White-flies, or mealy-wings, are minute sap-sucking insects, having the body and wings covered with mealy wax. The female (Fig. 8, P) lays her eggs, frequently in circular batches, upon foliage, and the young insects (N) are active, but settle down and commence feeding soon after hatching. Later the insects change to another form (O), without legs and antennæ, and so resemble scale insects to a certain extent; from the latter, however, they may be distinguished by the waxy covering, bearing spine-like processes, and by being surrounded by a distinct marginal area. An important species in New Zealand is the greenhouse white-fly (_Trialeurodes vaporariorum_), against which fumigation with calcium cyanide is the best as a check. Thrips. The foliage of many plants is sometimes infested by very minute black insects, known as thrips. A species commonly met with is that found upon ripe peaches. Thrips are readily identified by the structure of the wings (Fig. 8, 4), which are but narrow strips fringed with long, rigid hairs. These insects, by puncturing the plant tissues and sucking up the nutrient sap, very often are responsible for infecting healthy plants with disease, such as mosaic. According to the species of thrips, the female lays her eggs either in the plant tissues or upon the surface. The young insects are wingless, but attack the plant in the same manner as does the adult; as development proceeds, the insect transforms to a pupa, from which the adult ultimately emerges. A characteristic symptom of thrips infestation is a silvering of the foliage, while the leaves are further rendered unsightly by the minute specks of hardened excreta ejected by the insects. Many thrips pass their whole development upon the host plants, while others pass part of their lives underground. One of the commonest species met with under glass and out of doors is the greenhouse thrips (_Heliothrips hæmorrhoidalis_). Thrips are readily controlled by means of nicotine-sulphate. CHAPTER VII. Leaf-Feeding Insects. Leaf-feeding insects have their mouth-parts developed for the biting off and mastication of their food; such insects are, in general, earwigs, crickets and grasshoppers, the caterpillars of moths and butterflies, beetles and their grubs, and the grubs of saw-flies. Such insects vary, not only in their period of activity, some feeding at night, others during the day, but also in the manner under which they set about it. Many feed exposed upon the surface of the plant, while others require protection, such as is afforded by the webbing together of leaves. Some feed upon the leaf epidermis only; some eat holes in the leaf-surface, or gnaw irregular notches from the leaf-edge; while the grosser feeders completely devour the whole. Earwigs.