XX Remedial Measures and Insecticides. 



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 

 3000 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 considered 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 internally through the alimentary system. The pro- 

 prietors of patent insecticides not unnaturally object to disclose 

 their formulae, and put off any questions by asserting that the 

 amount of active poison in the mixture is so very small as to be 

 practically harmless. This may very well be true in most circum- 

 stances ; 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 arsenic or 

 other mineral poisons for their killing properties are of little use 

 against Coccidc^. 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 useful only against pests such as cater- 

 pillars, grubs, and slugs, that take in solid food. Mr. Maskell puts 

 the matter concisely. He says : * Whatever damage is done (by 

 scale insects) is effected by the sucking of the juices of the plant 

 through the rostrum (beak) of the insect. It follows from 

 this that applications of any fluid to the tree externally, with the 

 object of poisoning the insects in their feeding, would be useless, 

 as their food is drawn from beneath the surface.' * 



There are many substances fatal to insect life, but perfectly 

 harmless to the higher animals, that may be safely used. A list 

 of the principal insecticides, with directions for their preparation 

 and application, is appended. {See pp. xxxi et seq.) 



* New Zealafid Scale Insec/s, p. 26. 



