226 HENRY H. P. SEVERIN AND HARRY C. SEVERIN 



fruit fly to kerosene is not in any way connected with the feed- 

 ing habits, but too much emphasis, however, should not be 

 attributed to any of these experiments, for the distance that 

 kerosene will attract the flies is not known. 



Weinland (2, page 847) claims that the sphere of influence of 

 kerosene ' is limited, being possibly fifty feet or so, varying 

 with the wind, freshness of kerosene, etc." Howlett (1, page 

 414) of India says the distance at which the fruit flies (Dacus 

 zonatus Saund.) are able to perceive the smell of citronella 

 oil "is doubtful, but seems to be considerable; half a mile is 

 probably not extravagant an estimate if the wind is favorable." 



The behavior of the Mediterranean fruit flies was occasion- 

 ally observed in the neighborhood of the kerosene traps. In 

 some instances fruit flies remained at rest on the inside of the 

 pans for long periods of time as if stupefied by the volatile parts 

 of the oil. In other cases, the flies would walk along the inside 

 of the pan for a time, then take wing and fly up to a neigh- 

 boring leaf or twig, or in their apparently dizzy, zigzag flight 

 over the surface of the oil they would plunge into the kerosene 

 and generally cease all activity noticeable to the naked eye in 

 less than half a minute. 



It certainly is peculiar that the Mediterranean fruit fly plunges 

 into the kerosene to its own destruction. The flies may be at- 

 tracted to the oil as a result of a chemotaxis due to one or more 

 hydro-carbons or to the impurities of the petroleum oils, such 

 as the sulphur constituents or nitrogenous products. Small 

 quantities of sulphides are detected by the human nose and it 

 may be possible that the minutest traces are perceived by the 

 fruit flies. Furthermore, sulphides have recently been found 

 within the bodies of insects. Again, the hydro-carbons of the 

 oil may act as an anesthetic, and stupefy the insects whenever 

 they remain within its influence. It is known that the volatile 

 parts of gasoline, for instance, have a stupefying effect upon 

 animals. According to a scientist connected with the Standard 

 Oil Company, cases are on record where men, who had opened 

 barrels of gasoline, were suddenly overcome by the fumes and 

 plunged "head-first" into the oil. Large gasoline tanks which 

 have been recently emptied are dangerous for men to go into, 

 and require about twenty-four hours of ventilation before they 

 are safe for a human being to enter. 



