280 INSECTS 



becomes also more difficult to reach them. It must 

 always be remembered that no contact poison can be 

 effective unless it actually touches the insect aimed at, 

 and covering the top of a leaf no matter how thoroughly, 

 when the insects are feeding on the underside, is of 

 little or no use. More ill success results from a failure 

 to recognize this fact, than from any deficiency in the 

 material applied. 



There are a large number of "patented" or pro- 

 prietary insecticides on the market for killing plant 

 lice, scales and similar insects, and some of these are 

 really meritorious; but they are usually expensive and, 

 in the long run, no better than the materials we have 

 just enumerated. 



While it is comparatively easy to reach and control 

 plant lice on most ordinary farm crops and in the 

 garden, it is decidedly more difficult to reach scales 

 whether soft or armored, and even mealy bugs are 

 difficult to kill, in spite of the fact that they are com- 

 paratively unprotected. 



There is only one period in the life of such insects 

 when they are within reach of mild applications and 

 that is when the young have just hatched and are 

 moving about without protective covering. Theoreti- 

 cally that is the best time to reach them and with some 

 species it is practically the only time. The oyster 

 shell scales and some others that attack our trees and 

 shrubs winter in the egg stage under the mother scale, 

 practically safe from all our known mixtures. Early 

 in the season, depending of course on latitude as to the 

 exact time, these eggs hatch, all at about the same time, 

 so that for two or three days there is a great swarm of 

 naked larvae, and for a week there are newly set scales 

 with the thinnest sort of protective covering; that is 

 the time for whale oil soap, kerosene emulsion, miscible 



