122 AN ECONOMIC ENTOMOLOGY. 



abundant and correspondingly more troublesome southward. A 

 species sometimes occurs in considerable number on orange. As 

 the insects live exposed in all stages, they are easily reached by 

 contact poisons, and of these the kerosene emulsion is usually the 

 most satisfactory. It kills them in all stages at moderate strength, 



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one part of emulsion in ten or twelve parts of water being ordi- 

 narily sufficient. Whale-oil soap is quite as effective, and is 

 preferable on some house or conservatory plants, while even the 

 pyrethrum extract is useful on a small scale, and is, perhaps, the 

 cleanest of all on house-plants. 



