THE INSECT WORLD. 



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biini, or forms like the ' ' peach-louse' ' or the ' ' woolly apple- 

 louse," where they may be on leaves, twigs, and roots at one or 

 different times. Bisulphide of carbon can be used with good 

 effect in such cases ; but it is rather an expensive application, and 

 there is an element of danger that makes it desirable to employ 

 something equally effective yet less liable to injure vegetation. 

 Very satisfactory results have been obtained with tobacco, some 

 under my own observations, some reported by other trained 

 observers, and it seems fairly well proved that trenching around 

 an infested tree, and filling into the trench a liberal supply of 

 ground tobacco, refilling the trench immediately after, will have 

 the effect of clearing the roots of these pests. This has been 

 used more particularly against the peach aphids, and has been 

 almost uniformly successful. Tobacco is a good fertilizer, and 

 many dealers carry the coarsely ground product as part of their 

 stock in trade. It is rather expensive as a fertilizer, but cheap as 

 an insecticide, and a double value is obtained because besides 

 killing the lice it also stimulates the trees or other plants. The 

 use of tobacco, therefore, where root-lice are troublesome, is 

 good farm practice. It may be well to say, however, that little 

 or no benefit is derived from the use of stems spread upon the 

 surface, or dug in, because there is not a sufficiently rapid extrac- 

 tion of the nicotine, and this is, after all, the killing agent. The 

 ground material on the other hand gives up its nicotine readily 

 to a small quantity of moisture, and it will be quickly carried 

 down and around the roots of the plants, into direct contact with 

 the insects. In land infested by root-lice the use of commer- 

 cial fertilizers is indicated. It has been found by experience that 

 salty mixtures kill plant-lice more or less rapidly, and therefore, 

 where root-lice are present, potash in the form of kainit and 

 nitrogen in the form of nitrate of soda are advisable. I have 

 frequently noticed that on land where these fertilizers are used 

 underground insect life is scant, and direct experiments have 

 proved that this condition of affairs is largely due to the salty 

 fertilizers introduced into the soil. As against peach-lice in light 

 soil, ten pounds of kainit to a five- or six-year-old tree of good 

 size is about right, and the material should be spread on the 

 surface evenly as far as the roots are likely to extend. 



In the more normal plant-lice the wings are better developed, 



