214 MONTANA EXPERIMENT STATION. 



APPLE LEAF=APHIS. 



. Aphis pomi DeG. 



A few years ago practically all the accounts of plant lice on the 

 foliage of apple trees were written of one species, which was known 

 under the scientific name, Aphis mali Linn. Dr. John B. Smith, of 

 Rutgers College, New Jersey, and others, had noticed that accounts 

 of the insects in other localities did not agree with their own observ- 

 ations, but not until Prof. E. Dwight Sanderson* published the results 

 of his investigations, was it made clear that, instead of having one 

 apple aphis in the United States we have several. 



We have at least two species in Montana, but one of these, the 

 Apple Leaf-aphis, is far more common than the other and is respon- 

 sibie for practically all the injuries. 



CHARACTER AND EXTENT OF INJURY. 



No fruit pest has been more frequently inquired about in the let- 

 ters to this Station than has this aphis. These letters, as well as the 

 writer's experience in various parts of the state, show conclusively 

 that the species are very troublesome and at times a very injurious 

 pest. It is universally felt that as a rule young trees are much more 

 susceptible to attack than trees in bearing. The writer's field notes re- 

 cord one notable exception to this in the case of a large orchard in 

 Flathead county, composed of trees which had been in bearing for 

 many years, which were so badly infested as to have the foliage with- 

 ered, and the fruit undersized and poor. 



A prominent characteristic of the work of the aphis is the curling 

 of the leaves. In this respect there is a marked difference between 

 the effect on the tree of the work of this species and of "Fitche's 

 apple aphis," which, on the whole, is more common in the United 

 States. In curling, the deformed leave usually takes a characteristic 

 shape. The surface becomes irregularly raised and the whole leaf curls 

 bringing the under surface inside and the upper surface exposed. The 

 tip of the leaf rests upon its base, not in the middle, but to one side 



♦Thirteenth Annual Report of the Deleware College Agricultural Experiment Station. 



