13G REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
firm in a marked or distinct manner the theory that heat and dryness 
are absolutely necessary to an excessive development of locusts. But 
we think the investigation is not without profit, first, because it shows 
that a longer series of years is necessary to determine satisfactorily the 
relation between meteorological conditions and the locust development; 
second, because it shows that annual and monthly means, so far as tem- 
perature is concerned, are of but little value in the solution of this 
question; third, because it indicates the necessity of paying more atten- 
tion to the temperature in winter, in reference to this question, than we 
have been disposed to allow; fourth, because it presents some facts 
which indicate the necessity of somewhat modifying the theory advanced 
in our First Report, and maintained in the previous part of this chapter. 
We have assumed in our First Report, as well as the present, that as a 
very general rule the locust swarms that invade Nebraska, Iowa, and 
Kansas come directly from their native breeding-grounds in British 
America, Montana, and Western Dakota. Now, several facts presented 
by the meteorological data agree better with the idea that two seasons 
at least are required for this purpose ; that is, that those developed by 
a favorable season in these northern regions migrate that season to 
Southern Dakota and Northern Nebraska, and, if the next season is 
favorable in this region, move farther south in increased numbers; if 
the season is unfavorable they proceed no farther, or in very diminished 
numbers. The temperature and rainfall in 18C2-'G3, and 1872-73, 
appear to accord bettor with this theory than the other. 
Be this as it may, we have given the facts as we find them, that those 
who desire to investigate the subject may have the data at hand prop- 
erly arranged so as to show their bearing upon the question. We confess 
our disappointment in the result of our attempt to prove a theory so 
long maintained, and so universally believed ; but, as before stated, we 
are unwilling to abandon it, notwithstanding the meteorological records 
fail to confirm it in the marked manner we expected, for personal expe- 
rience and observation have too often confirmed it. 
There is still another way in which the relation of temperal ore to the 
development of the locusts may be viewed which does not appear to 
have been brought forward until touched upon in our First Report. 
Professor Cleveland Abbe, of the Signal Service Bureau, has suggested 
the idea that the development of the eggs may depend upon the sum of 
the heat rather than the degree ; that is to say, the number of hours they 
are subject to heat above a certain degree. This opinion impressed it- 
self very favorably upon our minds, and the ingenious method adopted 
by the Professor to demonstrante it, as given in our First Report 206 
agreed so well with the facts that we were disposed to accept it as the 
true key to the relation between temperature and locust development. 
Without at present deciding as to its value we must confess that a more 
thorough examination of it has tended to render us somewhat skeptical as 
to the value of the theory when applied to the data in solving the pr'ob- 
™ Tages 425-432. 
