As far as regards the injurious species of Coccids it may usually be taken for granted that those infesting deciduous plants (class _a_) live chiefly on the bark (class _c_), and are either naked (class _h_) or covered with a hard scale (class _f_). If naked they are chiefly _Lecanium_; if covered, either _Mytilaspis_, _Aspidiotus_ or _Diaspis_.
_Icerya_ is exceptional, being omnivorous, feeding equally on bark or leaves, deciduous or evergreen plants; it belongs to every class except (_f_). Every method of destruction has therefore to be resorted to against it.
The treatment of a deciduous plant infested by Coccids is simple as to its method. For two reasons the dead winter-time must be chosen for it--first, because, the leaves being off, the whole plant can be easily got at; secondly, because the eggs of the insect have not yet been hatched, and the whole brood can be destroyed at once. The first operation should be the pruning of the tree, so as to reduce the labour required to a minimum. A brushing over all the trunk and branches with a good hard stiff brush and one of the liquid remedies given below is then often successful. Brushing with a _dry_ brush is adopted by some persons; but, although this doubtless clears away a good many insects and scales, and may do the tree itself some good by cleaning off fungus-growths and incrustations, yet it necessarily fails to destroy all the eggs, and in consequence the work is only half done. _Any one who wishes to extirpate Coccids must make certain that he has destroyed the eggs_--a fact which is quite ignored by numbers of those who glibly talk of their own success, and blame the advice of others. The object being, therefore, twofold, the operation should be performed with a hard, stiff brush dipped in one of the fluids recommended below; and care should be taken that there is no part of the trunk or branches escaping untouched. In fact, what should be aimed at is a kind of painting of the tree, but with a thin coating of the fluid, so as to close the pores as little as may be; while at the same time the brush clears away as many as possible of the "scales" and their enclosed broods of insects and eggs.
Bearing in mind what has been said just now of the want of _certainty_ in any remedy whatsoever, the tree-grower who follows these directions will most likely find his work successful and his deciduous plants cleaned of "scale" on the bark.