BUREAU OF ENTOMOLOGY AND PLANT QL A RAN TIN E 
M 
Seven applications of 15 pounds per acre were made in most of the 
fields at an average cost of $1.17 per acre per application. From the 
experience gained it is believed, however, that four applications would 
have been sufficient in most cases. Weekly records of the insect popu- 
lations and form counts showed that the insects in some fields did not 
reach what are considered to be commercially damaging populations, 
and in no fields were the populations very heavy. However, the 
experiment was carried through as planned, since one of the aims was 
to determine what insect population would show a profit from control 
operations. Increases in yields ranging from 2.5 to 40.4 percent were 
obtained. In the five fields of short-staple cotton the gain was 123 
pounds of seed cotton per acre, or 6.9 percent ; in the fields of long- 
staple cotton the gain was 152 pounds, or 20 percent. The populat ion 
and yield records indicate that while some increase in yields could be 
secured from dusting when infestations were light, control by air- 
plane would not be justified unless at least 12 to 15 bugs of the inju- 
rious species could be collected with 100 strokes of a sweep net. 
BOLLWORM 
Most of the bollworm damage in the experimental plots at Waco, 
Tex., was caused late in the season by the second generation of worms 
on cotton. Special attention was given to the use of cryolites for 
control. Cryolites containing 97. 90, 83. and 30 percent of sodium 
fluoaluminate and lead arsenate dusts gave nearly equal control, with 
increases in yields ranging from 316 to 387 pounds of seed cotton per 
acre, or 110 to 126 percent, over the checks. A cryolite-sulfur dust 
containing I6V2 percent of sodium fluoaluminate increased the yield 
only 29 percent. Barium fluosilicate and calcium arsenate gave in- 
creases of 64 and 56 percent, respectively. In laboratory tests where 
cotton leaves, cotton squares, or sliced cotton bolls were dusted with 
the same insecticides that were used in the field tests, from 20 to 100 
percent mortalities of second- and third-instar bollworms occurred 
within 120 hours. In some tests with cryolite and calcium arsenate 
100 percent mortality was secured with no noticeable signs of feeding 
on the dusted material as compared with only 5 percent mortality 
in the checks. The highest mortality in these tests always occurred 
where heavy applications were used, although more feeding was noted 
with the light and intermediate applications. 
PINK BOLLWORM 
A light carry-over of pink bollworms from the 1938 crop and an 
early maturity of the 1939 cotton resulted in lighter infestation and 
damage in the Big Bend area of Texas than at any time in recent 
years. Sufficiently heavy infestations for insecticidal control did 
not develop until very late in the season, and the large-scale dust- 
ing experiment was postponed. Pink bollworms in infested bolls 
under hibernation cages survived the winter of 1939-40 at Malaga, 
N. Mex. This is the first positive record of winter survival of the 
pink bollworm in Xew Mexico or in the slightly infested adjacent 
areas in Texas, or in Arizona. 
In experiments in cultural control the planting of quick-maturing 
eastern varieties of cotton developed for boll weevil conditions, 
267756 — 40 6 
