440 



AN ECONOMIC ENTOMOLOGY. 



Wet up the copper carbonate in a quart of water, add to it the 

 ammonia, and when completely dissolved and diluted with the 

 water the compound is ready for use. 



Holding a sort of intermediate position between stomach and 

 contact poisons are powdered white hellebore and tobacco, both 

 of which may be used pure in the form of either a finely ground 

 powder or a decoction. Hellebore has a very narrow range of 

 effectiveness, and is particularly useful only against saw-fly larvae 

 like the ' ' currant-worm. ' ' If used dry, it can be dusted on pure 

 or mixed with twice its own weight of land plaster or cheap 

 flour, and will kill by being eaten or by coming into contact with 

 the insects. If a spray is preferred, it is generally effective within 

 its range at the rate of one ounce in two quarts of water, and 

 sometimes, in the case of young saw-fly larvae, one ounce in one 

 gallon of water will be sufficient. The material should be steeped 

 in one pint of boiling hot water, and the cold water added grad- 

 ually. The sediment can be sprayed on with the liquid, or it 

 can be thrown away and only the extract used. The decoction, 

 at the rate of two ounces in one gallon of water, has been highly 

 recommended against the cabbage-maggot, but the reports are 

 too contradictory to make it advisable to rely upon it for that 

 purpose. 



Tobacco has a very much wider range of usefulness ; few in- 

 sects care to eat of it, and a plant thoroughly sprayed with a decoc- 

 tion is safe from the attacks of flea-beetles and a great variety of 

 other insects. It is as effective against the saw-fly larvae as is 

 hellebore, and may be applied in much the same way. It may, 

 in many instances, be applied at the base of plants to keep off 

 borers and root-feeders generally : for instance, against the cab- 

 bage-maggot, a handful of tobacco dust at the base of each plant 

 will usually serve as a tolerably complete protection. It is as a 

 contact poison that it has the greatest advantages, and it may be 

 used effectively against plant-lice, either in a dry powder or in 

 decoction. If used as a powder, it is very important that it 

 should be as finely ground as possible. All contact poisons kill 

 through the stigmata, or spiracles. The fine dust makes its way 

 through the breathing pores into the trachea, and sets up an irri- 

 tation which results in the death of the insect. The coarse par- 

 ticles are sifted out by the protective structures with which most 



