236 MAINE AGRICULTURAL EXPERIMENT STA'J'JOiN. lc;i2. 



the significance of the recent discovery * that the elm leaf curl 

 harbors the "wolf in sheep's clothing'' is an important factor to 

 be taken into consideration in dealing with the woolly aphid of 

 the apple. 



While working over some elm aphides several winters ago I 

 found that I was unable to separate on structural characters 

 certain collections of Schisoneura americana (causing and in- 

 habiting elm leaf curl) from certain collections of Schisoneura 

 lanigera (the troublesome woolly aphid of the apple). Collec- 

 tions could be selected which showed apparently significant 

 antennal differences but others could be selected which could 

 only be separated by reference to the tree from which they had 

 been taken. Notice in this connection antennal figures 449 to 

 459. (As a study of the antennal variation in 1,000 individuals 

 of this species is nearly ready for press,- further discussion of 

 this point is not necessary here.) 



This circumstance brought no real conviction, for lanigera 

 (described in 1802) has been under economic surveillance for 

 more than 100 years and Riley (1879) gives descriptions of 

 seven consecutive generations of americana, froin the stem 

 mother to the true sexes inclusive, all on the elm. On the other 

 hand spring and return migrants of americana had been re- 

 corded from the widely separated localities of Idaho (Aldrich 

 1901), Kansas (Sanborn 1904) and Maine (Patch 1910) and 

 their summer residence was still a mystery. Moreover- the 

 overwintering of lanigera on the apple roots was, though con- 

 fu.sing, no argument against another host for the winter tgg, 

 for, as was shown for the Alder Blight, the all year presence of 

 apterous forms on the alder was coincident with a migration to 

 the maple for the deposition of the true sexes and the winter 

 eggs. (Bulletin No. 195 of this Station). 



Field observations were made during two seasons with this 

 problem in mind but brought no solution, the summer occur- 

 ence of rileyi which I consider to be an elm bark form of 

 americana (See Me. Sta. Bui. 181, p. 237) complicated the 

 situation, while the fact that both hosts were under out door 

 conditions, not easy of control, left too much roorn for doubt. 



This past winter, however, material under control conditions 

 was secured by raising seedling apples in the greenhouse where 



* Science, Vol. 2>^, p. 30. "Elm Leaf Curl and Woolly Aphid of the 

 Apple." 



