PHYSIOLOGY OF WING DEVELOPMENT IN APHIDS. 115 



cals. For the sake of making a distinction between these two 

 groups of substances, we may call the former the "wing-develop- 

 ing" substances, and the latter, the "non-wing-developing" 

 substances. 



3. As far as the tests go, the salts of the alkalis (Na, Cl, K, 

 etc.) and alkaline earths (Ca, Br) with the exception of magne- 

 sium, distilled water, urea, alum and others were shown to belong 

 to the non-wing-developing substances, while the salts of the 

 heavy metals, and of magnesium, sugar, and perhaps some others 

 belong to the category of wing-developing substances. 



4. The wing-developing substances were only effective when 

 applied within a certain period after birth. This period varied 

 with temperature and also with the species, e. g., the maximum 

 time for the rose aphis, Macrosiphum rosce L., during the early 

 summer was found to be from 2 to 3 days, while under the same 

 conditions from 5 to 7 days was the maximum in the case of the 

 sonchus aphids, Macrosiphum solanifolicz Ashm., the mustard 

 aphis, Aphis brassicce L., etc. 



5. The amount of magnesium salts and also of other wing- 

 developing substances needed to produce winged aphids was very 

 small. Subjection to a m/ioo solution of magnesium sulphate 

 for 12-24 hours produced nearly one hundred per cent, of winged 

 aphids, so far as Macrosiphum rosce was concerned. 



6. When twigs planted in the sand saturated with distilled 

 water and calcium chloride were subjected to a drying process, 

 the young aphids born on these twigs remained apterous, whereas 

 on those that had been charged with solutions of magnesium 

 salts or some other wing-developing substances, the greatest num- 

 ber of the winged aphids appeared. 



7. When newly born aphids are subjected to a mixed solution 

 of wing-developing and non-wing-developing substances, winged 

 aphids may or may not appear, according to whether or not the 

 solution contains an excess of the wing-developing over the non- 

 wing-developing substances. 



8. Variation in temperature, or a sudden change from as high 

 as 100 F. to as low as 35 F., failed to produce winged aphids on 

 the twigs charged with non-wing-developing substances. 



