THE MONTHLY BULLETIN. 63 



reed grass, Phragmites sp., where it remains until fall and then returns 

 to the lives and deposits its eggs; and the hop aphis. Phorodon hum nil. 

 which also attacks the foliage of the plum and then deserts the plum 

 I'm- the hop as a summer host. Mr. L. C. Bragg has been able to trace 

 this species throughout the year in small numbers upon plum at Fort 

 Collins. There are several others of more or less importance which 

 might be added. 



Some "f the species attacking shade trees and ornamental shrubs 

 also have must interesting migratory habits. The louse causing the 

 leaf-cluster gall of the American elm has been repeatedly transferred 

 In the apple by Dr. Patch, Mr. A. S. Maxon, Mr. Baker and, at Fort 

 Collins, by Mr. Bragg. These colonies are indistinguishable from those 

 of the woolly aphis, Eriosoma lanigera, produced from over-winter forms 

 on the apple, so that, while the woolly aphis of the apple is able to live 

 on from year to year without receiving migrants from the elm, and 

 seems to thrive quite as well in regions where the elm is not grown, 

 there seems to lie a tendency to migrate between these hosts to some 

 extent. 



The snowball louse. Aphis viburnicola, is very destructive to the 

 foliage of the Viburnum, and often ruins the flowers, but the offspring 

 of the stem-mother, the second generation in the spring, all desert the 

 snowball and go to unknown hosts which we have not been able to 

 locate. In September and October, the fall migrants come back to the 

 snowball and deposit the yellowish white oviparous females upon the 

 leaves, and by the time these egg layers are half grown, the winged 

 males begin to arrive. The sexes mate, and the females, as soon as 

 they are fully grown, desert the leaves for the purpose of depositing 

 their eggs about the buds and rough places on the bark. 



The Blue and Engelmann spruces and the Douglas fir should never 

 In' placed near each other in parks or upon lawns, as Chermes cooleyi, 

 which produces the cone-like galls at the tips of the twigs of the Blue 

 and Engelmann spruces, deserts these trees during July to go to the 

 needles of the red or Douglas fir, while the form Chermes cooley, 

 var. cowt ui. which develops upon the leaves of the Douglas fir, returns 

 to the Blue and Englemann spruces during the same month and deposits 



11 liu's which hatch iuto the over winter stem-mothers. The following 



spring these stem-mothers produce the brood which locates at the bases 



of the young growing needles just as the buds are opening and cause 



■■i 'lie-like galls. The Douglas fir or spruce, as it is called, in close 



proximity to the other spruces mentioned, is a serious menace to them 



I ause of the large numbers of this louse that it contributes for the 



destruction of the terminal growths early in the summer. 



Cottonwoods are known to serve as winter hosts for the beet aphis, 

 /'< hi i>!i ;<i a* In In , though a portion of the lice always spend the winter 

 in the ground. 



Many of our economic species of the Aphidida lack this alternating 

 food habit completely. The green apple louse. Aphis pond, the black 

 cherry louse, Myzus cerasi, the box elder louse, Chaitophorus negun- 

 dinis, and the dandelion louse. Macrosiphum taraxicis, are good exam- 

 ples. The successful control of the aphis depends largely upon one's 

 knowing the life habits of the species in question, and the enemies that 

 are associated with it. 



