INJTTRlOtJS INSECTS 



303 



Insecticides. In dealing witli insects directly, we 

 Lave three classes to combat: 



1. Those with biting month-parts, having jaws, and 

 masticating their food. 



2. Those with sucking month-parts, having a beak, 

 through which fluid nourishment is taken. 



3. Insects of either of the above classes., but inac- 

 cessible, such as insects on roots of trees or in bins 

 of grain. 



For Insects that Chew their Food. 



ARSENITES. Since the first class bite off portions 

 of their food, it is evident that poisonous substances 

 placed thereon will be taken into the digestive system 

 with the food. 



SPRAYS. -Paris green, an aceto-arsenite of copper, 

 contains, when pure, about 58% of arsenic. The 

 amount of arsenic contained is variable. An average 

 analysis is: arsenic, 47.68%; copper oxide, 27.47%; 

 sulphuric acid, 7.16%; moisture, 1.35%; insoluble 

 material, 2.32%. In water, Paris green is practically 

 insoluble. The spray formula generally used is Paris 

 green one pound, freshly slaked lime two pounds, and 

 150 gallons of water. The addition of the lime is to 

 prevent any caustic injury to the foliage. This for- 

 mula varies somewhat with the plants sprayed. It can 

 be used upon potatoes, apple trees, and most species of 

 shade trees. For stone fruits the amount of water 

 should be doubled, since leaves such as peach leaves are 

 easily injured by arsenites. This spray when being 

 used must be kept in a constant state of agitation, or 

 the poison will settle. The liquid at the bottom of the 



