BUREAU OF ENTOMOLOGY. 219 



was conducted intensively in the Delta region of the Mississippi 

 Valley, with headquarters at Tallulah, La. 



The work of determining the causes of variation in yield of cot- 

 ton under weevil conditions under apparently similar conditions 

 was continued. Considerable attention was given to the related sub- 

 ject of local variation in weevil injury. This was studied in four 

 Delta counties of Louisiana from the standpoint of weevil emergence, 

 initial infestation, and the varying local conditions of the season. 

 The study of the relation between the spacing of cotton in the row 

 and the date of thinning indicates the best spacing to vary from 

 18 to 14 inches, according to the nature of the soil, and that the best 

 time for thinning is that usually practiced. The work on direct con- 

 trol consisted principally of plat tests of square picking, weevil pick- 

 ing, and poisoning. It has been found that with an abundance of 

 tenant labor mechanical methods of collecting squares and weevils 

 may give satisfactory results. A new type of poison-dust gun and 

 also a grade of lead arsenate containing a higher percentage of 

 arsenic have been tested, with excellent results in increased produc- 

 tion. Life history, hibernation, and parasite studies were continued. 

 Certain chemical products of the cotton plant have been isolated 

 which have proved quite attractive to the weevils. An attempt will 

 be made to utilize these substances. 



The annual spread of the boll weevil was determined, as usual, 

 and a map published in the winter showing the progress of the in- 

 sect, for the use of the State officials concerned in quarantine. 



Work on the miscellaneous insects of cotton was conducted through- 

 out the year at Tallulah, La., and Thomasville, Ga. The Batesburg 

 (S. C.) laboratory was discontinued at the end of 1915, and a new 

 laboratory was established at El Centro, Cal. The work on the 

 cotton red spider was concluded and a bulletin prepared for pub- 

 lication. Work was done at Tallulah on the mutilation of cotton 

 seedlings by insects, and at Thomasville important results were ob- 

 tained in the studies of insects which attack cotton squares and 

 blooms. In cooperation with the Georgia State board of entomology, 

 it was determined that certain species of sucking bugs transmit some 

 of the diseases of cotton. The preliminary work at El Centro has 

 resulted in the determination of the principal causes of insect injury 

 to cotton in the Imperial Valley and will be followed up by studies 

 in control. 



Tobacco insects. — Further improvements have been made in the 

 apparatus for applying arsenate of lead against the hornworms, 

 with the result that a more thorough application may be made at a 

 material reduction in cost. Farm tests were made in cooperation 

 with 280 farmers. 



Special studies in control of the cigarette beetle resulted in the 

 determination that storage of manufactured tobacco at low tempera- 

 tures furnishes an efficient and economical means of preventing loss. 

 Exposure to Roentgen rays under certain conditions is effective in 

 sterilizing the eggs of the beetles. Much of the infestation by this 

 beetle is due to improper methods of hauling and storing the tobacco 

 after it has left the factories. 



A new poisoned bait for cutworms, wireworms, and grasshoppers 

 has been tested with increasingly satisfactory results. Valuable data 



72412°— age 1916 15 



