house-fly investigations. 491 



Baits for House-flies. 

 Methods and accoiont of Experime^its. 



These expeiiments on house-fly baits were carried out at 

 Acton Lodge, Brentford, during the latter half of July and in 

 August. 



The first experiments were made out of doors {a) near a 

 manure-heap, from which flies were emerging, (6) in or near 

 a forge, where a number of house-flies were congregating in the 

 warmth . 



In neither of these cases, however, were the conditions very 

 favourable, chiefly on account of the wet and windy weather. 

 Later, half a bushel of house-fly pupse was collected from a 

 neighbouring manure-heap, and placed in a greenhouse, where 

 most of the subsequent experiments were made. This green- 

 house was empty, excepting for some tomato-plants on the upper 

 shelves (the flies did not like them, and would not settle or sit on 

 the' leaves). Ventilation was secured by nailing muslin over two 

 of the windows. Very soon the greenhouse was swarming with 

 flies, which had emerged from the pupae. These flies were used 

 in the experiments. 



The supply of flies was kept up by breeding them in artificial 

 media, consisting of mixtures of bread, casein *, water, and 

 banana, and banana-skins, surrounded by a dry layer of cut 

 grass, leaves, etc., in which the maggots could pupate ; all of 

 which were placed in large saucers on the floor, under the shelves. 

 It was thus possible to keep up a continuous supply of flies. 



In experimenting, the mixtures to be used as baits were placed 

 in glass jars with wire-gauze funnels (the same as those used in 

 the blow-fly experiments). The date and time of starting the 

 experiment were noted, and usually a morning (9-11 a.m.) and 

 evening (4.30-6.30 p.m.) count of flies taken, when the jars were 

 emptied of flies and the dead (if any) removed. 



The average duration of the experiments was 8-9 days. 



The substances tested were very various. Mixtures of casein 

 and peptone, which had seemed from the blow-fly experiments 

 to be promising baits, were tried, as well as all soi'ts of other 

 substances, e. g. sugars, jams, fruits, etc., both alone and mixed 

 with casein and peptone. After some time it was found that 

 the casein mixtures were moi'e attractive than most of the other 

 substances used. Hence experiments were made to try to 

 discover when, and under what conditions, and mixed with which 

 substances these casein baits were most attractive. It was found 

 that the best results were obtained with approximately equal 

 parts of casein and brown sugar ; or casein and banana ; or 



* The idea of usinp: mixtures of casein, banana, etc. for breeding purposes was 

 suggested by the fact that eggs were laid on some of the casein and banana baits in 

 the jars, and that the larvse lived in them. It was found very successful for 

 breeding and keeping up a continuous supply of house-flies, both in this greenhouse 

 and in the " fly-room " at the Imperial College. Flies were bred in large numbers 

 from August 1915, and are still increasing (June 1916). 



