48 
of such species as produce but one or two generations in a year, 
as the Locust, Chinch-bug, Hessian-fly, Army-worm, etc. On the 
other hand the plant lice and other insects that produce a number 
of broods in a year are often developed in enormous numbers in a 
single season; yet it was the opinion of some close observers in 
England that the meteorological condition of one or two autumn 
months determined to a great extent the status of the Hop Aphis 
the following season. 
In the course of my entomological investigations, especially in 
studying the history and habits of the Chinch-bug and Western 
Locust, I have found the meteorological factor constantly appearing. 
I concluded, therefore, to make a more thorough examination of 
the influence of climatic conditions on the development of these 
species than had been heretofore done. The result in reference to 
the latter insect is not what was to be expected, and cannot be 
considered as satisfactory, but it is unnecessary for me to say more 
in regard to it, as Illinois does not suffer from the incursions of 
this pest. On the other hand, this attempt in the case of the 
Cliinch-bug has brought to light some new and interesting facts, 
which may ultimately be of use in aiding us to counteract its in¬ 
crease, and to a great degree prevent its injuries. 
For the purpose of this investigation I selected Illinois and the 
immediately adjoining portions of Iowa and Missouri, first, because 
the history 'of the species has been more thoroughly written up for 
this section than any other; and secondly, because the meteorologi¬ 
cal records, though incomplete, are fuller for this section than any 
other of the area infested by this pest. Confining my investigations 
to this section, excluding the Cairo record as not belonging to the 
same limited climatic type, and rejecting the early Sandwich record 
as doubtful, I have, for the purpose of ascertaining the rain precipi¬ 
tation, combined the rainfall records of the others and taken the 
average for each year. For the average from 1873 to 1877, I have 
used the Signal Service records of Chicago, Dubuque, Davenport, 
and St. Louis, counting the year from January to December, so as 
to correspond with the preceding portion of the series. 
This series commences in 1840 with the Athens record. 
For the temperature an average of different stations would fail to 
give a correct idea of the comparative annual or monthly means of 
different years, hence it was necessary to select as a standard a 
station as near the centre of the area as possible. 
For this purpose the record of the station at Augusta, Hancock 
county, Illinois, was chosen, and for two or three missing years the 
temperature is estimated from two or three of the nearest stations 
by ascertaining the difference between the general average of the 
series of each. 
The result is shown in the following tables: 
