PLUM APHIS(_Rhophalosiphum nymphææ_).--This insect is sometimes very common during spring upon the shoots and leaves of plum in New Zealand; in other countries it has been found to migrate to and infest the flowers and leaves of water lilies. The insects assume various shades of green, the winged females having the head, thorax, and legs blackish; the “honey-tubes” vary in colour, and may be reddish, blackish or yellowish. POPLAR GALL APHIS(_Pemphigus pupuli-transversus_).--Upon the leaf stems of poplar trees in many parts of New Zealand sac-like growths (Fig. 9, 7), measuring anything from half an inch to one inch in length, may be found. These are the galls formed by the North American poplar gall aphis. In each gall are colonies of the aphis surrounded by a mass of flocculent secretion. The walls of the gall are thick and tough, with the outer surface wrinkled, while at the end, toward one side, is a slit-like, or sometimes circular, opening surrounded by a thickened rim, presenting much the same appearance as the mouth of a sack gathered together and tied. For the most part, these insects are wingless females only, but during the summer, and particularly toward the end of autumn, winged females develop and migrate to cruciferous plants, such as cabbage, rape, mustard and turnips, or weeds allied to these cultivated forms, upon the roots of which they establish colonies surrounded by a woolly secretion. In spring a return migration to the poplar takes place, and galls are again established. Leaf-hoppers. Leaf-hoppers form a group of small, narrow-bodied, sap-sucking insects; as the name implies, they infest the foliage of a variety of plants, and when disturbed have the habit of suddenly leaping or hopping to safety; the species present in New Zealand are usually of a greenish or yellowish colour. The adult insect is winged (Fig. 8, K, L), and the female lays her eggs in the plant tissues (H); from these eggs the young wingless hoppers (I) hatch and attack the plant; as they grow, wings develop (J), but until then the insect depends for locomotion upon its hopping powers. The most outstanding species in New Zealand is the apple leaf-hopper (_Typhlocyba australis_). This insect causes considerable damage to apple trees unless controlled, which can be effected by spraying with nicotine-sulphate against the young insects in the spring. White-flies.