104 Prochtction of Winged Forms in an Aj^hid 



Thus the results obtained by Gregory and Shinji are not wholly in 

 agreement, and neither are altogether borne out by observations made 

 in the field. Thus the maximum production of winged forms in many 

 species takes place in the third and fourth generations when food is 

 abundant, and then diminishes in a marked degree, although the apterous 

 forms may continue to feed and reproduce on the same plant for the rest 

 of the summer (1). If some of the winged females are induced to breed 

 on their birth plant, the young, exposed to the same conditions, are 

 as frequently apterous as alate. In 1918, I found that in mixed broods 

 of M. ribis, the earlier born individuals were either winged or wingless, 

 while the later born were all winged. This suggested that exhaustion of 

 the parent might influence the form of the young; but this was not con- 

 firmed by the experiment of rearing a series of generations, in which 

 the youngest born female of each brood was chosen as the parent of the 

 next (4). 



It may also be pointed out that in most species, the last individuals 

 of the whole cycle, the oviparous females, appear just before the leaves 

 fall, and are invariably apterous. It is true that the males in many species 

 are alate, but in the genus ApJiis they are usually wingless, and in other 

 genera this sex is often dimorphic, winged and wingless forms appearing 

 on the same plant. 



Thus the factors controlling the production of winged forms in the 

 Aphidini cannot be considered as determined yet, and may even prove 

 to be in part cyclical. 



REFERENCES. 



(1) BoRNER, K. (1914). Abhandl. Natnririss. Verein, Bremen, xxill, p. 145 



(2) Clarke, W. T. (1903). Journ. of Tech. U. C. Student Publ. i, No. 3. 



(3) Gregory, Louise (1917). J5io/. 5m//. xxxiii, p. 296. 



(4) Haviland, Maud D. (1919). Proc. Boy. Soc. Edvibwrgh, xxix, Pt 1, p. 78. 



(5) Neiills, J. D. (1912). Entom. News, xxiii. 



(G) .Shin.ti, Georqe O. (1918). Biol Bull, xxxv, p. 95. 



{Received May '2?,rd, 1921.) 



