BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 9 
With the exception of calcium arsenate, the materials were about 
equally effective when applied as concentrated sprays or in dust formu- 
lations, when the same amount of toxicant was used. Calcium arsen- 
ate was most effective as a dust. When these insecticides are used to 
control the boll weevil under field conditions, other insect problems 
must be considered. Infestations of cotton aphid, bollworm, and 
spider mites may develop when some of the preparations are used 
alone. 
Several other new insecticides have been used effectively against 
the weevil in some areas. Heptachlor, ethyl p-nitrophenyl thioben- 
zene phosphonate (EPN), and diethoxy thiophosphoric acid ester of 
7-hydroxy-4-methyl eoumarin (Potosan) have shown promise in ex- 
periments and are being extensively tested. 
In large-scale experiments in Mississippi, aldrin, benzene hexa- 
chloricle, chlordane, dieldrin, and toxaphene gave satisfactory control 
as dusts or sprays. In oil solutions some caused very little injury 
to the cotton plant. Heptachlor at a 5-percent concentration in dust, 
or 0.5 pound an acre in spray, gave satisfactory weevil control under 
field conditions. 
In field experiments in South Carolina, mixtures containing DDT 
and benzene hexachloride, lindane, chlordane, or toxaphene gave ex- 
cellent control of the boll weevil and prevented damage by the boll- 
worm when applied in either dust or spray form. Aldrin, dieldrin, 
heptachlor, and toxaphene, applied alone as dusts or sprays, also gave 
control of the boll weevil. 
Control of Thrips Increases Yield of Seed Cotton 
Aldrin, dieldrin, and toxaphene at acre dosages of 0.125 and 0.25 
pound, 0.0625 pound, and 0.75 and 1.5 pounds, respectively, applied as 
sprays to young cotton were effective in controlling several species of 
thrips in experiments conducted near Waco, Tex. Toxaphene and 
dieldrin gave longer residual control than aldrin. Less effective were 
tetraethyl pyrophosphate at a dosage of 0.25 pound and aldrin at 
0.0625 pound an acre. Increases in yield of cotton from applications 
of insecticides for control of thrips ranged from 5 to 20 percent. 
Control of thrips accelerated fruiting and hastened maturity. In one 
experiment all open cotton was picked late in August. At that time 
the cotton treated for thrip control yielded 1,558 pounds and the 
adjoining untreated cotton 762 pounds of seed cotton an acre. An- 
other picking early in October brought the total yield of the treated 
cotton to 1,750 pounds of seed cotton an acre, as compared with 1,500 
pounds in the untreated cotton, or a gain of 250 pounds an acre. 
Bollworms Checked by Control Measures Against Boll Weevil 
Damage to the cotton crop from bollworms again was comparatively 
light in 1950, although serious outbreaks were reported late in the 
season, especially in Arizona, Texas, Oklahoma, and Louisiana. The 
heavy spraying and dusting schedule for controlling the boll weevil 
in July and early August apparently held the bollworm in check in 
most areas. 
On May 2 threatening bollworm infestations were reported in the 
Rio Grande Valley of Texas, but serious infestations did not develop 
