Control is effected by the agency of the ladybird, but epidemics sometimes occur with which the beetle cannot immediately cope; in such a case fumigation in the glass-house, or spraying with red oil in the open, should be resorted to.
Mealy Bugs.—Mealy bugs are characterised in the female by the nature of the waxy protective secretion which forms a powdery meal-like covering over the body, but is developed as a fringe of leg-like processes at the side ([Fig. 6]b); these processes at the posterior end of the insect may be prolonged as longer or shorter tail-like appendages in some species, or they may be no longer than those fringing the body margins in others. Immediately after each moult the larvæ are devoid of mealy covering and lateral processes, which are secreted anew each time the cuticle is shed. In a mealy bug colony are numerous small, narrow cocoons, in each of which a developing male insect lies.
Most mealy bugs produce eggs, which are laid in a spacious, cottony sac secreted at the posterior end of the female; the female insects, egg sacs, and male cocoons together form characteristic woolly masses on infested plants.
The injury caused by mealy bugs may be considerable, not only through the drainage of plant sap, but also owing to the production of honey-dew and its consequent sooty mould. All parts of plants are subject to mealy bug attack, and the insects are frequently attended by ants.
FIG. 6.
(a) Cottony cushion scale. (b) Mealy bug. (c) The black olive scale. (d) Gum tree scale: On right, females on twig; upper left, male scales; lower left, the ladybird beetle; centre, scales destroyed by beetle. (e) Hemispherical scale. (f) Fruit lecanium scale.
Photographs by W. C. Davies, Cawthron Institute.