. Bulletin of the Department of Agriculture. Agriculture; Agriculture. 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 m
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. 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 Fig. 6.—Aphidius testaceipes ovipositing in the body of the spring grain-aphis. Enlarged. (From Webster.) NATURAL CHECKS. Like most plant-lice of the genus Aphis, avenw is freely attacked by various parasitic and predaceous animals, principally insects, and doubtless these are responsible for the usual control of this pest. Among the in- ternal parasites, Fitchx has r e - corded Toxares triticaphis Fitch, (Praon) Aphidius avenaphis Fitch, and AUotria tritici Fitch, but it is probable that he reared these from Macrosiphum granarium rather than from Aphis avence as was supposed by Mr. In 1894 F. M. Webster * reports rearing P achy neuron 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. Pergande4 reared another species of Aphidius {A. nigriceps Ash- mead) in considerable numbers from this aphis. Among the predaceous insects Pergande 4 has reared a
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