DESTRUCTION OF FLY LARViE IN HORSE MANURE. 13 



effect of 99 per cent. Pyridine was used in two open-pile experiments 

 in a dilution of 1 to 1,500 (Table IV, Series 48, A and B), and 8 and 

 47 per cent of the larvae were killed. 



It is impossible satisfactorily to explain the differences in the larvi- 

 cidal efficiency of the pyridine in the cage and open-pile experiments 

 where the 1 to 500 dilutions were employed. Different samples of 

 pyridine were used in these two tests, and as the conditions are very 

 different at Arlington and New Orleans the exact larvicidal value of 

 the 1 to 500 dilutions is uncertain. As the 1 to 1,500 is the only dilu- 

 tion that is practical from a cost point of view and the larvicidal 

 effect of this strength was low, this substance is hardly thought to be 

 worthy of further consideration as a larvicide. The extremely disa- 

 greeable odor as well as the toxicity of pyridine makes its use in 

 this work objectionable. 



PLANT MATERIAL TESTED. 



In looking for substances of an organic nature it seemed advisable 

 to test material from several common plants and weeds, especial 

 attention being given to those that are very abundant and therefore 

 cheap. 



Dr. Alsberg suggested the use of plants containing saponin, corn 

 cockle being named as a waste product containing considerable 

 amounts of this compound. Agave, a saponin-containing plant 

 growing abundantly in Texas and Florida, was obtained by Mr. W. D. 

 Hunter and was tried in two experiments. Other plant material, 

 some of which contains alkaloids, were also included in the investi- 

 gation, namely, "blackleaf 40" (an extract of tobacco), larkspur, 

 hellebore, ox-eye daisy, pyrethrum, and stramonium. 



Corn cockle. — Corn cockle (Agrostemma giihago) is present in wheat 

 screenings. The screenings used in this work contained about 43 per 

 cent of corn cockle, and hemolytic tests l showed the presence of 

 considerable saponin. The screenings were ground and then extracted 

 with water for 12 hours. Nine cage experiments at Arlington, using 

 extracts of the screenings containing from 0.3 of a pound to 5 pounds 

 per 10 gallons, were tried, and the highest apparent larvicidal action 

 was 49 per cent. These results varied markedly, and in certain cases 

 no larvicidal effect was obtained. Many bacteriological and chemical 

 analyses showed no change in the number of organisms or the compo- 

 sition of the manure. 



Agave. — The roots of several agave or soapweed plants {Agave 

 lecheguilla) were macerated and water extracts prepared. Two and 

 one-half pounds of the finely divided roots were extracted for 12 



1 The hemolytic tests were made by Dr. C. S. Smith, of the Bureau of Chemistry. 



