t February, '17] RICHARDSON: HOUSE-FLY FOODS 103 



during the summer of 1916 and form a part of a larger project on the 

 responses of the house-fly to environmental factors undertaken by the 

 Entomological Department of the New Jersey Agricultural Experi- 

 ment Stations. (Richardson 1916.) 



A study of the food preferences of this insect is beset with numerous 

 difficulties. Temperature and light affect the abundance, but more 

 puzzling is the great difference in numbers often noted on two consecu- 

 tive days when conditions of temperature, moisture and light appear to 

 be nearly uniform. Many explanations are offered such as the ap- 

 pearance of new broods, disposition to migrate and the desire to vary 

 the diet. These conditions necessitate the repetition of all experi- 

 ments as isolated tests may lead to erroneous conclusions. The data 

 given here must be considered as a preliminary treatment of this 

 subject, awaiting further verification and extension. 



Historical 



Morrill (1914) studied the response of the house-fly to a variety of 

 foods, some of the results of which have a direct bearing on the present 

 investigation. Sucrose was comparatively unattractive when used in 

 aqueous solution with formaldehyde. The addition of ethyl alcohol 

 (95 per cent), one part to twenty parts of water, increased its attract- 

 iveness. Vinegar in combination with sucrose was eagerly sought 

 by house-flies. This may be due to the acetic acid contained in it. 

 Ethyl alcohol when added to beer did not form an attractive mixture. 

 This result can probably be explained by the fact that American beers 

 have an alcohol content close to the optimum for the house-fly. The 

 addition of alcohol would render it less attractive. Morrill's studies 

 point out the irregularity of response to the same bait on different 

 days. 



Buck (1915) conducted a similar series of experiments. He found 

 that not less than 3 per cent nor more than 8 per cent of 95 per cent 

 ethyl alcohol in water was a good bait. Sucrose was also found to 

 be a valuable addition to various baits, sometimes increasing their 

 attractiveness from 10 to 20 per cent. 



Methods 



The experiments which are described here were performed on a shelf 

 along the south side of a barn in a well-lighted location where flies 

 were always plentiful. Screen-wire fly traps, 9f inches high and 6 

 inches in diameter were used in all experiments. The screen was given 

 a coat of spar varnish to prevent rusting. White glazed earthenware 

 dishes, 122 mm. in diameter with a capacity of 125 cc. were used as 

 containers for the solutions. The metal trap pans and dishes were 



