296 



A.Y ECONOMIC EXTOMOLOGY. 



application of an arsenical spray in the infested patch and imme- 

 diately surrounding it is beneficial in some cases, but there is the 

 practical difiiculty that grasses do not hold a water spray easily. 

 Using soapsuds instead of pure water will overcome this, how- 

 ever. If the insects become abundant enough to start on a 

 march, a narrow strip can be ploughed in its line, harrowed and 

 rolled, and then the roller can be kept going, crushing the insects 

 as they come upon it. Or a very strong kerosene emulsion may 

 be sprayed upon the caterpillars as they advance, and upon the 

 fields that they are leaving. There will be no vegetation that 

 need be considered, and therefore the mixture need be diluted 

 five times only, which will be eftective even against the nearly 

 full-grown larv^. It would seem that following one army of 

 caterpillars we would have next year a still more destructive in- 

 vasion, but such is not usually the case. Fungus and other dis- 

 eases appear and decimate their ranks, their enemies increase 

 rapidly after the first large brood, and the result is that normal 

 numbers only survive, unless the conditions which favor their 

 increase one year continue also the next. As the land becomes 

 more cut up and cultivated, the danger from this insect is 

 correspondingly lessened, and where a reasonable amount of 

 promptness is displayed on its first appearance no wide-spread 

 injury need be anticipated. Everything depends upon the 

 promptness and thoroughness with which early measures are 

 adopted and carried out, and all delays will pro^-e costly. 



A near relative of the true " army-worm" is the insect known 

 as the "wheat-head army-worm," Leiccania albilinea. This is 

 a rather brighter larva, also striped with yellow, never becoming 

 quite as large as its ally, and peculiar in the habit of eating the 

 grain or seed of wheat, rye, and other grasses. There are two 

 broods of this insect also during the year, but that which does 

 the injury makes its appearance in the nearly full-grown larval 

 condition just when the grain is ready to ripen. At this time, 

 when sufficiently numerous, their injuries to the crop are severe, 

 because a single caterpillar may in a few minutes practically de- 

 stroy the value of an entire head of wheat. The ears become 

 rao-Q-ed and the surface of the soil becomes littered like a barn 

 floor after threshing. The moths from which these insects are 

 derived expand a little more than an inch, and are of a rather 



