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INSECT ENEMIES. 
THE EUCALYPTS AND THEIR INSECT ENEMIES. 
The preying of insects upon plants is nothing new. It has been going on for 
ages over all the habitable land surfaces of the earth. Under ordinary conditions 
the process does not attract our attention. Our plants and trees are sufficiently 
vigorous to support easily the animals that live upon them as parasites or visit them 
adventitiously in search of food. A kind of balance or equilibrium is maintained 
between the vital resources of the plant and the animal demands made upon them. 
But the equilibrium may be disturbed or even permanently unsettled. The soil 
may after a time prove deficient in some of the mineral salts required by the plant. 
The roots of the plant may reach a stratum of dry shingle, or limestone, or hard 
rock. Temperature may rise too high or fall too low. The sky may fail of its 
wonted showers or pour down successive torrents and too heavily saturate the 
ground. The plant then declines in vitality. Parasites and visiting enemies 
multiply. Leaves and twigs die back; and then, if no relief be given, death invades 
the stem and roots. The introduction of other insects to prey upon those that have 
been preying upon our plants may greatly help. It may even restore the balance 
of forces. But for general and permanent remedy we must go deeper. 
Animals as well as plants become subject to an increasing burden of alien life 
whenever and wherever they fall below normal vitality. The enfeebled colony of 
bees develops disease or is robbed by stronger colonies. Lice multiply upon 
debilitated cows and horses, and ticks upon underfed sheep. There is thus some 
general law or sequence of cause and effect whereby poverty of sap in the plant or 
of blood in the animal is surely followed by heavier toll to the ever lurking enemy. 
Nature apparently decrees the destruction of the unadapted; and parasites, 
whether vegetable or animal, fill the role of agents in the destructive process. 
Gardeners, farmers, and tree planters should know their insect enemies and their 
insect friends. Every ally that will slay and clear away blights and pests should 
be encouraged. But our reliance everywhere must be first and mainly upon 
vigorous and well-sustained vitality. Animals must be well and suitably fed; 
trees must be planted where soil, rainfall, and temperature will combine to promote 
exuberant and resistant life. 
We are concerned here with the bearing of this truth upon the eucalypts. 
These trees as we see them in their native Tasmania and Australia are the hosts of 
countless Insect a and Arachnid a and of some vegetable parasites. Some of the 
insects are enemies; some friends. Some of the enemies are at their worst in the 
larval or grub stage; others in the mature or adult stage. Some are leaf-eaters; 
others sap suckers. Generally the vital forces are balanced. In favourable 
situations the trees flourish, grow to normal dimensions, and persist to their due 
term of life. Enemies are there, but the well-nourished life of the trees aided by 
the warfare of the friendly insects keeps them effectually under control. In hard 
conditions, a species will sometimes develop resistance by taking on a dwarf form 
and by thickening its leaves; but this is a slow process and requires a orood many 
years for its.completion. In some parts of Australia certain of the eucalypts are 
liable to be infested with vegetable parasites as well as animal enemies * These 
vegetable parasites are sap. suckers belonging to the mistletoe family (Lorantha- 
ceae). And here, again, it is the rapid-growing and vigorous individual trees that 
