PAEIS-GEEEN. 



77 



water-barrel on two wheels, something of the nature of that known as 

 the Farringdon Hop and Plant -washer, was found to answer excel- 

 lently. A fine spray could be thrown by these means to a height of 

 forty feet, and expense saved of buying new apparatus, which very 

 likely would not have answered nearly so well. 



Other kinds of apparatus suited to the purpose, on a more elaborate 

 and expensive scale, will be found named in implement-makers' cata- 

 logues. 



Different methods of action of insecticides. — Amongst the very large 

 number of letters which were sent me in the past season regarding the 

 use of Paris-green, such a large proportion were with reference to its 

 possible serviceableness in killing Green-fly or Aphides, that a few 

 words may be of service as to the method of action of insecticides. 

 Many kinds of insects, or of insects in their early stages, such, for 

 instance, as the caterpillars of moths or of sawflies, or beetles and their 

 grubs, feed by biting and swallowing the leafage or shoots, or whatever 

 portion of the plant they may attack. 



For all these kinds of infestations the applications of Paris-green, 

 London-purple, or any other dressings which are poisonous to insect- 

 life, but which can be used without damage to the leafage, or to the 

 user, will be found effectual if they are so applied that the caterpillar 

 or beetle cannot consume its food ivithout consuming the poison adhering to 

 it at the same time. 



But with such kinds of insects (Aphides or Plant-lice, for instance) 

 as feed by piercing into the substance of their food-plants with their 

 mouth-suckers, and merely draiving up the juices from beneath the surface 

 instead of biting and swallowing the surface, together with what may 

 be on it, the case is different. It may so happen that they or some of 

 them may be killed by a mere superficial poisonous dressing (as of 

 Paris-green, for instance) on their food, but it is by no means certain. 

 The sucker goes down into the juices below the surface, and, excepting 

 where the poison in some way or other may go down also to where the 

 food is being pumped up from, the insect is not likely to be injured by 

 poisoning. We need for these sucking insects something that will kill 

 by contact, which Paris-green does not do. Therefore (as we all know) 

 soft-soap washes, which are especially injurious by adhering to the 

 insects and choking their breathing-pores, are the best foundation for 

 washes to destroy Aphides, with additions of quassia, paraffin, tobacco > 

 or anything else, according to the views of each grower, which may 

 make the wash most deterrent. 



Working on the principle of arranging a compositiun of wash which 

 would act by poisoning or choking respectively the different kinds of 

 insects on which it was brought to bear (in mixed attacks), or possibly 

 acting in both ways at once, a consideration arose early in the past 



