Plants as Affected by Aitimal Parasites. 157 



281. Repelling insects by means of offensive odors is 

 partially effectual in some cases, as with the squash-vine 

 borer.* Corncol)s or other objects, dipx^ed in coal tar 

 and placed among the plants, repel many of the moths 

 that produce the borers. 



282. Hand Picking, i. e., removing the insects from the 

 plants by hand, is the most satisfactory method for de- 

 stroying certain insects, as the tobacco- or tomato \vorm,f 

 and other large caterxjillars, and the rose-beetle. J A 

 vessel of watei' with a little kerosene on the surface, in 

 ^Ailich to throw the insects as they are gathered, is a con- 

 venient way of destroying them. In some cases, the in- 

 sects can be shaken or knocked from the plant directly 

 into the vessel. This method is often employed in de- 

 stroying the potato beetle. § Digging out cutworms and 

 white grubs 1 1 from al h )nt corn and strawberry plants, 

 and cutting out borers from trees and squash vines are 

 often the most effectual methods for destroying these 

 insects. 



283. Destroying Insects by Poisons or Caustics is the 

 method most generally available. The material used is 

 called an insecticide ( in-sect'-i-cide), and if satisfactory, 

 must be destructive to the insects without injuring the 

 l)lant to which it is applied, or rendering the plant or its 

 products unfit for food. The insecticides in most gen- 

 eral use are certain compounds of arsenic (Paris green, 

 London purple, white arsenic), hellebore and pyrethrum 

 powders, tobacco, kerosene and various compounds of 

 soda and potash. With the exception of kerosene and 



* MaUtia c-eto. t Phlegethontlus celeus. % Macrodactylus subspinosus. 

 I Doryphora deeemlineata. || Lachnosterna. 



