100 



THE COCO-NUT 



CHAP. 



Being a sucking insect, the scale will not eat any 

 poison. If it is deemed necessary and worth while to 

 attack the scale directly, the ordinary kerosene emulsion 

 will in most places be the best weapon. As the 

 emulsion is to be applied to the leaves it must not be 

 too strong. An emulsion of palm oil and soda is safer ; 

 it has been used in Togo and found entirely effective, 

 but at an altogether prohibitive cost. This will be 

 found true in general of any direct attack on the scale. 

 It is of course possible to spray a bearing coco-nut tree, 

 or to enclose it in a tent or balloon and disinfect it with 

 hydrocyanic acid — a method gaining in favour in the 

 fight against the San Jose scale ; but such measures 

 are not in general practically worth while. The treat- 

 ment is very costly in proportion to the value of the 

 tree ; if the tree is healthy it is not likely to suffer 

 much from the scale ; and if it is susceptible it is not 

 worth much, and is sure to be attacked again. 



The chief check on the coco-nut scale is furnished by 

 its natural enemies, foremost of which are lady-birds of 

 the genus Chilocorus. In Cuba, in the Philippines, 

 and probably in almost the whole range of the scale, 

 these predaceous little beetles are found with it. If 

 for any reason the scales become numerous, the food 

 of their enemies thereby becomes abundant ; and the 

 latter multiply and the scale is suppressed. 



Schwartz, writing in Der Tropenpflanzer, has urged 

 that the attempt to combat any pest by means of 

 parasites on it is of necessity futile, and that reliance 

 can never be placed on natural enemies to prevent injury 

 from a pest. It is obviously true that its parasites 

 cannot exterminate a pest. They reduce it in number 

 until there is no longer support for the parasite, but 

 the parasite is the one which will usually disappear 

 first. Practically, however, it must be maintained that 

 when a pest has been so reduced that its parasites can 

 no longer maintain themselves upon it, it must itself 

 have ceased to be a pest. It is beyond question that 

 Aspidiotus destructor is itself kept in check in this way 



