crops: they feed on the plant sap and excrete honeydew in which a mould grows.

Soft scales are generally larger than the mealy bugs and the bodies of the nymphs are soft. The adult females, in contrast, have a hard dorsal exoskeleton. The nymphal stage represents the active wandering phase, and the nymph possesses legs and antennae. The adult female's legs are much reduced and it develops into a flattened scalelike creature that clings firmly to the plant. When males are present they are winged. The female lays her eggs under her body and often secretes wax to form an egg sac. She then dies, and the dorsal part of her body remains attached to the egg sac in the form of a protective scale. Like the mealy bugs, the soft scales excrete honeydew. In general, they are brown, hemispherical and measure 3–5 mm/0.1–0.2 in length.

Armoured scales include members of the family Diaspididae. They are the most important scale insects both for the damage they do to plants and trees, and because of their specialization. They may take on varied forms: circular, elongate or threadlike scales. They are active during the nymphal stage. The anterior region is covered by a hard, protective scale; the posterior part of the abdomen forms the pygidium (terminal segment). After the first moult the legs are lost and the antennae are reduced in size. Adult females are inactive, produce eggs and eventually die. The most famous representative of armoured scales is the San Jose scale Aspidiotus perniciosus, which is a serious pest of fruit trees in California, USA. It attacks peaches, plums, apples, pears, and apricots. Another interesting representative is the mussel scale, Lepidosaphes ulmi.