96 GEORGE O. SHINJI. 



exhausted. Climatic changes, especially the approach of cooler 

 weather, humidity, the wilting of host plants and many other 

 factors have been regarded as possible causes of the appearance 

 of the winged aphid. All explanations, however, have been ad- 

 vanced as the results of observations rather than as the results of 

 experimental work. 



The first experimental study of the problem was undertaken by 

 Professor W. T. Clarke, of the University of California, in 1901. 

 He planted a rose twig bearing an apterous parthenogenetic 

 female in each of a series of four-ounce tumblers. These he 

 filled with washed sand, moistened with solutions of several salts 

 or pure water. By this method, he could charge with any desired 

 solution the sap-sucking insect through the plant. He was in- 

 fluenced, so he states, in his choice of chemicals by the chemical 

 analysis of the ingredients of plants. Professor Clarke used 

 sodium hydroxide, sodium phosphate, magnesium sulphate, 

 magnesium chloride, and distilled water as a check. As a result 

 of such experiments, he found that among these substances only 

 the magnesium salts would produce winged aphids. Changes of 

 temperature, he suggested, may not be a factor in the develop- 

 ment of the wing in aphids. 



In 1908 Professor C. W. Woodworth expressed his views on the 

 problem. He stated that he believed that the wilting of plants 

 might help develop the wing by retarding the growth of other 

 parts and giving an even chance for the wing buds to develop. 



Mr. J. D. Neiils, who studied the problem in 1912, not only con- 

 firmed the findings of Clarke, but also pointed out a new fact that 

 three days were usually required for the magnesium salts to pro- 

 duce a large number of winged aphids. Further, he found that 

 the young aphids become winged, if they are subjected to the 

 magnesium solutions within three days after birth. 



Professor Clarke, and also Mr. Neiils, worked on a single 

 species, namely, the common rose aphid, using the limited series 

 of chemicals above mentioned. In order to determine whether 

 other salts than those of magnesium would have a similar effect 

 on the production of winged aphids, and also to determine 

 whether the results of Clarke and Neiils were applicable to other 

 species of aphids, I undertook an experimental study of the 

 problem. 



