6 BULLETIN 1223, U. S. DEPARTMENT OF AGRICULTURE, 



Trees which have been attacked for a number of years by this 

 insect, if they do not die, finally seem to develop a certain amount 

 of resistance to its injury. The history of this scale insect through- 

 out North America has been much the same. It causes much con- 

 cern to the owners of shade trees for a number of years after mak- 

 ing its first appearance, and then seems slowly to lose its grip upon 

 the trees until it causes a much smaller amount of damage. This 

 is especially true in sections of the Eastern States and Canada, 

 where less attention than formerly is now paid to this once dreaded 

 insect. 



FOOD PLANTS. 



The recorded food plants of the European elm scale in the United 

 States are English elm (Ulmus campestris), Scotch or Wych elm 

 (U. scabra), European species, and white or American elm 

 (U. americana), cork elm (U. racemosa), and slippery elm (U. 

 fulva), American species, and their varieties. Probably all species 

 of elms are subject to attack by this insect, although some have not 

 yet been recorded as host to it. 4 



In 1895 Lintner, then State entomologist of New York, collected 

 immature specimens of a scale insect on willow at Loudonville, 

 N. Y., which were determined at that time as the European elm 

 scale. This determination has since been corrected and those speci- 

 mens have now been identified as a species of Eriococeus. 



Signoret (19, p. £1), a French entomologist, has stated that he 

 collected Gossyparia spuria on alder in France. Lindinger (12, p. 

 54-, 64, T£%, 159, 338), also a European entomologist, gives the fol- 

 lowing hosts in addition to elm: Acer sp., Alnus sp. (very prob- 

 bly Signoret's record) , Corylus a.vellana, Fraxinus excelsior, and 

 Viscum album, all European records. From the fact that the Euro- 

 pean elm scale has not been found on any of these hosts in America, 

 the writer is inclined to believe that some related species has been 

 confused with it. At any rate there are no records of the European 

 elm scale occurring on anything except elms in America. The 

 writer has seen both alders and willows growing with their branches 

 interlaced with those of infested elms, yet not a scale could be 

 found on either of them. One specimen of Zelkova acuminata, 

 which belongs to the elm family (Ulmaceae) , has been seen growing 

 near a large number of infested elms, but no infestation was 

 apparent upon it. 



DESCRIPTIONS. 



EGG (PL. I, A). 



Oval in outline, twice as long as wide, 0.36 by 0.19 millimeter. Color bright 

 yellow; surface smooth and shiny. Eyes of larva visible as two black spots 

 through the egg membrane. 



4 Aside from- the European elm scale the principal insect pests of the elm in the West 

 are the carpenter worm, Prionoxystus robiniae Peck, which bores into the trunks and 

 main limbs, often killing large branches and occasionally whole trees ; an aphid, Myzo- 

 callis ulmifolii Monell, and a leafhopper, Empoa ulmi L., both of which suck the plant 

 juice from the elm leaves and produce an abundance Oif honeydew. They are sometimes 

 worse than the elm scale in this respect. 



The elm leaf-beetle, Galerucella luteola Miill.. is probably the worst enemy of the elm 

 in the East, where it defoliates a great number of trees every year. It has also been 

 introduced into the West, having been reported several years ago from Portland, Oreg. 

 This has not yet become a serious pest in the West, but may in the near future. 



