DESTRUCTION OF FLY LARVAE IN HORSE MANURE. 6 



gaseous nitrogen, the extent of the loss depending on the nature of the 

 fermentation, the aerobic fermentation, due to the rapidity of combus- 

 tion, producing a greater loss than the anaerobic. To prevent this 

 loss of plant food in the course of fermentation, various chemicals 

 have been used, either to retard bacterial action or to fix the volatile 

 constituents. Among the various substances used for this purpose 

 maybe mentioned ground phosphate rock ( floats ),kainit, various lime 

 compounds, carbon bisulphid, formaldehyde, and ferrous sulphate. 



The house fly is attracted to horse manure, possibly by its odor, 

 and on alighting crawls an inch or so under the surface and there lays 

 its eggs. On account of the temperature of the manure the eggs 

 hatch within one day. The larval or maggot stage continues from 

 four to five days, during which the larvae migrate to the sides of the 

 pile and toward the base, feeding on the manure during their journey. 

 The pupae are found, after a few days, congregated in the outer edges 

 of the manure near the ground, as seen in Plate I. It is therefore 

 about 10 days from the time the eggs are laid until the mature fly 

 emerges. 



GENERAL PLAN OF EXPERIMENTAL WORK. 



Experiments were carried out at the Experimental Farm of the 

 Bureau of Plant Industry at Arlington, Va., and continued during 

 the autumn at the Experiment Station at Audubon Park, New Or- 

 leans, La._, under a cooperative arrangement entered into by the 

 Bureau of Entomology, the Bureau of Chemistry, and the Bureau of 

 Plant Industry. 



CAGE EXPERIMENTS. 



An idea of the structure of the 15 cages, which were designed by 

 Mr. W. D. Pierce, of the Bureau of Entomology, may be gained from 

 the accompanying photograph (PI. II). Each cage has an inside 

 measurement of 2 by 2 by 4 feet. The bottom of the cage consists of 

 a galvanized-iron pan 1 foot high. Above this pan bronzed wire 

 screening (16 meshes to the inch) is tacked both on the inside and 

 outside of the framework. These two layers of screening are 2 

 inches apart. In this way manure once put into the cages was protected 

 from further infestation from the outside. In order to prevent the 

 larvse from escaping from the sides of the cages through this screen- 

 ing it was found necessary to fasten sheets of tin on the inside above 

 the galvanized-iron base. These strips are 1 foot high, and thus there 

 was afforded a space of 8 cubic feet from which larvse had little 

 chance to escape. In the bottom of the cage nine small holes were 

 made which permitted excess liquids to drain off. Some larvae found 

 their way out through them, but these were caught in the pan below 

 and a record kept of the numbers thus escaping. 



