46 BULLETIN 1374, U. S. DEPARTMENT OE AGRICULTURE 
These data show particularly the effect of pasturing after the stalks 
were cut. Between December 20 and 27, a herd of cattle was 
pastured in this field for a number of days. These cattle ate a 
considerable part of the bolls left on the surface of the soil. They 
picked up practically all the larger bolls, the sudden decrease in the 
number of larvae found per boll on December 27 being due to the 
removal of the larger bolls, which contained the greater number of 
larvae. Apparently there was no increase, or very little, in the 
number of larvae in the soil to offset the decrease in living larvae 
in bolls on the surface. The figures in the last column, giving the 
average number of the larvae in the soil that are found within locks 
or open bolls, before and after pasturing, show that there can not 
have been much trampling of bolls into the soil by the cattle. 
Early cleaning of fields in the fall, before a great part of the late 
unpickable bolls open, is recommended. In this way the number 
of bolls shed would be reduced. Grazing after cutting the stalks 
should be practiced, if possible, and it is possible that grazing before 
the stalks are cut is even more beneficial. If the stalks are not cut 
until all bolls are dry and open, it may even be advantageous to 
delay cutting until after cold weather has set in and the larvae have 
spun up more completely. Then possibly there might not be any 
appreciable issuance of larvae from shed bolls and entrance into the 
soil, and consequent pasturing would destroy a great part of the 
larvae in the shed bolls. 
TREATMENT OF SEED BY HEAT 
Machines for killing the pink bollworm in seed by heat have been 
in use in Egypt for some years. The Egyptian seed is practically 
lintless, whereas that produced in Mexico and the United States is 
covered with lint. For this and other reasons it was necessary to 
devote considerable attention to methods of treating seed. 
Laboratory tests were made to determine the amount of heat 
required to kill the pink bollworm in cottonseed, and the amount 
of heat to which seed may be exposed without injury. The latter 
point was determined by tests conducted by the Federal Horti- 
cultural Board at College Station, Tex., where laboratory facilities 
for this work were furnished by the college. These tests were 
conducted ic February, 1921, with Texas seed. A Freas electric 
oven was used. 
THERMAL DEATH POINT 
The tests on the thermal death point were conducted at Tlahualilo, 
using a Freas oven also. At first several series of tests were conducted 
in which larvae in double cottonseed were used. The procedure 
followed was to bring the oven to the desired temperature, which 
was maintained by thermostatic control. The seed, arranged in a 
single layer on a sheet of perforated cardboard, was then introduced. 
All larvae upon removal from the seed were placed in pill boxes and 
kept under observation for several days. One hundred double seed 
were used in each test. 
In one series of tests the seed was heated in dry air, that is, the 
normal air in the oven. In another series dishes containing water 
were placed in the oven. Evaporation from this water brought 
about a moist condition of the air. 
