AN ECONOMIC STUDY OF ACACIAS. 5 
according to various observations, is the cottony cushion scale 
(Icerya purchast). 
The scale insects have sucking mouthparts and subsist on the 
juices from the inside of the tree; for this reason they are hard to 
combat, because it is difficult to poison their food supply. Since 
they live upon the sap, they must necessarily lessen the vitality of a 
tree, especially where there is a very dry summer climate. If they 
are very numerous, trees can not thrive and may even be killed. 
Seale insects, besides robbing the tree of nourishment, harm the 
tissues, close the pores by their excretions, and supply conditions 
under which fungi may get a good start. All these are much less 
serious with the acacias than the actual loss of sap; and where 
the water supply is ample the actual harm done by the scale is very 
slight. But since one of the chief values of the _acacias is their 
adaptability to very arid regions, the scale insects should be destroyed 
wherever they exist, and care should be taken to establish plantations 
from seed or from thoroughly disinfected plants. 
Two insect enemies of the wattle in Natal, reported by Mr. David 
G. Fairchild, are a bag worm, which destroys great quantities of 
foliage and checks the growth of the trees, and a more destructive 
locust, which can retard growth to the equivalent of more than a 
year. The bag worms are collected and burned, and the plague of 
locusts is prevented by spreading poisoned molasses about their 
breeding places. <A special locust expert is employed by the Natal 
Government; with his corps of laborers he poisons all the principal 
breeding places of the pest. | 
Other insects attack the black wattle (Acacia decurrens) in Austra- 
lia.t Of these, one is an undescribed species of weevil (Bruchus sp.) 
which was found in seeds purchased in San Francisco, and pre- 
sumably was introduced into California from Australia or South 
Africa in the seed. Another is a long-horned beetle (Cyelle crini- 
cornis) of almost world-wide distribution in the Tropics; several 
other insects do more or less harm. 
° FIRE. 
There seem to be various opinions about the fire-resistant qualities 
of acacias, though they are generally considered very sensitive to 
fire. Some authors have stated that they do not burn readily, 
and the wattles in particular have been recommended for planting 
as fire breaks, not so much because they are not easily ignited but 
because their growth is so dense, both above and below ground, that 
no ground cover can thrive, and there is, therefore, beneath the trees 
an area free of vegetation. On the other hand, Dr. Maiden says ’ 
1“The Black Wattle,’ by Jared G. Smith, Bulletin No. 11, Hawaii Agricultural Experiment Station. 
2“Wattles and Wattle Barks,’’ Sydney, 1906. 
