121 



The above treatment is suitable onlv for such plants as may be cut 

 down without permanent injury. We may now consider the case of 

 some larger tree to which this method would be inapplicable — say an 

 orange or cocoa tree. In this case the gas treatment is the most suitable. 

 The application should be repeated after an interval of about a fort- 

 night, to ensure the death of larvae subsequently hatched from eggs 

 that may have survived the first operation. Full directions for gas 

 treatment are given in the next Bulletin. 



In other cases a combination of these two methods might be adopt- 

 ed. If two or three coffee trees should require treatment, all superfluous 

 branches might be pruned, dipped, and burned, and the standing trees 

 fumigated with gas. Modifications of the treatment will be required to 

 suit particular cases. 



When a serious pest has once firmly and widely established itself, 

 little hope can be entertained of exterminating it, though much mav 

 still be done to keep it in check. 



Where trees are large and more or less detached, as in orange 

 groves, and the crop a valuable one, the gas treatment is again the 

 most satisfactory one. But where the cultivation is denser, and the 

 crop not so concentrated, spraying is found to be more practicable. 



The choice of the insecticide must be regulated by the nature of 

 the crop. Arsenious compounds cannot be safely applied to food crops 

 — such as fruit and vegetables — during the cropping season. And they 

 can on no acccunt be recommended for such a product as tea, unless 

 employed exclusively after pruning. For, however minute may be the 

 actual amount of active poison deposited on a single leaf, when we 

 consider that it takes some 400 lbs of leaf to make sufficient tea to fill a 

 chest, and that about 3,000 of the green leaves go to the pound, or 

 12,000 leaves to a pound of the finished product, it is evident that the 

 amount of poison in a single chest of tea might be considerable. And 

 further, during the processes of packing and transport, it is by no means 

 improbable that this, mineral poison which would dry off in fine powder 

 might gravitate and become condensed towards the bottom of the chest, 

 with dangerous results to the consumer. The danger may be consider- 

 ed far-fetched ; but I think it should be recognised. 



For the above reasons no patent preparations should be employed 

 to any large extent, unless the ingredients are well known. Such 

 mixtures, being designed for general use, may contain several different 

 poisons acting in different ways, either externally by contact, or inter- 

 nally through the alimentary system. The proprietors of patent insec- 

 ticides not unnaturally object to disclose their formulae, and put off any 

 questions by asserting that the amount of active poison in the mixtue is 

 so very small as to be practically harmless. This may very well be true 

 in most circumstances ; but, as shown above, in other cases the poison 

 might become concentrated into a small portion of the product. 



For other reasons compounds that depend upon arse nic or other 

 mineral poisons for their killing properties are of little use against 

 Ooccidae. Insects that subsist upon the sap of the plants should be 

 treated with insecticides that kill by contact, such as soap, petroleum, 

 pyrethrum, &c. Arsenic, which adheres to the surface of the plants, is 



