Mar. 1,1926 
Distribution of the Alfalfa Weevil 
487 ' 
SUITABILITY OF AMERICAN CLI¬ 
MATE FOR THE ALFALFA WEEVIL 
Rainfall 
Students of American climatology 
recognize several types of rainfall dis¬ 
tribution. Ward { 17 ) lists 14 rainfall 
types, but for our purpose there are 6 
main types, as designated by Kincer 
( 5 ), fahich he calls the Florida, East¬ 
ern, Plains, Arizona, sub-Pacific, and 
Pacific types. 
Of these 6 types the summer rain¬ 
fall is less than 6 inches in four types 
Pacific type has a very pronounced 
winter maximum, with almost rainless 
summers. The sub-Pacific type, illus¬ 
trated by Salt Lake City (fig. 8), has no 
pronounced winter maximum, but fairljf* 
heavy rainfall occurs from March to 
May. Farther north in Idaho there is 
a more pronounced winter maximum, 
with a secondary maximum in May. 
(Payette, fig. 9.) In western Colorado 
the-rainfall is very light with no pro¬ 
nounced maximum. (Delta, fig. 10.) 
The weevil is apparently excluded 
from most of America east of the 
Rocky Mountains by abundant spring 
lL 
-f 
/nr //. 
9(/<r. 
SEP? rl 
0 
cr 
>/j wr 
M 
prtMP. 
/ 
z* 
OPE 
6 
w 
W/VUMJ. 
: TEMP 
jr/S'E 
S9//N 
M „ .1 - 
J_ 
t - 
' 62 * 
1 
Fig. 8.—Climograph for Salt Lake City, Utah 
and less than 4 inches in two of these. 
The Plains type is characterized by a 
summer maximum, the summer rain¬ 
fall ranging up to 12 inches or more. 
However, there are certain parts of the 
plains, on the eastern slope of the 
Rockies, in which the summer rainfall 
is from 4 to 6 inches, and it is in these 
places that the weevil may possibly 
occur. The Arizona rainfall type is 
characterized by a late summer maxi¬ 
mum in July and August, but there are 
some regions in this type In which the 
summer rainfall is very small. The 
and summer rainfall. It would appear 
to be limited to such districts west of 
the Rockies as have favorable temper¬ 
ature conditions and to a small area 
lying immediately east of the Rockies, 
which has scanty summer rainfall. 
Temperature 
Within the rainfall regions outlined 
above the distribution and abundance 
of the weevil are controlled by temper¬ 
ature. Regions having a mean annual 
temperature of 50° F. or higher ap¬ 
proach the optimum. When this tern- 
