328 ANlSrUAL REPORT SMITHSONIAN INSTITUTION, 1942 



the following spring, while fields that had been cleanly fallowed prior 

 to seeding escaped injury. 



Eotation with other crops is often used to great advantage in pre- 

 venting injury to cereal crops, especially by certain species with re- 

 stricted food habits. The larvae of June beetles, commonly called 

 white grubs (pi. 14), are partial to crops belonging to the grass family 

 and, by gnawing their roots, cause serious injury to pastures and grain 

 crops planted on land that has been in sod. Leguminous crops, on the 

 other hand, are unfavorable to their development, and the proper use 

 of legumes in the rotation, or in combination with grasses in pastures, 

 serves to reduce their depredations to negligible proportions. 



The corn rootworm (pi. 4) , a serious pest in the Corn Belt, and the 

 grape colaspis, another enemy of both corn and soybeans in that region, 

 often become extremely abundant in fields that are planted to corn 

 or soybeans for 2 or 3 years in succession. These insects are very 

 restricted as to food plants, however, and can be readily eliminated 

 as serious factors by crop rotations that are not only effective for this 

 purpose but also are good general farm practices. 



Suitable crop rotations are also very useful as auxiliary preventive 

 measures against several insects such as the hessian fly, strawworm, 

 jointworm, and sawfly, which frequently cause serious injury to 

 wheat. 



Crop rotations and intensive farming, on the other hand, may be 

 favorable to some insects, such as the chinch bug (pi. 12). This is a 

 native American insect which probably fed on certain wild prairie 

 grasses and was of no consequence before the native sod was plowed 

 and planted to crops. The settlement of the prairies and the almost 

 complete utilization of large areas for the production of grains pro- 

 vided the chinch bug with crops much to its liking. An abundance 

 of wheat and other small grains for the early summer brood to feed 

 upon, and great acreages of corn in close proximity on which to finish 

 its growth and produce one or more additional broods during the 

 season, were ideal for its multiplication, with the result that it imme- 

 diately became and has since remained one of our worst grain pests. 

 Much can be done toward its control, however, by modifying the 

 farming system so as to break the continuous rotation and the prox- 

 imity of corn and small grains so favorable to the chinch bug, through 

 the use of leguminous crops and pastures. 



Other cultural measures inherent in good fann practices, such as 

 the use of fertilizers and soil-building crops, the planting of the new 

 crop as far away as possible from the fields that bore the same crop 

 the previous year, and the use of the best adapted and most vigorously 

 growing varieties are all helpful as auxiliary measures for the control 

 of cereal crop pests. Since most of these are, in themselves, profitable 



