CHAP. XI.] THE CONTROL OF INSECT PESTS OK CROPS. 



insects or of th fungi or bacteria. The use of the knife 



in such cases, though apparently drastic, is usually quite successful. 

 Mango-trees especially are subject to attack by a common tree- 

 boring beetle larva [Batocera rubus) anil Orange trees also are 

 affected by the grub ol anothi i Sometimes I grub can 



be killed or pulled out with a piece of wire but usually it is b 

 to cut down to it and clean out the gallery which is othei 

 likely to give access to other diseases later on. Apiece of wire 

 with a barbed point is used for destroying palm beetles (Oryctes 

 rhinoceros) in their burrows in the tender shoots of palms, the beetles 

 being transfixed on the barb and withdrawn and the burrow 

 tarred 



A tree or portion of a tree which is dying or dead at 



Omes a suitable breeding-place for innumerable insects, mostly 

 beetles, which teed upon dead or decaying wood, and some of these 

 may be a source of danger to living trees if no more dead wood 

 i- available tor them. All dead trees and branches should 

 therefore be lemoved and used for fuel or other purposes and not 

 Ik left standing or lying about the field-. This is especially the 

 with rotting stumps of palms and aloes which are usually 

 found to be swarming with the fat white grubs of Oryctes which 

 will presently emerge as beetles to attack the palms in the 

 vicinity. 



Cereals, such as sugarcane, cholam and paddy, generally 



exhibit signs of attack by stemborers by a withering of the central 



1 which is frequently completely detached so that it comes 



away from the plant at the leas) pull. Such a withered central 



i1 is called a " deadheart " and its presence almost invariably 

 -hows that a caterpillar is boring inside the stem of the plant. 

 A watch should be kept for the first appearance of such dead- 

 hearts, especially in a valuable crop such as sugarcane, and they 

 should be rigorously cut out and the caterpillar killed to prevent 

 the attack from spreading. Shoots so attacked are in any i 

 quite useless ; whereas, if they are cut back as soon as noticed, new 



>ts will generally be thrown up and little loss result. But the 

 importance of prompt cutting out of deadhearts lies in the preven- 

 tion of further damage b) latei In Is of the insects concerned. 



riCIDAL METHi 



Insecticides, a- their name implies, are substances which are 

 used to kill insects. A- a rule, they are only used when an ins 

 ha- attained such numbers as to be a pest. Some insecticides, it is 

 true, may be and are used a- deterrents or repellents, to drive 

 insects away temporarily from particular areas, but as ,i rule it 



