84 



of my field assistants gave us a list of forty counties dangerously in- 

 fested, twenty-five of them over virtually their whole area. (Map 5.) 



As a matter of fact, by the first week in May of 1915 chinch-bugs 

 were reported dangerously abundant in wheat over the whole or nearly 

 the whole of the following twenty-nine counties, — Adams, Brown, 

 Cass, Menard, Pike, Scott, Morgan, Sangamon, Macon, Calhoun. 

 Greene, Jersey, Macoupin, Montgomery, Christian, Moultrie, Shelby. 

 Madison, Bond, Fayette, Effingham, St. Clair, Clinton, Marion, Mon- 

 roe, Washington, Jefferson, Randolph, and Perry, and in parts of the 

 following eleven others, — Mason, Schuyler, Fulton, Logan, Piatt. 

 Douglas, Coles, Cumberland, Jasper, Clay, and Wayne (Map 6). Ex- 

 traordinarily heavy beating rains in May and June so far reduced the 

 numbers of the insects that by the 20th of June, 1915, all danger of 

 aii outbreak was over for the year and the office force organized for a 

 field campaign was called in and broken up. 



Local and General Causes of the Outbreak 



The original causes of the outbreak we are studying, of its con- 

 tinued increase for six successive years, of its extension northward 

 and its restriction and even retreat in the south and east, and those of 

 its final disappearance, are to be ascertained only by careful inquiry 

 into the conditions by which it was preceded, in the midst of which it 

 arose, under which it was maintained, and by which it w T as surrounded. 

 Such an inquiry must of course take into account all that we definitely 

 know or may intelligently surmise concerning the effects of weather, 

 soil, crops, parasites, predaceous enemies, and contagious diseases upon 

 the rate of insect multiplication. 



The weather relation may be very briefly described. Unusually warm 

 weather, continued thru each year 's breeding season of the bugs — that 

 is, from May to August inclusive — and the absence of heavy beating 

 rains during this period of the hatching and growth of the young, es- 

 pecially during June and August, are conditions generally regarded 

 as favorable to a high rate of increase ; while weather cooler than nor- 

 mal during the late spring and summer, accompanied by an abundance 

 of rain falling in beating storms in late May, June, and August, but 

 especially in June, may put an end to a destructive outbreak in a sin- 

 gle year. The crop relation may be described with equal brevity. Fav- 

 orable weather conditions will take first effect, other things being ap- 

 proximately equal, in an area where the crops are most largely those 

 upon which the chinch-bug can maintain itself — that is, the cereal 

 crops and the forage grasses — and where those crops are so massed 

 and so distributed that the bugs can easily find their way to wheat in 

 spring and to oats and corn at and soon after the time of the wheat 

 harvest. It is also commonly believed that an outbreak is most likely 

 to appear in Illinois where a sufficient acreage of winter wheat is so 



