THE OAT APHIS. 13 
it alternately froze and thawed until March, 1910, the weather 
being so severe that 50 to 75 per cent of the wheat in that vicinity 
was killed by the cold. 
Sometimes these winter root forms are attended by ants, as has 
been observed by Prof. Webster and the writer. The forms which 
go to apple migrate early in October in the latitude of La Fayette, 
Ind., and usually fully a month later in the latitude of northern 
Oklahoma. In the rearing cages it has never been possible to get 
the forms from wheat to migrate to apple, the failure doubtless re- 
sulting from the use of too small cages. On the other hand, there 
was no difficulty in getting the spring migrants to go to wheat and 
there continue to reproduce throughout the summer from apple 
shoots, even in small lantern globe cages. 
NATURAL CHECKS. 
Like most plant-lice of the genus Aphis, avence is freely attacked 
by various parasitic and predaceous animals, principally insects, and 
doubtless these ^&***=^ 
triticaphis Fitch, Fig. 6.— Aphidius testaceipes ovipositing in the body of the 
(PraOTl) Aphidius SPring § rain - a e his - Enlarged. (From Webster.) 
avenaphis Fitch, and AUotria tritici Fitch, but it is probable that he 
reared these from Macrosiphum granariurru rather than from Aphis 
avence as was supposed by Mr. Pergande. 2 In 1891 F. M. Webster * 
reports rearing Pachynewron micans Howard and (Lysiphlebus) 
Aphidius testaceipes Cresson (tritici Ashmead). The latter species 
(figs. 6 and 7) is the one which ordinarily holds the spring grain- 
aphis (Toxoptera graminum) in check, and doubtless is likewise 
beneficial in preventing undue multiplication in avence. Mr. Theo. 
Pergande 4 reared another species of Aphidius (A. nigriceps Ash- 
mead) in considerable numbers from this aphis. 
Among the predaceous insects Pergande 4 has reared a common 
syrphid fly (Syrphus americanus Wiedemann) (fig. 8) ; the writer 
has reared a species of Aphidoletes from larvae feeding on Aphis 
1 Sixth Rpt. on the noxious and other insects of the State of N. Y., 1865, pp. 98-112. 
2 U. S. Dept. Agr., Div. Ent., Bui. 44, 1904, p. 13. 
3 Ohio Agr. Expt. Sta., Bui. 51, 1894, p. 117, 
i Op. cit. 
