30 THE CHINCH BUG. 
exceptionable for from one to two mouths. It is not unlikely, however, that wet 
weather may have the effect to stimulate the development of this parasite, either di- 
rectly or indirectly — a hypothesis which will reconcile all the facts now known, as 
well as the conflicting explanations of them which have been hitherto put forth. 
Assuming the dry weather abundance and wet weather scarcity of the 
Chinch Bag' to be proven, Dr. Thomas in 1880 published an elaborate 
article in which by a comparison of the rain-fall for forty years, with the 
destructive appearances of the insect for the same period, he not only 
established a definite relation between them, but upon an admittedly 
somewhat uncertain septennary periodicity of rain-fall advanced the fol- 
lowing practical conclusions : 
The first and very important practical fact revealed is that we may expect at 
most but two chinch bug years In every seven, with the strong probability, amount- 
ing almost to a certainty, that there will not be two in succession. As heretofore 
stated, two successive dry years are necessary in order to develop this species in ex- 
cessive numbers; the rain-fall records seldom show three dry years in succession, hence 
the chinch bugs are not likely to appear in injurious numbers in two successive years. 
The years 1854 and lb55 may, perhaps, form au exception to this rule. It is possible 
that the second brood of the first year may be sufficient to excite alarm, but experi- 
ence has shown that they do but little injury. We may, perhaps, with safety assume, 
as a general rule subject to occasional exceptions, that they will not appear more 
than once in excessive numbers during auy of the septennary periods. 
If the facts shown in reference to periodicity in our rain-fall are continued by future 
investigations, and this periodicity shown to be a meteorological law of the area in- 
dicated, the practical advantage of this knowledge to our farmers is apparent to every 
one. By this knowledge they will be enabled to predict with a reasonable degree of 
certainty wheu to expect these insects, and can rotate their crops so as to sutler the 
least possible injury. This knowledge will also enable them to dispense with precau- 
tionary measures except in such years as are likely to be followed by the appearance 
of the bugs. 
Experience has shown, and farmers are now becoming fully aware of the fact, that 
spring wheat and corn are the crops that chiefly aid in sustaining and developing 
this pest. Why corn should aid in this respect is easily seen, as it is the only exten- 
sive crop on which the second brood can feed. But why spring wheat should aid 
more in developing them than winter wheat is uot so easily explained, but that such 
is the fact must be admitted. It may possibly be accounted for on the presumption 
that the climate of the spring wheat region is more congeuial to them than that of 
the winter wheat area. 
These facts, combined with a knowledge of the time when tbe dry seasons are to 
be expected, will enable the farmers to substitute other crops as far as possible in 
place of spring wheat and corn. Even if the conclusion in reference bo periodicity in 
rain-fall should prove erroneous, the fact that two successive dry years are necessary 
to develop this species in excessive numbers will suffice to give notice at least one 
season in advance and allow the farmers to adapt their crops to the circumstances. 
When a dry season comes and an examination shows that the bngs are on the. increase, 
winter wheat, wherever it is possible to do so, should be substituted for spring wheat ; 
and oats, as far as possible, for corn. 
The uncertainty in reference to temperature will, perhaps, always prevent as from 
predicting with certainty that a coming year will be marked by the appearance of 
these insects, but we may say with assurance that a wet year will not bo followed by 
a chinch-bug year. Although this i9 not all we desire to know in this respect, it is, 
nevertheless, a very important fact and may be used to manifest advantage by our 
agriculturists. 
