72 ANNUAL REPORTS OF DEPARTMENT 01 AGBICULTUBE, 1939 
mately equal, the increases being 204 and 210 pounds, or 23 percent. 
The cryolite containing 90 percent of sodium fluoaluminate increased 
the yield L2.5 percent, and a cryolite with coarse particles containing 
78 percent of sodium fluoaluminate, only 9.5 percent. In comparisons 
of calcium arsenates containing high (10.5 percent), medium (4.5 
percent), and low (0.4 percent) water-soluble arsenic as determined 
by the New York met hod the Increases in yield- over the checks were 
402, 309, and 531 pounds of seed cotton, respectively. 
In tests at College Station extending over 10 year- calcium arsenate 
dust applied at the rale of * to 10 pounds per acre, beginning when 
from 25 to 35 eggs per LOO terminal buds are present and repeated at 
5-day intervals as long as oviposition continues, has proved the most 
effective and economical for control of the bollworm. The effective- 
ness of the insect icide depend- on the distribution and timeline-- of the 
applicat ion. 
PINK BOLLWORM 
The infestation of the pink bollworm in the Big Bend area of Texas 
in 1938 was much heavier than in previous year-. A very early tall 
clean-up of the crop debris, together with overflows from the Rio 
Grande in July and September, which left the soil unusually moist, 
materially reduced the number of worms entering hibernation and the 
winter survival and resulted in a low carry-over to the Spring of 
Experiments to determine the percentage of worms going into hiber- 
nation at different dates showed that 0.33 percent of the larvae issuing 
from green bolls between September 1 and 15. 7 percent of those issuing 
between September 16 and 30. and 20 percent of those issuing between 
October 1 and 15 were of the long cycle. The experiments were inter- 
rupted by the floods but clearly indicate the value of the early fall 
destruction of cotton stalks, since it is known that practically all the 
larvae maturing later in the season go into hibernation. Larvae in 
bolls plowed under inches deep early in December, in field- afterwards 
given two winter irrigations, again had the lowest survival. The time 
and rate of moth emergence in the spring were 1 influenced by the tem- 
perature and the amount of moisture in the soil. When the larvae were 
kept over winter under optimum moisture conditions or the moisture 
wa- increased in the spring by an irrigation, they pupated earlier and 
moth emergence was completed sooner than when soil moisture was 
low. There was a higher survival in heavy adobe -oil- than in light 
sandy soil-, and in cocoons left on the -oil surface than in those buried 
^ to 6 inches deep. Bolls of Thurberia thespesioides were readily at- 
tacked by the pink bollworm when grown in close proximity to infested 
cotton, and moth- emerged from larvae overwintering in boll- kept in 
hibernal ion cages. 
In the work with parasites, the stocks of the Hawaiian strain of 
Microbracon mellitor (Say) were liberated and breeding of this species 
was discontinued for the present. A total of 93,000 .V. niprarufum 
Cush. and 497,000 Chi Ion us blackbwrni Cam. were liberated during the 
year in the IVe-idio Yallev of Texa- and the Laguna and La- Delicias 
districts of Mexico. The liberations were made in Texas early in the 
season, bul the shortening of the breeding period by flood- and early 
clean up made conditions very unfavorable. Both species were re- 
covered near the point- of liberation, bm definite establishment lias 
not been determined. 
