THE DISTRIBUTION OF THE ALFALFA WEEVIL (PHY- 
TONOMUS POSTICUS GYLL. A STUDY IN PHYSICAL 
ECOLOGY 1 
By William C. Cook, 
Assistant Entomologist , Montana Agricultural Experiment Station 
INTRODUCTION 
The alfalfa weevil ( Phytonomus pos¬ 
ticus Gyllander) is a recently intro¬ 
duced insect which is doing a large 
amount of damage in the Great Basin 
region. It was first noted near Salt 
Lake City, Utah, in 1904, and has 
spread until up to the present time it 
has been captured in Oregon, Idaho, 
Wyoming, Colorado, Nevada, and 
California, as well as in Utah. In 
many parts of its present range it is 
capable of doing an immense amount 
of damage, at times almost completely 
destroying the alfalfa crop. Although 
the area now occupied by the insect is a 
small portion of the total area devoted 
to alfalfa growing in the United States, 
the insect is regarded with alarm by all 
of the neighboring States, which have 
enacted quarantine laws against al¬ 
falfa in an effort to retard the further 
dispersion of the weevil. 
At the present time the insect is 
rapidly spreading into new territory, 
and it would be a matter of great in¬ 
terest and value to determine, with 
some degree of accuracy, the probably 
final limits of its distribution in Amer¬ 
ica. This paper is an attempt to de¬ 
termine, from the climatic limitations 
found in Europe and Asia, the probable 
economic distribution of the alfalfa 
weevil in America. The study will be 
presented in three parts: (1)*A com¬ 
pilation of all known information con¬ 
cerning the effects of climatic factors 
on the life history and abundance of 
this species in America; (2) a study of 
its distribution in Eurasia, to deter¬ 
mine the optimum and limiting cli¬ 
matic conditions; and, (3) the applica¬ 
tion of this information to a study of 
climatic conditions in America, to lo¬ 
cate the regions of optimum and limit¬ 
ing conditions, and to outline the dis¬ 
tribution. 
CLIMATIC ECOLOGY OF PHYTONO¬ 
MUS POSTICUS IN AMERICA 
The data which are quoted in this 
portion of the paper have been taken 
from various papers on the alfalfa wee¬ 
vil, and the material has been quoted 
in full in each case, following the au¬ 
thority, which is placed in parentheses. 
Outline of Life History 
The alfalfa weevil winters in Utah 
as an adult in trash and weeds in fields. 
Early in the spring the adults emerge 
from hibernation and fly about actively, 
seeking a place for oviposition. This 
is known as the spring flight and occurs 
in April and early May. Oviposition 
continues into June, reaching a maxi¬ 
mum late in May. The majority of 
the larvae are found feeding on the al¬ 
falfa leaves in early June in Utah. 
They pupate in June, and the adults 
emerge in early July to feed and fly 
around for a month or so (summer 
flight), after which they appear to be¬ 
come much less active, finally hibernat¬ 
ing in the fall. There is only one com¬ 
plete generation per annum. In Utah 
there is sometimes a partial second 
generation, but the larvae do not sur¬ 
vive the winter. The larvae strip the 
leaves from the first crop of alfalfa, 
and after that is cut they keep down 
the sprouts of the second crop until 
late in June, so that this crop is greatly 
reduced, and the third crop is so late 
as to be of little value. 
Direct Relations of Climatic Fac¬ 
tors to the Life History 
TEMPERATURE 
Reeves et al. ( 9 , p. 91) 2 state: 
“ There is no definite hibernation in 
this species. The adults are quiet 
when it is cold and active when it is 
warm . ; 
Titus (14, p . 108), says: “The time 
of 'entering hibernation varies greatly 
in different years and in different local¬ 
ities. If the summer is long, with 
warm, sunshiny weather throughout 
the latter part of the season, the 
weevils enter hibernation late and 
many of them perish before the summer 
ends. On the other hand, if the late 
1 Received for publication June 11, 1924; issued May, 1925. 
2 Reference is made by number (italic) to “ Literature cited,” p. 492. 
Journal of Agricultural Research. 
Washington, D. C. 
( 479 ) 
Vol. XXX, No. 5 
Mar. 1, 1925, 
Key No., Mont. 12 
