130 MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
The third generation flies from the elms to apple or related plants and 
settles on the leaves, twigs, or water sprouts. Here it produces the 
fourth generation, which is wingless and is the first generation of the 
woolly ‘aphid on apple. In J uly this generation produces another, 
the fifth, which is exactly like the fourth. Some individuals of this 
generation migrate to the roots of the host plant, while others remain 
on the twigs. “Those that remain above ground produce the sixth gen- 
eration, which is winged and matures in September. 
These fall migrants may remain on the apple or related trees until 
late in the fall, but most of them return to elms, where they settle on 
the bark and produce the sexual forms, which are small and wingless 
and do not have functional mouth parts. The female, after mating, 
deposits her solitary egg in a crevice of the bark, where it remains 
until spring, when the stem mother hatches from it. 
The part of the fifth generation which migrated to apple roots may 
remain there over winter. 
Injury to elm by Evriosoma lanigerum consists of the forming of 
rosettes at twig terminals and the curling of leaves. Rosettes are 
formed early in the spring. Leaf curling j is most pronounced early 
in the spring. but may be observed until midsummer. The species may 
be controlled by applying the measures recommended for other aphids. 
The woolly elm aphid (/yiosoma americanum) has much the same 
appearance and lite ale as Ef. lanigerum. It differs, however, in 
that it is known to attack only American elm and to have as its alter- 
nate host the roots of Amelanchier sp. Injury to elm consists of leaf 
curling. For further discussion of the species see Patch (340, 341) 
and Maxson (292, pp. 251-271). 
The woolly elm bark aphid (/7riosoma riley?) is a brown, floccu- 
lent species, about 2 mm. in length, frequently found on elms during 
the summer from New England and southern Canada west to Illinois 
and Wisconsin, in the East as far south as Pennsylvania, and in the 
Southwest to New Mexico. It apparently has no alternate host and 
feeds only on American and slippery elms. Its feeding causes 
knotty growths on the branches similar to the growths caused on 
apple branches and roots by the woolly apple aphid. For further 
information on this species see Patch (340, pp. 260-262) and Hottes 
and Frison (238, p. 354). 
TrinE TETRANEURINI 
These aphids live in true galls on their winter hosts, and are sepa- 
rated into three genera—Colopha, Tetraneura, and Gobiashia. 
Probably the only species in this whole tribe that can be considered 
of economic importance in our eastern forests is the elm cockscomb 
gall aphid (Colopha ulmicola (Fitch)). It is found over most of 
America north of Mexico, wherever its host trees, American, rock, and 
shppery elms, grow. This aphid has six generations annually. The 
first, second, and third generations are passed on elm. The fourth 
generation migrates to grass and the species feeds there through the 
fifth generation. Sixth-generation females migrate back to elm, where 
each ‘deposits one egg, which represents the overwintering stage. 
The appearance of ‘unsightly galls on the leaves, especially on young 
trees and ornamentals, is more important than the actual injury to 
the tree. Full-grown galls range from 0.5 to 1 inch long and may 
