NON-PEOTOZOAN FAUNA OF SOIL 361 



varied from 4.88 per cent for the Myriapoda to 11.18 per cent for the 

 Collembola, making a total nitrogen content of the fauna of an acre of 

 manured ground 16.2 pounds and 7.5 pounds for unmanured ground. 

 More than half of this nitrogen was in the bodies of the earthworms. The 

 action of worms and insects in assisting the breaking down of vegetable 

 matter, with the formation of amorphous "humus," was considered 56 

 of importance. The soil insects are frequently classified 57 into three 

 groups: beneficial, noxious and innocuous. The first include such 

 forms as species of Ichneumonidae and Braconidae, which are parasitic 

 on cutworms, predatory Carabidae and scavenging Scarabaeidae. 

 The noxious insects are found among the Elateridae, Noctuidae, some 

 Scarabaeidae, Curculionidae and Tipulidae. The innocuous forms 

 are those which find in the soil a temporary retreat for pupation ; even 

 injurious species, like the potato-beetle, may be harmless during the 

 soil phases. 



Among the most important insects whose larvae may become of 

 great economic importance in the soil in injuring field crops, are the 

 wireworms, white grubs and cutworms. 58 The parents of the wire- 

 worms are the so-called "click," "jumping" or "snapping" beetles. 

 The adults deposit their eggs chiefly in grass land. The small wire- 

 worms which hatch out feed on the roots of various plants or seeds 

 before they are sprouted, especially when the crop is planted after sod. 

 This continues until the insects are fully mature, which requires three to 

 five years. The damage is usually most severe in spring. An abun- 

 dance of wireworms in sandy soil frequently makes it necessary to 

 abandon or "rest" the land. 



The parents of the white grubs are the June bugs (beetles) which also 

 lay their eggs principally in sod land during June. The eggs hatch in 

 about two weeks. The grubs feed on any plants available and go down 

 seven to fourteen inches below the surface when cold weather approaches. 

 With the coming of warm weather the following spring, they come up 

 again towards the surface where they feed on plants throughout the 



' 6 Kostytschew, P. Russian tschernoziems. Pctrograd. 1886, p. 165-191. 

 Ann. Sci. Agr., 2: 1887; Recherches sur la formation et les qualites de l'humus. 

 Ann. Agron., 17: 17-38. 1891. 



47 Cameron, 1925 (p. 356). 



* 8 Headlee, T. J. Soil-infesting insects. N. J. Agr. Exp. Sta. Cir. 26; Ander- 

 son, G. M. The slender wireworm; its relation to soils. S. C. Agr. Exp. Sta. 

 Bui. 204. 1920; Thomas, W. A. Corn and cotton wireworms. S. C. Agr. Exp. 

 Sta. Bui. 155. 1911. 



