February, '19] HEADLEE: SPRINKLING SEWAGE FILTER FLY 39 



breathe atmospheric air. Tests made and reported^ show that sub- 

 mersion of the filter bed with ordinary sewage for a period of 24 hours 

 destroys 100 per cent of the larvse and pupae, leaving the film in active 

 condition. 



The first experimental submergence was made on June 14, 1918, and 

 involved only one-fourth of the entire bed which has a surface of about 

 two acres. 



Acting upon this discovery, a bulk head pierced with a passage way 

 which may be closed or opened at will was installed in each of the two 

 galleries through which the effluent escaped from the filter bed of the 

 joint sewage disposal plant of Plainfield, North Plainfield and Dunel- 

 len; a plant which serves to purify the sewage of about 40,000 people. 



The factors affecting the submergence of the entire bed were tight- 

 ness of the retaining walls, the volume of sewage available and the time 

 which the bed could be submerged without injury. The retaining 

 walls in question were composed of six-inch concrete backed by a 

 heavy wall of soil lying at an easy angle of rest from the top of the re- 

 taining wall to the surface of the surrounding ground. This concrete 

 wall had not been constructed to hold water, but merely to hold the 

 stone in place and it surrounded a basin of approximately six feet 

 deep. The normal volume of sewage ranged from 2| to 4 million gal- 

 lons daily. The time during which the filter could be submerged and 

 not seriously injure the activity of the film as shown by the following 

 table was something less than 48 hours. 



Flooding Experiment Carried out in Flower Pots 



The figures indicated that the filter should be filled with sewage, 

 provided the walls did not leak seriously, within a period of 12 hours. 



On August 9 the bulk head gates were shut and the water allowed to 

 accumulate. The filter was completely under water at the end of 12 

 hours and was maintained in this condition for a period of 24 hours, 

 when the bulk head gates were withdrawn and the waters allowed to 

 escape. These escaping streams of water were full of the dead larvae 

 of the Sprinkling Sewage Filter Fly. 



' Headlce, T. J., Beckwith, C. S. SprinkUng Sewage Fiher Fly, Journal of 

 Economic Entomology, Vol. II, No. 5, 1918. 



