BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 65 
containing tartar emetic alone at the rale of 4 pounds to 100 gallons 
of water gave no appreciable control of the thrips, demonstrating the 
necessity of using some type of sweet substance in the spray to obtain 
satisfactory results. In this connection no attempt has been made 
thus far to determine the comparative effectiveness of brown sugar 
and other easily available sweet substances that might be used in com- 
bination with tartar emetic as a spray for gladiolus thrips control. 
(6) A spray containing nicotine sulfate (1 to 500) with karaya gum 
(1 to 500) was also ineffective, as was tartar emetic, at a dilution of 4 
pounds to 100 gallons of water with a commercially prepared sodium 
oleyl sulfate as a wetting agent. 
In tests to determine the quantity of mercuric chloride (corrosive 
sublimate) that is absorbed by the gladiolus conns when they are 
soaked in a solution of this chemical in the spring to combat any 
thrips that may be resident thereon, it was found that from 37 to 69 
percent of the chemical was removed from a 1 to 1,000 solution, in 
the presence of temperatures of 60° and 70° F., respectively, when 
the gladiolus corms, encased in burlap bags, were immersed in the 
liquid for a period of 17 hours. No significant differences could be 
detected between the results obtained at the two solution tempera- 
tures. Attempts to use the solutions for a second bath of corms, by 
recharging with approximately one-half the original quantity of the 
chemical, by weight, resulted in the production of solutions of vary- 
ing strength which could not be relied upon to kill gladiolus thrips on 
the corms. It was concluded, therefore, that to obtain a satisfactory 
reaction from the mercuric chloride treatment a fresh solution should 
be prepared for each batch of corms to be treated. 
RELATIVE VALUE OF VARIOUS INSECTICIDES IN COMBATING PESTS OF 
VEGETABLES, BERRIES, TOBACCO, AND ORNAMENTALS 
During the progress of experiments to determine the identity and 
proper dilution of insecticide materials that w T ould control certain of 
the pests attacking vegetables, berries, tobacco, and ornamentals and 
not leave harmful residues on the market product or injure the plant 
seriousl}-, it has become apparent that some of these materials are 
characterized by specific responses, as disclosed by tests in the labora- 
tory and in the field. 
For example, it was found that pyrethrum is very effective against 
the celery leaf tier, whereas derris is noneffective, and lead arsenate 
and cryolite are not sufficiently effective against the half-grown or 
nearly full-grown stages, at the dilutions ordinarily considered prac- 
ticable, to warrant the risk of residue hazard incurred by their use. 
On the other hand, comparable tests with these four insecticides showed 
that derris and pyrethrum were highly specific against all stages of 
the imported cabbage worm and much more effective than either lead 
arsenate or cryolite. These results emphasized that the organic insec- 
ticides enumerated could be used in controlling this important pest of 
cole crops without danger of harmful residue and that ihe other 
materials were not so suitable. 
In experiments for controlling the southern army worm it was found 
that to the insect at quarter-grown or larger stages either pyrethrum or 
derris was very nearly nontoxic, but that either cryolite or lead arsenate 
was specific against lliis widely distributed pest of many vegetable 
188590—10 5 
