58 INSECTS INJURIOUS TO VEGETABLES 



and are so dark and evidently secretive in their nature as to 

 usually escape recognition. When, however, an undue increase 

 in numbers takes place and the habit of moving in armies is 

 assumed, their presence becomes manifest, too late, however, 

 in most instances, for remedial treatment. Transformation to 

 pupa takes place in little earthen cells, but occasionally pupae 

 are not so protected. 



Methods of Control. — In the case of large armies in ex- 

 tensive fields, poisons are of little value when outbreaks are at 

 their height. When the armies are first noticed the "worms" 

 are as a rule approaching maturity, they have effected much 

 damage, and it is difficult at this stage to prevent them from 

 passing from one field or other tract to another. It follows 

 that, although arsenical poisons are valuable in many cases, we 

 must place more reliance in preventives such as cultural and 

 mechanical methods. 



In fields of young grain and on lawns many "worms" may 

 be killed by crushing with a heavy roller, when the insects are 

 at work early in the morning or toward dusk. In fields that 

 are injured beyond recovery, sheep or other cattle may be 

 turned in in numbers with benefit, as they will kill the larvae 

 by trampling upon them. 



Other useful methods of this nature include trenching or 

 ditching, or plowing deep furrows in advance of the traveling 

 hosts to entrap the larvae which will fall into them, and here 

 they may be crushed by dragging logs or pieces of brush through 

 the furrows. If possible to fill the trenches with water, or if 

 they become partially filled by rains, the addition of a small 

 quantity of kerosene, so as to form a thin scum over the surface 

 of the water, will prove fatal to the "worms." 



Rotation of crops should always be practiced, as well as 

 burning over fields when they are too badly infested to recover. 

 Above all other precautions necessary to secure immunity from 

 attack is that of keeping the fields free from volunteer grain 



