24 PROTECTION OF PLANTS, 1915-16 



APPLE PLANT LICE AND THEIR CONTROL 



Dr. Robert Matheson, Cornell University. 



There are three species of plant lice, the green apple aphis {Aphis 

 pomi, DeG.), the rosy apple aphis (Aphis sorbi, Kalt.), and the grain aphis 

 (Aphis avenae, Fabr.), which attack and injure the foliage and fruit of apple. 

 Of the three species the grain aphis rarely does any particularly serious 

 injur>', whereas the other two species frequently become enemies of the 

 first magnitude. These plant lice have come to us from Europe and they 

 have been present and reported as injurious ever since the latter part 

 of the first half of the nineteenth century. At the present time, they are 

 widely distributed throughout North America and occur wherever the apple 

 is grown. In order to present the subject matter as logically as possible 

 I shall treat each of the species separately. 



The Grain Aphis 



(Aphis avenae Fabr.) 



This aphis uses the apple only as one of its host plants, chiefly for the 

 deposition of its eggs and the developing of a few generations in the early 

 spring. The overwintering eggs are found mingled with those of the other 

 two species, though more generally distributed on the larger branches and 

 even the trunks of the smaller trees. The eggs appear as small, oval-shaped, 

 black objects. 



The eggs of this species hatch earlier than those of the other two, 

 at Ithaca at least eight or ten days earlier (Apr. 13, 1915). At this time the 

 buds do not show green and the lice wander about a few days endeavouring 

 to penetrate into the tips of the swelling buds. The length of time during 

 which the eggs hatch was not determined. The stem mothers mature 

 during the last days of April and the first week of May, at the time the blos- 

 som buds show pink. They are easily distinguished from the other two spe- 

 cies. The grain aphis is bright green with three narrow longitudinal bands 

 of darker green on the abdomen. This character will readily separate this 

 species from the other two most liable to be confused with it. 



