30 THE EEPOET OF THE No. 36 



occurrence of definite intermediate forms was pointed out by W. F. Turner^ 

 and the writer. These forms retain the wings in a more or less rudimentary- 

 condition and they tend to lose also the other characters which are associated 

 with the winged form. In some species like Aphis pomi DeGeer, it is possible to 

 rear an almost pure apterous line and a line with a high percentage of winged 

 forms. It is noteworthy that in certain aphid groups it is impossible to rear 

 apterous forms while in the more specialized groups the winged forms are often 

 absent for many generations. Sometimes a species may be reared for 100 or 

 more generations without a winged insect appearing. It is thus evident that 

 in the family nature has eliminated the wings to a large extent in the specialized 

 groups. 



Search has been made for the controlling' factor here and several different 

 ones have been claimed. Ewing^ worked from the standpoint of temperature 

 and in Aphis prunifoliae Fitch {avenue of authors) was able to control the 

 winged condition by varying the temperature. This species is one like pomi 

 in which both winged and wingless forms are common. Ewing also obtained inter- 

 mediates (calling them paedogenetic nymphs), adults between the winged and 

 apterous condition. Several factors were not considered in his experiments. The 

 aifect of varied temperature on the availability of food and its nature when avail- 

 able was not ascertained and the genealogy of the specimens tested was apparently 

 not considered. 



Gregory^ worked with Macrosiphum pki L., and obtained control by varying 

 the food in the previous generation. With insects from different regions, however, 

 she obtained slightly different results. Her experiments were conducted without 

 a definite temperature control and without considering the descent of her insects. 



Shinji^ has made experiments in feeding different chemicals to aphids and 

 finds that he can define two groups of compounds one of which will result in the 

 development of a high percentage of winged forms and the other of which will 

 prevent wing development. His work follows that of Clark" and is very interest- 

 ing. It is noteworthy, however, that his experiments as recorded were conducted 

 almost altogether during fall, winter or spring, and he gives no records of the 

 ancestry of the specimens whereby we can judge of the percentage of winged 

 or apterous forms which would normally be expected from the individuals treated. 

 The writer has found that in some cases the offspring of an individual will be 

 nearly all winged or apterous at the beginning of the period of reproduction 

 and the reverse toward the end of the period. It is important to remember that 

 Shinji was unal)le to produce any apterous forms in the aphid groups which have 

 not yet eliminated the wings. That is, the ancestry of these forms was more 

 important than his wing preventing substances. On the other hand, in groups 

 which are nearly all apterous he did not experiment with his wing producing 

 substances. It is curious that tannin is listed as preventing wing development 

 and yet several species develop wings while feeding on galls containing 60 per 

 cent, of tannic acid. On the other hand, sugar is given as a wing producing 

 substance and yet the writer has reared an apterous line of Eriosomn lanigem for 

 two years on galls containing an abundance of sugar. That Shinji overlooked 

 some factors is evident for he says "Macrosiphum rosae also produced alate forms 



•■' Turner & Baker — Proc. Ent. Soc, Wash., XVII, No. 1, 1915. 

 * Ewing. H E.— Biol. Bull., XXXI. No. 2, 1916. 

 •Gregory. Louise H.— Biol. Bull.. XXXIII, No. 4. 1917. 

 " Shinji, George O.— Biol. Bull., XXXV, No. 2, 1918. 

 'Clark, W. T.— Journ. Tech., U. of Cal., I, No. 3, 1903. 



