106 



among the leaves of the cottonwood and the Carolina poplar. It is 

 noteworthy that I have made these observations at Urbana, Illinois, 

 upon cottonwoods growing upon what was originally prairie. 



Forbes ('07a) has shown, as the result of extensive collections of 

 May-beetles from trees, that they have a decided preference for Caro- 

 lina poplar (p. 456) and willow. This same paper also contains im- 

 portant observations on the nocturnal flights to and from the forest, 

 from the normal habitat of the grubs, and from the daytime abode of 

 the beetles in the open fields. Wolcott ('14) has recently emphasized 

 the point that the grubs live only in open places in proximity to wood- 

 land where the beetles can secure food. These observations show very 

 clearly that May-beetles are animals primarily of the prairie or forest 

 margin, and probably lived upon the original prairie, scattered, where 

 cottonwoods or willows grew. A glance at the map of the prairie and 

 forest (frontispiece) shows that the marginal area was very extensive, 

 and must have furnished an optimum habitat for these beetles. This is 

 a good illustration of the fact that the cottonwood exerted an influence 

 upon the prairie far beyond its shadow. 



In some localities another beetle (Melasoma scripta Fabr.) feeds 

 upon the leaves of the cottonwood, and may become a serious pest to 

 poplars and willows, but I have not seen this species abundant on iso- 

 lated mature trees upon the prairie. I have taken these beetles (July 

 2) under cottonwoods at Bloomington, 111. Packard ('90, pp. 426- 

 474) has published a list of the insects known to feed upon Popuhis. 



Willows (Salix) are frequently associated with the cottonwoods 

 upon the prairie, but, in marked contrast with these, they generally 

 grow in colonies and are eaten by a great variety of insects. Packard 

 ('90, pp. 557-600) lists 186 species of insects on them, and Chitten- 

 den ('04, p. 63) extends the number to 380 species. Of course in any 

 given locality the number of species found will be relatively small, and 

 the number is further limited by the environmental conditions — 

 whether the land is upland or low and flooded. The degree of prox- 

 imitv of willows and cottonwood is likely to influence the relative 

 abundance of the insects feeding upon these trees, since a large number 

 of insects which feed upon willow also feed upon the cottonwood. Col- 

 onies of willow are thus likely to become sources of infestation for 

 the cottonwood; this relation, however, is a mutual one. Walsh ('64) 

 and Heindel ('05) have published very interesting studies of the com- 

 munity life of the insect galls on Illinois willows. Cockerell ('97, pp. 

 770-771) has listed the scale insects found upon willows and poplars. 



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