BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 17 
DDT, thiocyanates, phenothioxin, and dinitro-0-cyclohexylphenol, 
have shown much promise. 
The damage per aphid was found to be greater under dry than under 
moist conditions. In rainy years cotton on fertile Delta soils will 
tolerate a population of approximately 60 aphids per square inch of leaf 
surface before defoliation, whereas under the dry conditions of 1943 
half this population caused premature leaf shed. In the drier areas 
of the West and on the soils with low water-holding capacity in the 
Southeast, cotton was defoliated by much lighter populations than in 
the Delta. 
PINK BOLLWORM 
During the last 2 years weather favorable for survival of hibernat- 
ing bollworm larvae has aided in increasing the pink bollworm popula. 
tion in the lower Kio Grande Valley. Approximately twice as many 
worms were found in cotton squares and blooms in the spring of 1944 
as in 1943. The average survival of pink bollworms in open bolls en- 
caged on August 16, 1943, was 0.75 percent; on September 18, 7.93 per- 
cent ; and on October 19, 32.05 percent. The average survival in bolls 
on standing stalks was 26.44 percent, in bolls on the soil surface 11.75 
percent, and in bolls buried 4 to 6 inches 2.54 percent. The results 
of these experiments emphasize the importance of producing cotton 
early and plowing under the crop residue as soon as possible for con- 
trol of the pink bollworm. Experiments indicate that the pink boll- 
worm does not overwinter in free cocoons in the soil in this section. 
In the Big Bend area high survivals during the winters of 1941^2 
and 1942^3 and a prolonged planting period in 1943 following the 
removal of legal restrictions also aided in an increase of pink boll- 
worms. However, the field clean-up, planting early maturing va- 
rieties, and early termination of irrigation have held the infestation 
below the levels recorded prior to 1938. As a result of late planting 
and late irrigation, some of the fields produced in 1943 large numbers 
of long-cycle larvae and the population entering hibernation was 
twice as large as in 1942. 
The use of a special meter for indicating the percentage of moisture 
without disturbing the soil permitted a more accurate study of the 
effect of moisture on the mortality and time of emergence of pink 
bollworms. Apparently two or more irrigations with a dn T ing-out 
period in between are necessary for complete pupation and emergence 
of adult bollworms. In the field a few moths emerge after the pre- 
planting irrigation, but others delay,emergence until the first or second 
irrigation of the cotton, when squares and bolls are present. * 
Dichloropropane-dichloropropylene (DD) at the approximate rate 
of 50 gallons per acre killed 81 to 100 percent of larvae in buried cotton 
bolls when injected into the soil at 18-inch intervals and at 
the same depth as the larvae, or added to irrigation water, but was 
ineffective when sprayed on the soil surface after burial of the bolls. 
The infestation in secondary host plants was correlated with their 
time of fruiting and the intensity of the pink bollworm population 
in cotton. It was definitely established for the first time that the pink 
bollworm overwinters in the seed pods of Pseudabutilon lozani (Rose) 
R. E. Fries. 
616016 — 44 3 
