Distribution of the Alfalfa Weevil 
491 
Climatic conditions in America were 
analyzed to determine the areas of 
optimum and limiting conditions, 
which have been charted and compared 
with the present distribution of the 
alfalfa weevil. They have been found 
to correspond in all essential particu¬ 
lars with the progress of the present 
infestation. 
It seems highly probable that the 
alfalfa weevil has been imported into 
this country many times and that it 
also has often been shipped out of the 
quarantined areas into other parts of 
the country, but that it has failed to 
establish itself except where it was 
placed in a region of favorable climatic 
conditions. 
The climatic limitations of other in¬ 
sects are different, for every insect has 
its own definite optimum" and limit¬ 
ing factors. Some insects, like the San 
Jose scale and the brown-tail moth 
( 11 ) are definitely limited on the north 
by minimum temperatures. Others re¬ 
quire a certain length of growing season. 
Still others, chiefly boreal forms, can 
endure intense cold but succumb to 
heat and have a definite southern limit. 
With regard to rainfall, - the same is 
true. Insects like the army worm and 
the variegated cutworm require a 
humid condition, and others like the 
pale western cutworm require a dry 
condition. It seems highly probable 
that there are one or more periods in 
the life of arty insect when it is especially 
susceptible to unfavorable climatic con¬ 
ditions. If these periods can be found, 
and their climatic optima and limits 
determined, the range of the insect can 
be mapped. In the case of the alfalfa 
weevil the limiting periods are two in 
number—the temperature limit, which 
applies largely to the hibernating 
adults, and the humidity limit, which 
applies to the larva and its fungous 
enemies. 
The method of climatic analysis used 
in this paper has been applied success¬ 
fully to an insect inhabiting the soil 
(the pale western cutworm ( 2 )) and to 
an insect feeding on the aerial portions 
of low plants (the alfalfa weevil). In 
order to determine the applicability of 
the method to insects in general, it 
remains to apply it to some insect 
living in trees. The forest environ¬ 
ment, either natural or in a cultivated 
orchard or grove, is, widely different 
from conditions in the open, and the 
problem must be attacked by an 
analysis of actual forest conditions, 
after which these conditions must be 
correlated with the available weather 
data from near-by stations. For this 
reason the method will probably need 
considerable modification before" it will 
apply to forest insects. 
LITERATURE CITED 
(1) Ball, E. D. 
1917. [DISTRIBUTION of alfalfa weevil in 
UTAH]. Bien. Rpt. State Hort. Com. Utah 
1914-16: 144-145. 
(2) Cook, W. C. 
1924. THE DISTRIBUTION OF THE PALE WESTERN 
CUTWORM, POROSAGROTIS ORTHOGONIA MORR: 
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69, illus. 
(3) Hann, J. 
1908-11. handbuchder klimatologie. Aufl. 3, 
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(4) Kendrew, W. O.' 
1922. THE CLIMATES OF THE CONTINENTS. 387 p., 
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(5) Kincer, j. B. 
,1919. THE SEASONAL DISTRIBUTION OF PRECIPITA¬ 
TION AND ITS FREIUENCY AND INTENSITY IN 
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(7) Parks, T. H. 
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POSITION OF THE ALFALFA WEEVIL (PHYTONO- 
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(8) Reeves, G. 1. 
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(9) -- and others. 
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(10) ROCKWOOD, L. P. 
1916. SPOROTRICHUM GLOBULIFERUM SPEG., A 
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(11) Sanderson, E. D. 
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(13) - 
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o 
