6 BULLETIN 808, U. S. DEPARTMENT OF AGRICULTURE. 



practically every wheat-growing section east of the Mississippi 

 Elver, it rarely lias caused any serious losses in recent years, al- 

 though it exacts a small toll annually. This possibly may be ex- 

 plained by the fact that wheat fields in the Eastern States are lo- 

 cated usually at a distance from the old stubble fields of the previ- 

 ous, year, and since the spring generation is wingless, only a small 

 percentage of the individuals is able to make the journey safely 

 from one wheat field to another, and it thus becomes difficult for the 

 species to maintain itself. 



H. grandis is a comparatively old offender, but probably has 

 escaped being confused with other species, as it has some rather 

 striking characters, though the fact that it is dimorphic greatly 

 jDerplexed all entomologists for a number of years. Each form was 

 considered and described as a separate and distinct species. Riley 

 (11) described the spring form as Isosoma tritici 

 in 1882, since he considered Fitch's tritici as a 

 synonym of hordei Harris. In 1884 the late F. M. 

 Webster established the dimorphic habits of 

 grandis^ rearing both forms, and Riley (12) de- 

 scribed the summer form as Isosoma grande. In 

 1896 Howard (8, p. 10) definitely established 

 Fitch's tritici as a valid species and gave the 

 name minutum, to the vernal generation of Riley's 

 species previously referred to in literature as 

 tritici. H. grandis is probably the most inter- 

 esting species of the whole group. There is one 

 other species that has two generations during the 

 year, but no others, so far as is known, are 



dimorphic. 



Fig. 3. — Wheat straw- 

 worm : Wingless adult 

 female of spring form 



(EarmoKta grandis, HOST plants. 



t o r m mi n ut a ). 

 CTi*G3,tlv pulstrsTGcl __ 



(Webster and The Writer has never succeeded in rearing H. 



Reeves.) grcmdis from any plant but wheat. He has 



observed it oviposit in other plants but no larvae were ever found 

 in them. Further experiments along this line may disclose other 

 hosts. As it is found in sections where very little wheat is grown 

 consecutively, it seems as though there must be at least one other 

 host. 



LIFE HISTORY AND MANNER OF INJURY. 



The spring .form (fig. 3) {H. grandis, form minuta) attacks the 

 wheat plants when they are small (fig. 4), the eggs (fig. 2, /) being 

 deposited in the base of the young plant. The developing larva 

 totally destroys the tiller affected, and if the plant has not tillered 



