BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 65 
ant than usual early in the spring. In spite of the low survival in hibernation 
cages and in Spanish-moss, in Louisiana and South Carolina holl weevils were 
found under the leaves and trash in the woods close to cotton fields. In the 
vicinity of Tallnlah, an average of 141 live weevils per acre were found under 
Leaves and trash within 100 yards of cotton fields, while at Florence, where the 
collections were made within 50 yards of the edge of the woods, an average of 
311 live weevils per acre were found. These studies indicate the importance in 
any boll weevil control program of giving special attention to the destruction 
of overwintering weevils on the surface of the soil in protected places near 
cotton fields. 
A study of the characters of cotton that may be resistant to the boll weevil 
was made with many varieties during the season of 1935, in cooperation with 
the State experiment stations at Stoneville, Raymond, Natchez, Foplarville, and 
State College, Miss., and at St. Joseph and Baton Rouge, La. It was found that 
more cotton damaged and destroyed by weevils occurred among those varieties 
that had thin carpel coverings than among those that had thick coverings, al- 
though the damage among the latter extended to a greater age. Practically no 
boll weevil eggs were deposited in any variety at any location until squares 
became scarce. When 30 varieties were planted 2 months later than the normal 
planting time, the cottons bearing bolls with thick-walled carpels produced 
fewer bolls than those bearing bolls of the other type. In these experiments 
the percentage of cotton loss was greater on plants having bolls with thin 
carpel walls and tough linings than on those with bolls having thick carpel 
walls and less tough linings. According to commercial standards of grading 
and a technical color classification, the damaged cotton from bolls with thick 
walls had more brilliance damage and more discoloration than that from bolls 
with thin Mails. When a very hairy and a very smooth variety of cotton were 
studied at Stoneville, Miss., in relation to the adherence of dusted calcium 
arsenate, it was found that the hairy variety retained more arsenic pentoxide 
under all like conditions, but this was especially the case when plants were 
dusted dry. 
About 80 percent of all the boll weevil parasites reared in the different States 
have been Microbracon meUitor Say. Other species of importance are Triaspis 
curculionis Fitch, Eurytoma tijlodermatis Ashm., Catolaccus hiniteri Cwt'd., 
Zatropis incertus Ashm., Eupelmus cyaniceps amicus Gir., and Miiiophasia 
glohosa Tns. Apparently about 6 percent of the boll weevil larvae are para- 
sitized. Occasionally parasitization has run as high as 30 percent, and in a 
few areas it lias remained as high as 20 percent throughout the season. Among 
the parasites introduced in the hope of obtaining one that might effectively 
control the pink bollworm there is one, Microhracon kirhpatricki Wilk., from 
Kenya Colony, Africa, that may prove of value against the boll weevil. It 
seems to be even more effective than the native parasite M. meUitor, as it lays 
more eggs and has a shorter life cycle. 
SOIL INJURY FROM CALCIUM ARSENATE 
The investigation of possible injury to soils by the extensive use of calcium 
arsenate for boll weevil control has been continued. At Tallulah, La., a held 
plot receiving calcium arsenate at the rate of 400 pounds per acre annually 
beginning in 1931 has now received a total of 2,000 pounds of calcium arsenate 
per acre and produced seed cotton during the 5-year period at the average rate 
of 1,778 pounds per acre as compared to 1,795 pounds in the untreated plot. On 
the other hand, there may be danger of injuring the soil for other crops by the 
use of excessive quantities of calcium arsenate, since soybeans and cowpeas 
planted on the treated soil soon died although they grew normally on the 
untreated soil. 
In Mississippi an intensive study has been begun of the effect of calcium 
arsenate on seven of the major soil types and on the crops grown on them. 
Plots of each type of soil received calcium arsenate at the rate of 50, loo. 200, 
400, 800, and 1,600 pounds per acre. The germination of cotton was 1 1 < • t affected 
in any of the plots where less than 1,000 pounds of calcium arsenate per acre 
was used, but many of the seedling plants died on plots where calcium arsenate 
had been applied at the rate of 800 and l.GOO pounds per acre. The germination 
of corn was not affected in any of the plots, hut many seedling plants died 
where applications of 400, 800, and 1,G00 pounds of calcium arsenate per ;:no 
101897—36 5 
LIBRARY 
STATE PLANT BOARD 
