2 CIRCULAR 8 4 9, U. S. DEPT. OF AGRICULTURE 



assume the army habit and move in large numbers along a more or 

 less definite line of march in search of food; then they are called 

 army worms. They are not gregarious, however. 



Aji investigation of the bionomics of this group of insects in relation 

 to cereal and forage crops in the central Great Plains was conducted 

 in Kansas. Sufficient supplementary observations were made in the 

 neighboring States to establish the applicability of the results. 



Information on the less important species of Phalaenidae, or owlet 

 moths, was also obtained. An extensive owlet moth fauna is present 

 in this region. Dining these investigations the larvae of 54 species 

 were observed in cereal and forage crops, pasture grasses, and 

 wastelands. 3 The following species are known to be of major eco- 

 nomic importance: Pale western cutworm (Agrotis orthogonia Morr.) ; 

 army cutworm (Chorizagrotis auxiliaris (Grote)); variegated cutworm 

 (Peridroma margaritosa (Haw.)) ; armyworm (Cirphis unipuncta 

 (Haw.)); fall armyworm (Laphygma frugiperda (A. and S.)); corn 

 earworm (Heliothis armigera (Hbn.)). 



Twenty-three additional species are of local or minor importance. 

 The remaining species were not known previously to be injurious to 

 cereal and forage crops. The species attacking these crops fall into 

 the following groups, based on the feeding habits of the larvae: 



Subterranean cutworms. — Species that feed almost exclusively beneath the 

 surface of the soil. 



Tunnel makers. — Species that make tunnels opening at the surface of the soil, 

 and, after cutting off portions of the host plant, drag their food into the tunnel 

 and consume it there. 



Surface feeders. — Species that feed at or near the surface of the soil. 



Climbers. — Species that have developed the habit of climbing the host plants 

 and feeding on the stems, buds, foliage, flowers, or seeds. 



Borers. — Species that bore into the stems or crowns of the host plants and feed 

 in the channels therein. 



FACTORS INFLUENCING DISTRIBUTION AND 

 ABUNDANCE 



The Phalaenidae discussed in this circular fall into two main groups 

 according to their moisture requirements. Cook (4, pp. 36-37) 4 

 pointed out that the distribution and abundance of the various species 

 and also the activities of their natural enemies are limited by the 

 moisture content of the soil and the seasonal sequence of this and other 

 ecological factors. 



Inasmuch as a portion of the central Great Plains lies within the 

 transition zone from semiarid to arid conditions, climatic fluctuations 

 would be expected to cause variations in the destructive range of the 

 phalaenid species inhabiting it. Thus, after a period of dry years 

 an eastward extension of the normal range of the pale western cutworm 

 was noted. The outbreak of this cutworm in western Kansas, which 

 began in 1936 and continued until 1941, was associated with the prev- 



3 The determinations of the various species of cutworms and their natural 

 enemies were made by specialists in the Division of Insect Identification, Bureau 

 of Entomology and Plant Quarantine, or by the writer by comparison with 

 specimens so determined. 



4 Italic numbers in parentheses refer to Literature Cited, p. 49. 



