Page:A primer of forestry, with illustrations of the principal forest trees of Western Australia.djvu/115

109 to the ravages of termites, or white ants, in Australia, it would probably be found that these insects hold a place unrivalled by any in economic importance.

Broadly speaking the habits of all species are very similar. The popular acquaintance with the termite or white ant is mainly derived from witnessing the nights of the winged forms of this pest. They emerge from cracks in the ground or from crevices in buildings, swarming out sometimes in enormous numbers. These winged individuals are not the ones that do the damage, but are the colonising forms. The real depredators are soft bodied, large headed, milky white insects, which are found under cover in tree trunks, logs, stumps, walls, and floors of buildings, etc. These are the workers and soldiers.

The food of white ants is the finely divided material into which they bore and from which they seem able to extract nourishment. White ants are somewhat cannibalistic and will devour their own cast skins and dead. It is this habit that largely aids in the poisoning of a nest. Those that die from the poison are eaten by the remaining members of the nest and they in turn are poisoned. White ants cannot endure bright light. In all their operations, therefore, they carefully conceal themselves. In this way the damage which they may be doing is often entirely hidden until perhaps a tree is blown down, when their work of quiet destruction is revealed. There are many other forest insect pests that cannot here be dealt with.

PRINCIPAL MEASURES OF CONTROL.

The ordinary spraying and similar methods employed in dealing with fruit and shade tree insects are, of course, not available for practical application in the case of forest trees.

In all efforts to control an outbreak or prevent excessive loss from forest insects it should be remembered that as a rule it is useless to attempt the complete extermination of a given insect enemy of a forest tree or its product when once widely established. Our efforts must be directed to reduce the conditions which favour the undue increase of a pest, that may result from forest mismanagement or negligence. Under complete forest sanitation, we can in a large degree prevent the favourable conditions for destructive insect propagation, and can aid in the propagation of beneficial insects, animals, and birds.

Were it not for the natural checks and natural factors of control of some of the more destructive insect enemies of forest trees and products, artificial control in many instances would be impossible. The insects and birds which prey upon destructive insects are also themselves subject to natural enemies and have therefore their limitations for good.

We can best assist our natural insect and bird friends in their efforts to maintain the balance of nature by our alliance with them, in adopting all measures which will weaken the forces of insect depredation, below the power of making an aggressive outbreak. This is largely accomplished by the destruction by cutting and burning of insect infested trees. This must be done at the right season, and hence it is necessary to know the life history of the pest before control measures can be suggested. It is of no avail to burn a tree after the pest which caused its death has issued. Trees planted or growing in unhealthy conditions will be more subject to insect invasion than trees which are planted in healthy localities. Therefore, unhealthy trees are better destroyed and only trees planted that will tolerate the conditions. As far as possible all forests should be kept in a healthy condition by good drainage and the prevention of fires. Fires are largely avoided by the creation of fire breaks. These are cleared narrow strips of country which divide the forests into given areas and thus make it possible to confine a fire, should it break out, to the one block. Trees damaged by fire or other artificial means are