168 PRINCIPLES OF PLANT CULTURE 



lice, the squash bug (Anasa tristis) arid the oyster-shell 

 scale (Lepidosaphes ulmi). 



307. The eating insects may be subdivided into leaf- 

 eaters, those that devour the foliage; root-eaters, those 

 that devour the roots ; and burrowers, those that tunnel 

 through some part of the plant by eating a passage for 

 their bodies. 



308. The leaf-eaters include numerous species. They 

 are readily recognized by the fact that the leaves, on 

 which they feed, disappear more or less rapidly. They 

 may generally be destroyed by applying a poison to the 

 foliage, for which purpose the arsenical compounds are 

 well adapted (283). In cases where the use of a deadly 

 poison is unsafe, hellebore (289) or pyrethrum (290) 

 may be substituted. 



309. The root-eaters include fewer species than the 

 leaf-eaters and are usually more difficult to control. 

 Carbon bisulfid, injected into the soil about the roots of 

 cabbage and cauliflower plants, with an instrument de- 

 vised for the purpose has been successfully used to destroy 

 the cabbage maggot (Pegomya brassicae) and may be 

 found useful in other cases. Attacks of this insect have 

 also been successfully prevented by surrounding the stem 

 of the young plant with small cards of thin tarred paper. 

 One of these cards, the tool used for cutting them and 

 the manner of using the tool are shown in Figs. 75, 76 

 and 77. 



310. Burrowers, as the term is here used, include 

 not only the so-called borers that burrow within the 

 stems and roots of plants, and the leaf miners, that 

 live between the surface of leaves, but also the insects 

 that pass their larval stage within fruits. Insects of 

 this class are difficult to control, since they are mostly 

 beyond the reach of insecticides. 



