338 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1942 



able conditions. The interactions among these pests, their insect 

 enemies, their diseases, and the weather, are extremely complex. 



Since we have not yet learned to control the weather, which is the 

 dominant element in this combination, we are not able to manipulate 

 these factors to any material extent in the prevention of insect out- 

 breaks. In fact, some of our grain-production practices have been 

 more favorable then detrimental to such outbreaks. For example, the 

 planting of large acreages of both corn and small grains in the same 

 neighborhood encourages the multiplication of the chinch bug, as al- 

 ready cited. Another example is the favorable condition for grass- 

 hoppers brought about, partially at least, by the extensive growing of 

 wheat during the first World War. With the urgent demand for that 

 grain, great areas of virgin sod on the western plains were plowed and 

 sown to wheat. Although much of this land was gTadually abandoned 

 as the demand for wheat subsided, both the wheat stubble and the aban- 

 doned land have i)rovided extremely favorable food and egg-laying 

 conditions for the migratoiy grasshopper, and have been important 

 factors in the persistence and severity of the widespread and almost 

 coiitinuous grasshopper outbreaks in the Great Plains during the past 

 decade. Fortunately, it has been possible to prevent a large portion of 

 the potential crop damage through the application, at great expense, of 

 the baiting method already described, but the problem of working out 

 and applying methods of preventing the outbreaks themselves still 

 remains. This problem can undoubtedly be solved, possibly through 

 the use of some of the slower airplanes for spreading poison bait, when 

 they become available for other than war purposes. 



Many of the insect pests of cereal crops, like most of the crops them- 

 selves, are not native to this country. Others have adopted these crops 

 as food when they have become widely grown in this country. Notable 

 examples of foreign invaders are the hessian fly, European corn borer, 

 and most of the insects that attack our stored grains and cereal prod- 

 ucts. The armyworm, chinch bug, and green bug might be mentioned 

 as conspicuous among native insects that have taken readily to im- 

 ported crops. In cases where the parasite enemies of the invaders did 

 not come along with them efforts have been made to import and estab- 

 lish these parasites. Some of these have become well established while 

 others apparently have not found conditions in this country at all to 

 their liking. In general, it may be said that although the parasites 

 of insects attacking cereal crops are highly beneficial, in no case can 

 they be depended on to keep these pests under permanent control. 

 Other means must therefore be found and applied when necessary if 

 the cereal crops are to be successfully and profitably grown, stored, 

 milled, and supplied to the human rather than the insect population 

 for consumption. 



