24 



in ground-pools and artificial receptacles ; A. (C.) pidipennis, Phil., 

 from Chile and Argentina, the larva miknown ; A. (C.) braziliensis, 

 Chagas, from Brazil, the larva miknown ; A. (C.) tarsimaculatus, 

 Goeldi, from the tropical American mainland and Lesser Antilles, 

 the larvae in any kind of ground-pools except artificial ones ; and 

 A. (C.) albimanus, Wied., from tropical America, including the greater 

 Antilles and southern Florida, the larvae in ground-pools, often of 

 brackish water. 



Headlee (T. J.) & Beckwith (C. S.). Sprinkling Sewage Filter Fly, 

 Psychoda alternata, Say. — Jl. Econ. Entom. Concord, N.H., xi, 

 no. 5, October 1918, pp. 395-401. 



Psychoda alternata, a small, light- coloured, moth-like fly has proved 

 to be a serious nuisance wherever sprinkhng filters have been utilised 

 for the purification of sewage, penetrating into houses situated f mile 

 or less from the sewage plant, and being popularly accredited with 

 carrying various infectious diseases. 



The eggs are laid upon the surface of the stones in the filter bed in 

 irregular masses of from 30 to 100, and hatch in from 32 to 48 hours 

 at a temperature of 70°F. The larvae on hatching make their way 

 into the film, where they thrust their breathing tubes through the 

 film itself and exist in much the same manner as mosquito larvae. 

 They are present throughout the filter from top to bottom, but most 

 abundant in the zone from 3 to 12 inches below the surface. The 

 larval stage lasts from 9 to 15 days, and the pupal from 20 to 48 hours 

 at a temperature of 70° F. With the beginning of warm weather the 

 flies emerge from the over-wdntering larvae and pupae in such immense 

 numbers as to inconvenience those working at the filter beds, but with 

 the breaking-down and sloughing-ofE of the over-wintering film, the 

 flies rapidly disappear. As the summer film becomes heavier the flies 

 increase in abundance, until in August they reach a density greater 

 than that of spring, their abundance being thus correlated with the 

 thickness of the film, within which, and on which, the larvae feed. 



Experimental attempts to control this pest in the larval and pupal 

 stages by means of insecticides such as borax, hypochlorite of lime, 

 stone lime, copper sulphate, iron sulphate, pyrethrum, carbon bisul- 

 phide, Black-leaf 40 and a saturated solution of hellebore, showed that, 

 in general, the minimum dosage for the fly was destructive to the film. 

 The most promising of the above substances, hypochlorite of lime, 

 destroyed only 85 per cent, of the larvae and considerably injured 

 the film. 



The placing of a stone from the filter bed in water over-night to 

 await examination in the laboratory next day, accidentally led to 

 the discovery that 100 per cent, of the larvae and pupae are killed 

 by drowning in 24 hours. This was confirmed experimentally by 

 submerging the sprinkhng sewage filter for 24 hours with the ordinary 

 sewage, the results showing that by this simple means P. alternatu 

 and the less important allied species, P. cinerea, may be completely 

 destroyed without in anyway impairing the film upon which the 

 efficiency of the sprinkhng sewage filter depends. 



