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AN ECONOMIC ENTOMOLOGY. 



While, as has been stated, we cannot lay down general rules 

 as to the treatment of all plant-lice, there are a few points that 

 are always important. In the first place, the earlier the insects 

 are dealt with, the more chance there is for the application to be 

 effective. Plant-Hce should be treated just as soon as they are 

 noticed ; the longer the delay the weaker the plants become, and 

 the greater the thoroughness required to reach all the specimens. 



As a general insecticide, nothing is better than the kerosene 

 emulsion, which, when diluted ten times with water, kills all the 

 young forms and adults of the green species. It has been found 

 by experiment that black or brown species are much more diffi- 

 cult to destroy, and one part of emulsion in six or eight parts of 

 water is more likely to be effective. Fish-oil soap is effective at 

 the rate of one pound in six gallons of water ; or, as against the 

 brown species, one pound in four gallons of water. Thorough- 

 ness of application is always essential. It must be remembered 

 that these poisons act by clogging the spiracles, or by entering 

 into the body through them. Unless the application is thorough, 

 the insects may be weakened but not killed, or, if rendered help- 

 less for a time, they may recover, and a second dosing becomes 

 necessary where one, more thoroughly applied, would have been 

 sufficient. Where it is not advisable to apply either of the ma- 

 terials mentioned, we can use tobacco with good prospects of 

 success, either as a decoction or a very finely ground powder. 

 In greenhouses, tobacco is a standard remedy, and its frequent 

 application results in keeping them moderately free from these 

 pests. It may be applied as already described, but is more usu- 

 ally burnt to make a smoke, which is poisonous to the insects. 

 A milder method is to keep the steam-pipes covered with moist 

 stems, so as to produce a nicotine-laden atmosphere. Very often 

 plant-lice appear in forcing-beds, and these we can generally 

 destroy with bisulphide of carbon placed in a shallow dish and 

 left in the covered beds overnight. Greenhouse benches may 

 be rid of the pests in the same way, covering the plants for two 

 or three hours with a frame or box, and evaporating a small 

 quantity of the bisulphide. A fumigating-box made of wood, 

 canvas, tin, or other material, large enough to contain potted 

 plants of good size, should be in every greenhouse and nursery. 

 A number of pots of infested plants may be placed in such a box, 



