36 



'''' Back firing ^"^ a somewhat old-fashioned practice, is of great use in 

 destroying army worms, cutworms, and other forms of insects when 

 they occur in such numbers as to ruin a crop. It consists in burning 

 a rather wide stretch in advance of the wind at the farthest extremity 

 of the field, and then stamping this out to prevent the fire from reach- 

 ing other fields beyond. The field is then burned, beginning with the 

 side from which the wind is blowing. This has the efi'ect of destroj'ing 

 the entire field, with all the cutworms and many other insects which 

 it contains, with practically no danger of the fire spreading to fields 

 where it is not desired. 



When cutworms assume the habit of traveling in armies they should 

 be treated in the same manner as advised against the army worms. 



ARMY WORMS. 



In addition to the arm}" cutworm that has been mentioned and the 

 variegated and spotted cutworms, which sometimes exhibit the same 

 migratory tendency, there are three important species of beet-feeding 

 caterpillars, allied to the cutworms, but lacking the true cutworm 

 habit. The most important of these is the beet army worm. 



THE BEET ARMY WORM. 



( Caradrina [Laphygma] exigua Hbii. ) 



In the 3'ear 1899 this species, which had not previously attracted 

 attention by its ravages, became prominent as an enemy to the sugar 

 beet in Colorado. Subsequent study showed that it had been observed 

 at an earlier date attacking crop and other plants in New Mexico and 

 in California. It is an imported pest, and, although not at the present 

 time of great importance, bids fair, in course of time, to become a 

 serious eneni}^ to the cultivation of sugar beet in America. It has 

 evidently come by way of California and is traveling eastward, a 

 method of migration of which there is precedent in the Colorado 

 potato beetle. 



The moth (fig. 32, a) is mottled gray, resembling the plain form of 

 the related fall army worm. The fore-wings are broader and paler, 

 and the reniform and other markings are more distinct. The wing 

 expanse is less than an inch and one-half. The larva is rather slender, 

 with a small head, and the body greenish or olivaceous and striped as 

 shown (fig. 32, I, c, and fig. 33). 



When migrating, the beet arnw worm attacks several forms of veg- 

 etation. Sugar beet appears to be the favorite host plant; table beets 

 are also relished, and it feeds quite as well on lambsquarters, pigweed, 

 and saltbush (Atriplex). When numerous, corn, potato, pea, onion, 

 sunflower, and the leaves of apple, mallow, Nlcot'mna gJauca^ Cleome, 

 plantain, and wild grasses are eaten. In southern California the moths 

 appear in April and until June; caterpillars of the first generation 



