464 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 14 



In the case of sodium carbonate, standing first, it is believed that the 

 results obtained in 1917 with carbon dioxid have been confirmed. 

 Since the results with the two substances are practically identical, 

 the marked results obtained with sodium, carbonate and its chemical 

 kinship to carbon dioxid led to an investigation of the degree of acidit\- 

 developing in the moistened bran bait during the 6-hour period of 

 exposure. Additional similarly prepared check units were exposed 

 but screened from, the flies. Tested before exposure these units were 

 neutral to phenolthalein. At the end of the 6-hour period of exposure 

 they showed an acidity m.easured by the same indicator, practically 

 equal to the alkalinity obtained by the dosage used in the sodium, car- 

 bonate units. Thus it seem.s possible that a complete liberation of the 

 carbonic acid present in the sodiimi. carbonate units must have taken 

 place, and that the presence of this free carbonic acid in the moist bran 

 bait accounts for the fact t.hat 94 percent of the eggs were obtained 

 in these units. Hence the writers' conclusion that this is a confir- 

 mation of their former results with carbon dioxid. 



Sodium hydroxid is also a moderate attractant, but, m.uch as is the case 

 with the sodium, carbonate, the effect obtained is secondarv^ to a chemical 

 change which occurs in the course of the experiment. The sodium 

 hydroxid doubtless rapidly absorbs carbon dioxid from, the air, being 

 converted into the carbonate, which in turn is acted on by the organic 

 acid formed by fermentation in the moist bran medium. This sequence of 

 changes would result in accumulation of a moderate amount of free car- 

 bonic acid in the bran m.edium. as before. It will be noted that the calcium, 

 hydroxid solution proved of no effect in stimulating oviposition. As to 

 why the same result was not obtained here as in the cases of sodium 

 hydroxid and sodium, carbonate it m.ust be observed that the saturated 

 solution of calcium, hydroxid at 20 C. is approximately only a 0.176 

 percent solution and therefore less than one-sixth the equivalent chem.ical 

 strength of the sodiiun. hydroxid and carbonate solutions. Therefore 

 the amount of carbon dioxid absorbed and converted into free carbonic 

 acid in the acid bran nidus is probably negligible. In fact it is doubtful 

 whether the same chemical change would occur in full, with even the 

 same amount present, due to the relative insolubility of the calcium 

 carbonate when formed. 



In the case of sodiiun. sulphate, a moderate attraction is to be observed. 

 The results with this substance are the least satisfactory of the series 

 however, on account of the relatively small number of eggs obtained, 

 incident to weather conditions and inability to secure many gravid 

 flies. Considering together, sodium, sulphate, sodium carbonate, and 



