INSECTS INJURIOUS TO AGRICULTURE. 197 



destructive in a wet summer succeeding a dry one, at the 

 time when the wheat is in the milk. The caterpillar state 

 lasts a month; the chrysalis state two weeks, unless it hiber- 

 nates. 



The caterpillar is an inch and a half long; the head is 

 covered by a network of confluent spots, and along the 

 middle of the face run two lines diverging at each end. A 

 light-colored waved line just above the legs is succeeded by a 

 dark one, then a light one edged with two thread-lines; 

 while the upper part of the body is dark, with an inter- 

 rupted white thread running along the middle of the back. 

 The moth is rusty, grayish-brown, sprinkled with black 

 specks; and the species is called unipuncta from the single 

 white discal dot of the fore wings. 



REMEDIES. The best preventive remedy is to burn meadows and 

 grass-lands, where the eggs are laid, iu autumn. When the armies 

 are in motion and threaten a field of wheat, the latter should be 

 protected by a deep trench with steep or undermining sides, in 

 which fires are kindled or kerosene is poured. The use of the ditches 

 may be supplemented by dusting the grass or wheat for a few feet 

 on each side of the ditch with Paris green. 



The Wheat-head Army-worm (Leucania alMlinea). This 

 caterpillar injures the heads of wheat, rye, and barley, begin- 

 ning at the base, sometimes at the centre of the ear, some- 

 times hollowing out the soft grains, leaving nothing but the 

 shell and the chaff. The caterpillar is like the foregoing 

 species, but is striped with sulphur-yellow and light and 

 dark brown lines. The insect is common from Maine to 

 Kansas. 



The Wheat Thrips (Thrips tritici of Dr. Fitch). 

 This is an exceedingly minute, active, long, narrow, leap- 

 ing insect of a bright yellow or shining black color, occur- 

 ring in numbers on the heads and stalks in June and July, 

 puncturing and thus exhausting the juices of the kernels, 

 and rendering them dwarfish and shrivelled. Another 

 kind common on wheat in New York, in June, is the three- 

 banded Thrips (Coleothrips trifasciataYiich}. 



Other wheat-insects are certain species of Oscinis,Chlorops } 



