30 
The corn acreage does not vary in Southern Illinois, as com¬ 
pared with our grades of total damage, in a way to make it worth 
discussing. 
Diagram III. The diagram of total injury for Central Illinois 
(HI.) conveys some extremely interesting and useful information, es¬ 
pecially with respect to the relation of oats culture to the chinch bug. 
The average wheat acreage makes, on the whole, a rapid rise as 
the total loss by chinch bugs increases (line A); while the corre¬ 
sponding average for oats (line B) decreases at first,—that is where 
chinch bugs are less numerous,—but increases for the higher grades 
of loss,—where the bugs are more abundant. Otherwise stated, in 
those townships of Central Illinois where the chinch bug is in¬ 
jurious but has not yet become destructive, its numbers vary di¬ 
rectly with the acreage of wheat and inversely with that of oats; 
but in those townships where it has become very abundant, it has 
already begun to breed in oats, and thenceforth its multiplication 
is stimulated by an increased oats acreage not less than by 
an increased area in wheat. We have here fully developed the 
fact barely noticeable in Diagrams I. and II., that where this in¬ 
sect injury is not yet great, it will, as a rule, be heaviest where 
there is most wheat and least oats, but that where it becomes 
severe, oats and wheat combine to increase its severity. 
The corn and grass figures of the tables from which Diagram 
III. was drawn are too variable to have any significance, and hence 
have not been diagramed. 
Diagram IV. The same may be said for that for Northern 
Illinois, only the column for wheat (Diagram IV.) having any 
particular meaning; and even here the ascending slope of the line 
for wheat is but slight. Still, it is to be noticed that the 
wheat area in the northern districts most injured by the chinch 
bug, was twenty-five per cent, greater, on an average, than in 
those not injured at all. 
Diagrams V. and VI. Finally, for a concluding summary of 
all the diagrams and tables for 1887, we turn to diagrams V. and 
VI., showing the acreage in each crop for the whole State, corre¬ 
sponding to the various degrees of total chinch-bug damage. The 
larger number of observations here included obliterates many of the 
more prominent irregularities of the other diagrams, and brings out 
without complication the main features of a broad general con¬ 
clusion. We see repeated here the marked contrast of conditions 
between Central and Southern Illinois (due, as already often ex¬ 
plained, to the widely different stage of insect increase): the rapid 
rise of the wheat line (V., B.) and the slower falling away of the line 
for oats (V., A.) for the lower grades of injury; the rapid rise of the 
latter line and the slower falling of that for wdieat for the higher 
grades,—the upward turn in the oats line being made a little in 
advance of the downward turn of that for wheat; the similar but 
less marked contrast between the lines for corn and grass (Dia- 
