﻿an Economic study of acacias. 5 



according to various observations, is the cottony cushion scale 

 (leery a purchasi). 



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. 

 Scale 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. 1 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 (Oyelle 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 2 



• i "The Black Wattle," by Jared G. Smith, Bulletin No. 11, Hawaii Agricultural Experiment Station. 

 2 "Wattles and Wattle Barks," Sydney, 1906. 



