318 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



tlio aiiiouiit of arsenic rendered soluble inside of the insects, and this 

 solubility depends directly upon the stability of the coniixjund. 

 These comparative studies of arsenicals as insecticides are now near- 

 in(r completion, and a rei)ort will be prei)are(l at the close of the pres- 

 ent season. Much experimental work has been accomplished with 

 contact insecticides in an effort to find something to replace nicotine 

 or tobacco extract. These studies have included testing of various 

 fractions of mineral oils and a very large list of miscellaneous chemi- 

 cals. In cooperation with the Biireau of Chemistry special atten- 

 tion has been given to organic contact insecticides and a compound 

 lias been discovered of the pyridine series which offers hope of suc- 

 cess. Much work has also been accomplished in a study of the vita- 

 mines in insect nutrition as bearing on the food re(iuircments and 

 choice of food of insects. In addition to the foregoing investigational 

 work the usiuil amount of testing proprietary and other insecticides 

 in orchards has been conducted to keep the office informed on the 

 merits of these as they appear from year to year. 



VEGETABLE AND TRUCK CROP INSECT INVESTIGATIONS. 



Investigations of the insects affecting vegetable and truck crops 

 have been carried on under the direction of Dr. F. H. Chittenden. 

 as heretofore. 



Sweet-potato weevil ePvAdication and control. — Intensive work 

 on this project has been continued, although handicapped by a short- 

 age of funds. Since the infested area, comprising portions of six 

 States, was well determined during the preceding year, efforts were 

 restricted to actual eradication and to investigational work. In 

 Florida very favorable results have been secured by cooperative 

 clean-up measures with the farmers. This Avork has been closely 

 followed by the inspectors, and where proper cooperation had not 

 been shown by the farmers themselves, all old banks were burned 

 and volunteer plants pulled from old fields. A close reinspection 

 has been continued over the infested area. It is gratifying that no 

 infestations outside of the original area have been found, 401 farms 

 being under continual supervision. In cooperation with the State 

 Plant Board of Florida, about a million weevil-free draws were 

 distributed to 214 farms previously infested. It appears that the 

 infested area in Florida and Georgia has been materially reduced 

 and that marketable crops are being produced where three years ago 

 sweet potatoes were annualh^ rendered useless through weevil attack. 



In Alabama 30 farms in a well-circumscribed locality were found 

 to be infested, and careful clean-up measures were carried out, with 

 the result that our inspectors have been unable to find a single weevil 

 during- the harvesting and planting season this year. It is accord- 

 ingly believed that Alabama may now be declared weeA'il free. This 

 will, however, be determined by a thorough inspection of the coming 

 harvest. 



In Mississippi activity has been similar to that in the more eastern 

 States. Two himdred and thirty-two infested farms now remain. 

 All of these were planted with weevil-free draws during the past 

 spring, and it is at present impossible to judge definitely as to the 

 actual reduction in infestation. Nearly one and one-half million 



