66 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE, 19 I 
crops in the South. Either pyrethrum or derris was effective against 
the newly hatched larvae <>}" the southern armyworm, but the de 
of efficiency decreased rapidly after the larvae had reached the quarter- 
grown stage. 
In addition to being effective in combating the tomato rruitworm, 
tomato pinworm, southern armyworm, celery Leaf tier, and imported 
cabbage worm, cryolite has given indications of being useful in com- 
bating bornworms on tobacco. For this purpose a dust mixture con- 
taining >'• percent of cryolite is used, or a spray is made with 6 pounds 
of cryolite containing 85 percent of active ingredients and 50 gallons 
of water. Ii appeal- that cryolite Is not so likely to burn or discolor 
the plant or leave an objectionable residue on the harvested product as 
pari- green or other arsenicals commonly employed. 
Alt hough during the season of L937 cryolite was used successfully as 
a dip for tobacco plant- prior to setting, to protect them from injury 
by the corn root webworm, a serious pest of tobacco in many districts, 
the work ill 1938 did not verify the results of the previous year. Some 
indication- were obtained that cryolite may he of value in the control 
of the tobacco flea beetle, the strawberry weevil, and the beet army- 
worm. When used as a spray or as a dust mixture cryolite has not 
proved so effective against the Mexican bean beetle a- derris or cube, 
but it was more effective than either derris or cube in controlling the 
corn earwoi m on lima bean-. 
Because of its chemical composition, cryolite i- difficult to apply as 
[i dust mixture, and it seem- essentia] that some carrier be used with it 
to improve its dusting qualities. The indication- are that if a satis- 
factory degree of insect mortality is to be obtained with cryolite it 
must not be diluted more than 50 percent. Although in general the 
synthetic and natural form- of cryolite have been almost equally toxic 
when tested on properly replicated plot-, there have been occasions 
when a commonly used domestic brand of synthetic cryolite seemed 
superior to a widely distributed imported brand of the synthetic 
material. 
While insecticides containing rotenone derived from derris, cube, or 
devil'.- shoestring {TepJurosia) have proved effective against such in- 
sects a- the Mexican bean beetle, imported cabbage worm, cabbage 
[coper, diamondback moth, pea aphid, turnip aphid, pea wee^ il. rasp- 
berry fruit worm, tobacco ilea beetle, common red spider, and certain 
specie- of thrips (Thrips tabaci La nd., Heliothrips haemorrhaidoMs 
(Bouche), and Taeniothrips xcmthii William-) on greenhouse-grown 
cucumbers and tomatoes, they have not proved effective against the 
celery leaf tier, southern armyworm, tomato fruit worm, tomato pin- 
worm, tomato and tobacco worm-, zebra caterpillar, mole crickets 
(Scapterwcw spp.), sweetpotato weevil, cutworms, and leafhoppers. 
In general, derris and cube, when containing approximately the same 
total active ingredients, have given approximately the same degrt 
efficiency against any given insect. 
In special te>ts it was shown that spray- containing lead arsenate 
were superior to sprays containing derris. phenothiazine, or sulfur ni- 
tride for the control of the Colorado potato beet le. 
Some of t he commercially prepared organic thiocyanates have given 
promising results against the more common species of mealybugs and 
the common irA spider, although causing a variable degree of injury 
i me Bpecies of suscept ible plants. 
