2 BULLETIN 78, U. S. DEPARTMENT OF AGRICULTURE. 



the tobacco Crambus, great difficulty has been encountered, in 

 many of the experiments, in getting the perfect stand of plants so 

 essential for comparative tests. This led to a study of the life his- 

 ton T of the insect and of the somewhat extensive cultural experi- 

 ments by the Bureau of Entomology aimed at its control. The 

 effect of certain crop rotations in reducing injury from the tobacco 

 Crambus was noticed during the early progress of the cultural in- 

 vestigations b}^ Mr. E. H. Mathewson, Crop Technologist of the 

 Bureau of Plant Industry, to whom the writer is indebted for sug- 

 gestions concerning the cultural methods of control undertaken by 

 the Bureau of Entomology. 



GENERAL HABITS AND ECONOMIC IMPORTANCE OF THE GROUP 

 TO WHICH THE TOBACCO CRAMBUS BELONGS. 



The larva? of insects included in the family Crambidae, to which 

 the tobacco Crambus belongs, feed mainly on the grasses (Graminese), 

 although some of them subsist on plants of other families. Many 

 construct tubular, web-lined galleries near the roots of the plants on 

 which they feed, and some bore or tunnel into the roots or stems; for 

 this reason they have been named "root webworms." The moths, or 

 adults, are medium or rather small in size, with brown, yellow, or 

 white colors prevailing. Many species have metallic markings on 

 the forewings, which are comparatively long and usually narrow. 

 When at rest the forewings are rolled around the body and conceal 

 the hind wings, which are folded beneath. This gives the body the 

 appearance of a tiny cylinder, and accounts for the term "close- 

 wings." The species are widely distributed over the globe, but are 

 apparently most numerous in temperate climates. In North America 

 comparatively few are known, and the majority of these belong to 

 the genus Crambus, in which Dr. H. G. Dyar 1 catalogues 60 species. 



Moths of the genus Crambus fly mostly on dark afternoons and 

 during the early part of the night. They are more common in open 

 fields. When disturbed they make short erratic flights, rarely 

 flying more than a few rods at a time. They usually alight head 

 downward on the stems of plants, and their color often harmonizes 

 so perfectly with their surroundings that they can with difficulty be 

 seen. Most of the species are single-brooded; but as the moths of 

 different species emerge successively throughout the season, one or 

 more of the latter are present in most localities from spring until 

 late fall. Though various species of Crambus are common in most 

 localities, they seldom attract much attention unless some important 

 crop is attacked. This is due (1) to the fact that the moths are 

 small and inconspicuous, (2) to the underground feeding habits of 

 the arvse, land (3) to the fact that damage from different species is 

 distributed throughout the growing season. 



1 I>yar, Harrison G. A List of North American Lepidoptera * * *. U. S. Nat. Mus. Bui. .52, pp. 

 404-410, 1902. 



