128 Notes on Chemotrqpism in the House-Fly 



banana was pealed and cut into two halves. One half was crushed into 

 a glass dish and set under a trap. 



However, it is clearly seen that, during decomposition, banana be- 

 comes increasingly attractive, and the attractive power passes off as 

 the putrescent mass dries off. The banana used was rather overripe at 

 the start, and the results of Exp. 5 in Section II prove that the attractive 

 qualities are exceedingly small when the fruit is rather unripe, an 

 increase in the numbers being again shown when decomposition has set 

 in, in Exp. 6. 



It will have been observed that, not only with banana, but also with 

 vanilla extract as baits, there is a high percentage of mortality amongst 

 both male and female flies after they have entered the traps, and an 

 increasing mortality as decomposition proceeds in banana. 



This cannot be attributed to the fact that the flies were at the 

 extreme limits of their life-existence, for a very large proportion of the 

 female flies contained eggs, and it is clear to a degree that, in the case 

 of banana, the decomposition and fermentation products have a dele- 

 terious effect just as strong oil of citronella has upon Dacus (Howlett) 1 . 



It does not imply, however, that the decomposition products are a 

 stimulus to oviposition, for the flies were directly attracted away from 

 manure, where they were breeding, though it must be admitted that 

 some reagents in banana and manure may be similar in composition 

 as an enticement to breeding. The mortality in vanilla extract is 

 evidently attributable to alcoholic evaporation. The large proportion 

 in many cases of female to male flies is merely due to the fact that the 

 former were most abundant in the locality. 



With regard to the attractive features of glacial acetic acid and 

 spirit of vinegar, these substances might be found to have increased 

 stimulating powers when diluted to an optimum solution (see Barrows) 2 . 

 The latter reagents also produce mortality to a slight degree, grape juice, 

 when fermenting to a considerable degree, and reference is here made 

 to experiments with alcohols, aldehydes and acids described in Section II, 

 proving that this is due to the products of alcoholic, aldehydic and acidic 

 fermentation of organic substances. 



Banana, as being the most attractive substance to the house-fly, is 

 used as the basis of investigation in the next section. 



1 Trans. Ent. Soc. Lond. Part II, pp. 412-418. 



2 Journ. Exp. Zoology, Baltimore, Md. pp. 515-537. 



