232 ANNUAL EEPOETS OF DEPARTMENT OF AGEICULTUKE. 



Chemistry and Plant Industry, studies of the poisonous spray 

 residues on fruits are being continued, and this investigation prob- 

 ably will be completed during the summer of 1917. An investiga- 

 tion of the effect on bees of spraying apple trees with arsenical s 

 when they are in bloom and after the falling of most of the petals 

 has been practically completed and will furnish the basis of a report 

 in the near future, Insecticidal constituents of plants have been 

 studied in cooperation with the Bureau of Plant Industry. Addi- 

 tional poisonous plants have been obtained, and their toxicity and 

 physiological effects on insects are being determined. In view of 

 certain surprising results obtained from the use of nicotine for the 

 control of the codling moth in the Northwest, a special study in 

 laboratory and field is being made to determine the possible action 

 of this substance on the eggs and larvge of this insect. Studies of 

 the comparative effect of pyrethrum, hellebore, and sabadella on 

 insects are well advanced, and experiments with a very promising 

 product, one of the so-called fish-poisons, presumably " Derris," are 

 being made. 



Insects attacking nursery stock. — Thorough tests of fumigants 

 and other substances in the destruction of the woolly aphis on the 

 roots of nursery stock failed to give results of much practical value 

 because of the injury to the plants. 



It has been found that by the use of 40 per cent nicotine sulphate 

 at the rate of 1 part to 1,600 parts of dilute lime-sulphur solution, 

 95 per cent of the nymphs of the first brood of the apple leafhopper 

 can be killed. Nymphs of the second brood, however, are more 

 hardy. 



SOUTHERN FIELD CROP INSECT INVESTIGATIONS. 



Dr. W. D. Hunter has been in charge of the southern field crop 

 insect investigations of the bureau as in previous years. 



Cotton insects. — The boll-weevil investigations conducted at 

 Tallulah, La., consisted of field tests of various control measures and 

 additional studies on the habits of the weevil. Extensive studies 

 on the picldng of weevils and squares have shown that owing to 

 the very slight beneficial effect obtained and the large amount of labor 

 required this can not be recommended as a control measure. Studies 

 of the " bag-and-hoop " as a means of collecting weevils and squares 

 showed that this treatment was so injurious to the plants that an 

 actual loss in cotton production was caused by its use. Very interest- 

 ing and important results were obtained from the poisoning experi- 

 ments. It was found that the use of certain arsenical insecticides 

 late in the season resulted in uniform increases in production, amount- 

 ing in some cases to several hundred per cent. Laboratory studies 

 were conducted to give additional data on the use of these insecti- 

 cides as a basis for more extensive field work in the future. The 

 cotton-spacing studies were continued to determine the relation of 

 the various spacings to the degi^ee of weevil infestation, and it was 

 found that under Mississippi Delta conditions a spacing of about 18 

 inches in the drill gives the best results. Special studies were con- 

 ducted on the relation between the characteristics of various cotton 

 varieties and weevil injury, It is hoped that sufficient data may be 



