14 BULLETIN 245;, U. S. DEPARTMENT OF AGRICULTURE. 



hours in 10 gallons of water. This extract was used in two cage 

 experiments and showed a larvicidal action of 82 and 84 per cent. 

 The manure was unaffected chemically, and the bacterial count on 

 one of these samples was considerably higher than the control counts. 



" Blackleaj Jfi." — "Blackleaf 40/' an extract of tobacco (Nicotiana 

 tabacum), containing 40 per cent of nicotine sulphate, is used to a 

 considerable extent as an insecticide, and it seemed worth while to 

 test its effect on fly larvae. It was tried in three cage experiments at 

 Arlington, Va., diluted 1 to 50, 1 to 250, and 1 to 500. In none of 

 these cases did it show any larvicidal action. 



Larkspur. — Ground seeds of larkspur (Delphinium) were tested, 

 using solutions prepared by treating 1 pound of the ground seeds with 

 10 gallons of 1 per cent sulphuric acid and allowing them to extract 

 for 12 hours. The extract was applied undiluted, diluted 1 to 5, and 

 diluted 1 to 15. The apparent larvicidal effect varied from 57 to 90 

 per cent. The bacteria were not affected by the application of the 

 undiluted extract, and the only change in the manure noted was a 

 decrease of alkalinity due to the acid present in the extract added. 



Stramonium. — A sulphuric-acid extract of the ground leaves of 

 stramonium (Datura stramonium) was prepared by mixing 1 pound 

 of the ground dried leaves with 10 gallons of 1 per cent sulphuric 

 acid and allowing this to stand for 12 hours. This extract was 

 employed undiluted, diluted 1 to 5 and 1 to 15. The larvicidal 

 results were not as satisfactory as those obtained above where lark- 

 spur extracts were employed. The bacterial count on manure 

 treated with the undiluted extract was lowered somewhat, and the 

 reaction showed a slight reduction in alkalinity due to the sulphuric 

 acid present in the extract applied. 



Hellebore. — Roots of hellebore {Veratrum album and Veratrum 

 viride) were used both in a ground and in a powdered condition. As 

 the following results will show, the powdered hellebore proved to be 

 the more effective. Both 1 per cent sulphuric acid and water extracts 

 of ground hellebore were used in cage experiments at Arlington 

 (Table VI, Series 82, 92, 102, and 103), and the results indicate a high 

 larvicidal action. 



