April/ 15] 



SHELFORD: ORIGINAL INSECT HABITATS 



171 



SUGGESTIONS AS TO THE ORIGINAL HABITAT AND DIS- 

 TRIBUTION OF VARIOUS NATIVE INSECT PESTS 



By V. E. Shelford, University of Illinois 



I. Introduction. — Before Eastern North America was put under 

 agricultural conditions it was densely covered with forest west to the 

 Illinois and ^Mississippi Riv^ers, and with conifers to the north, Fig. 10. 

 Along the western border of the forest was a belt of prairie or savanna 

 which consisted of groves of forest, stream skirting forest, interspersed 

 vriih. moist grassland. To the west of this were the arid plains along 

 the rivers of which was moist area vegetation. Considering the for- 

 ested portion of this we cannot too much emphasize the fact that it 

 was continuous forest entirely different from the present open aspect. 

 The forest was broken in the eastern portion by rivers and marshes 

 and sand dunes of the lakes and coast, which formed an insignificant 

 portion of the entire area. In addition to this there were small 

 'islands" of moist prairie scattered eastward north of the Ohio River 

 as far as central Ohio. 



Scarcely any of the pests of forage or garden crops are forest animals, 

 and only a few orchard and small fruit pests are strictly so. When we 

 consider that these pests have made their way in Eastern North 

 America at least, on to planted crops where ever and as fast as these 

 have been put out, we must explain their presence either by assuming a 

 rapid migration with the development of agriculture and the clearing 

 of the land, or we must assume that these animals were present 

 through-out the forest area before agriculture was introduced. 

 While som.e species have migrated beyond doubt, others have in all 

 probability notd one so. 



II. The Original Habitat of Native Pests. — A close study of the 

 habitat preference of various insects appears to throw much light upon 

 the original habitat of a great many native pests. Taking first the 

 insects which frequent garden and forage crops and which are widely 

 distributed, an inquiry into their habitat shows that they fall into two 

 classes, (a) those frequenting low moist situations, and (6) those pre- 

 ferring higher and drier ground. An examination of the fragments of 

 primeval vegetation likely to support such insects shows that the mois- 

 ter situation frequenting species are found along the margins of ponds, 

 (PI. 7, fig. 1), lakes, rivers and even on the vegetation growing in the 

 water, and on marsh meadows or grassy areas covered by water in 

 spring but dry in summer. 



Taking Sanderson's recent work on insect pests and Forbes' report 

 on the insects of the Indian corn plant and comparing them with lists 



