W2 REPORT OF THE COMMISSIONER OF AGRICULTURE. 
showers for more than a week,” when there would be considerable 
cloudy weather and the atmosphere on the whole would be moist. 
Professor Riley has mentioned the fact that the larve and pupz 
are more readily killed by the wet weather than the adult insects, 
but that the latter are also killed. 
Mr. Walsh (Am, Ent., I, 175, 1869) gives the emphasis of italics to 
the following sentence: ‘‘In a hot, dry season Chinch-bugs are al- 
ways the worst ; in a wet season it is impossible for them to do any 
considerable amount of damage.” Dr. Shimer (loc. cit.) in his ac- 
count of the epidemic argued that it was doubtless the indirect effect 
of the wet weather. Dr. Thomas (Bull. 5, U. 8. E. C.) expressed the 
- opinion that the wet weather gave rise to a minute fungus which is 
the direct cause of the death of the insect. 
Professor Forbes says: ‘‘ The phenomena connected with the action 
of parasites which I have above described were apparently inde- 
pendent of any appreciable general cause, as they were most man- 
ifest at a time when the weather had been warm, dry, and altogether 
unexceptionable for from one to two months. It is not unlikely, 
however, that wet weather may have the effect to stimulate the de- 
velopment of this parasite, either directly or indirectly—a hypothesis 
which will reconcile all the facts now known, as well as the conflict- 
_ing explanations of them which have been hitherto put forth.” 
Assuming the dry weather abundance and wet weather scarcity of 
the Chinch Bug 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 appearance of the insect for the same 
period, he not only established a definite relation between them, 
but upon an admittedly somewhat uncertain septenary periodicity 
of rainfall advanced the following 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 
excessive 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 succes- 
sive years. The years 1854 and 1855 may, perhaps, form an exception to this rule. 
It is possible that the second brood of the first year may be sufficient to excite alarm, 
but experience 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 any of the septenary periods. 
If the facts shown in reference to periodicity in our rain-fall are confirmed by 
future investigations, and this periodicity shown to be a meteorological law of the 
area indicated, 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 when to expect these insects, and can rotate their crops so as to 
suffer the least possible injury. This knowledge will also enable them to dispense 
with precautionary 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 develop- 
ing this pest. Why corn shouid aid in this respect is easily seen, as it is the only 
extensive crop on which the second brood can feed. But whyspring wheat should 
aid more in developing them than winter wheat is not so easily explained, but that 
such is the fact must be admitted. It may possibly be accounted for on the pre- 
sumption that the climate of the spring-wheat region is more congenial to them than 
that of the winter-wheat area. 
These facts, combined with a knowledge of the tirae when the 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 to periodicity 
in rain-fall should prove erroneous, the fact that two successive dry years are neces- 
sary to develop this species in excessive numbers will suffice to give notice at least 
