December, ’20] THOMAS: COTTON worm 489 
A STUDY OF THE EFFECT OF COTTON WORM ON BOLL 
DEVELOPMENT AND COTTON YIELD 
By F. L. Thomas, Assistant Entomologist , Alabama Experiment Station 
During the summer and fall of 1919 the writer was engaged in carry¬ 
ing on cotton dusting experiments at Prattville, Ala., on the plantation 
of the McQueen Smith Farming Co. 
While examining cotton on selected plots during the first week of 
August several small caterpillars of the cotton worm moth were found. 
In four or five days the worms were very abundant and apparently in 
all stages of growth on cotton which had not been poisoned. By the 
11th of August the worms had begun to pupate. 
The cotton on this plantation had received a heavy application of 
ammonia fertilizer and the unusually wet year caused the cotton to 
take on a rank, heavy growth usually characterized as “mostly weed” 
or “gone to weed.” 
The first generation of worms that was noticed in this locality fin¬ 
ished their work about August 18. The cotton plants were ragged 
from the work of the worms, but the general opinion of tenants and 
owners was that more good had been done than harm. The “ragging” 
allowed more light to get in and would prevent many of the bolls from 
rotting, they said. 
On the 7th, 8th, and 9th of September the second generation com¬ 
pletely stripped the cotton in fields where the worms appeared. In 
this connection it is interesting to note that the moths, adults of the 
first generation, were attracted to the richest uninjured cotton for 
laying eggs of the second generation. In many fields already ragged 
practically no further injury occurred. The cotton on which calcium 
arsenate had been applied for control of the boll weevil, retained its 
foliage. A third generation was expected, but did not develop, al¬ 
though the eggs were laid. Control was due to the natural parasites 
which became very abundant. 
With entire fields looking brown, the first impression was that the 
damage had been great. After examination, expression was frequently 
given by the above-mentioned parties and others, that the damage was 
more apparent than real and that it didn’t hurt them. 
The opportunity was at hand to get some reliable information on 
this point under conditions existing at this time and place. 
One hundred and twenty-three stalks, newly stripped by cotton 
worms, were selected and tagged and found to possess 1,255 unopened 
bolls of all sizes. For comparison, two rows in a plot of treated cotton 
with foliage uninjured and in the same field were selected; these rows 
contained 250 stalks. All open bolls on plants and rows selected were 
