93 



As a general conclusion from the foregoing discussion we may say- 

 that our outbreak made its start in the wheat-growing counties under 

 conditions of high spring and summer temperatures for two succes- 

 sive seasons, but with no marked deficiency of rainfall ; that it spread 

 thence by a process of overflow in the direction of the prevailing winds 

 at the times of the dispersal flights of the bugs, and into wheat-growing 

 counties to the virtual exclusion of those in which wheat was not an im- 

 portant crop ; that it reached its most destructive abundance in wheat 

 country to the northward of its place of origin ; and that it was 

 finally swept in this direction into areas where wheat is decidedly 

 secondary to corn, hay, and pasture grasses, doing there a diminished 

 damage, however, except to corn which grew beside infested fields of 

 wheat. 



It must be admitted, however, that proof of the immediate de- 

 pendence of chinch-bug increase on high summer temperatures and 

 moderate rainfall and upon the character of the agricultural crops, 

 is not here so clean-cut and positive as to put these conclusions alto- 

 gether beyond question. A great chinch-bug outbreak is, as a rule, 

 general over a wide territory — the present one, for example, covering 

 the greater part of Oklahoma, Kansas, and Missouri, besides some 

 forty counties in Illinois. It began, indeed, earlier in the West than 

 in Illinois itself, chinch-bugs being destructive there in the spring of 

 1907, more than two years before our first observation of its preva- 

 lence in this state. The occurrence and maintenance, for a term of 

 years, of any uniform weather conditions over so great an area seems 

 quite improbable ; and the problem is one which should at any rate 

 be studied over the entire territory of an outbreak as a unit rather 

 than in a fragment of it on its margin. Furthermore, all our conclu- 

 sions are based on field observations only, and are wanting in the 

 precision and conclusive character of experimental investigation. Just 

 how varying temperatures affect the chinch-bug; at which degree of 

 heat it becomes active ; how high a temperature is most advantageous 

 to it, and at what degree is begins to suffer ; how long a season is most 

 conducive to its rapid multiplication ; and what are the effects upon it 

 of different degrees of humidity at varying temperatures, — these arc 

 all questions which must be answered before a complete solution of 

 the problem of meteorological relations can be reached. 



The sensitiveness of the chinch-bug to differences of temperature 

 is well shown by its habits in the field when it is attempting to escape 

 from the dried-up stubble after harvest. It does not ordinarily begin 

 its movements in the forenoon until the weather of the day warms up 

 to about 74 degrees F.,* and on hot bright days its activities cease in 



*Upon this point the following field-notes by Mr. Flint for the summer of 

 1912 have an interesting bearing: 



"The temperature at which chinch-bugs, assembled just within the road-oil 

 Hue, begin to move in the forenoon was noticed on several days. They were never 

 seen in motion when the thermometer was below 74 degrees I 1 ., and no effort to es- 



