-3^ 
EXTENT OF SURVEY 
As in 1936, the districts surveyed were restricted to those 
considered most important in regard to alfalfa culture and weevil 
damage. Twelve districts were sampled, and these included portions 
of Oregon, Idaho, Utah, Colorado, Nevada, aid Nebraska. 
METHODS 
The sampling plan was the same as that followed in 193&, * 
representative square-foot samples "being taken from each of 25 fields 
in a district, except in the smaller districts, where 12 fields were 
considered sufficient. Such sampling does not give highly accurate 
estimates for individual fields "but provides a useful indication of 
the general level of weevil abundance in a district. 
Each sample was taken by forcing into the soil a metal die 1 
foot square and removing all alfalfa crowns, litter, and weeds en- 
closed by the die, as well as the soil from the enclosed area to a 
depth of from 1 to. 2 inches. Later, each sample was reduced in volume 
by washing, so that its content of weevils, parasite cocoons, and 
litter remained in the lower of two screen-bottom tubs. These washed 
samples were individually wrapped in absorbent-paper towels to remove 
excess moisture and were examined in the laboratory on a white porce- 
lain tray. 
LIMITATIONS ON USE OE DATA 
Obviously no forecast of weevil damage (or parasite effective- 
ness) can be exact. Nevertheless it is believed that considerable loss 
can be averted if interested State entomological workers and county 
agricultural agents will watch developments in those localities in which 
the survey has indicated a prospect of important damage by the alfalfa 
weevil. Our interpretation of survey data is based on the generality 
that an average population of two adult weevils per square foot is neces- 
sary to produce economic damage in most of the older weevil-infested 
territory. However, the outlook gained from surveys made in the fall is 
subject to modification by mortality of adult weevils during the winter. 
Also, the amount of damage in any locality depends on whether spring 
weather favors or hinders weevil development. Again, certain field con- 
ditions manifested by thin stands or poor growth may aggravate the 
damage in any field or in any district where these conditions prevail, 
because fewer adult weevils are- required to create a larval concentration 
sufficient to cause. damage. Finally, injury in any field populated by a 
menacing number of larvae is increased by delay in harvesting after the 
plants are mature. Such maturity is indicated by budding Of the top crop, 
together with scattered blossoms and appearance of the earliest basal 
shoots of the succeeding crop. 
