304 OHIO EXPERIMENT STATION: BULLETIN 332 



Nature of work. — The European elm bark louse colonizes the 

 lower limbs of the host first, but may infest the entire top. At 

 Marietta, Ohio, the writer has observed a number of trees killed, 

 outright by it and many others in a depleted condition. (See Plate 

 LIV, Fig. 3.) Not only does this insect cause positive injury to the 

 host but its copious discharge of honey-dew promotes the profuse 

 growth of an unsightly, sooty mold over the foliage of the host (See 

 Plate LV, Fig. 1) , sidewalks and other objects, and at the same time 

 attracts myriads of flies and other insects. Altogether, therefore, 

 its presence is the cause of much unpleasantness as well as injury. 

 Food plants. — The European elm scale confines its attacks to 

 the various species of elm and of these, the red elm ( Ulmus fulva) 

 is the most susceptible. Other species observed by the writer are 

 the American elm (U. americana) ; and the cork elm. In addition 

 to these, the following species have been reported as hosts : English 

 elm, slippery elm, and Wych or Scotch elm. 



Distribution. — In Ohio, the center of greatest injury is in the 

 city of Marietta, where the magnificent street and park elms in 

 some parts of the city are rather severely attacked. Elms on one 

 or two streets in Columbus are known to be infested and a single 

 report has been received from Cleveland. We have no further 

 records of its presence in Ohio. However, the insect has an ex- 

 tended range of distribution, having been reported from Vermont, 

 Massachusetts, District of Columbia, Michigan, Nevada, California, 

 New York, Maine, Connecticut, Maryland, Washington, New Jersey, 

 Indiana, Canada and Europe. 



Natural enemy. — The twice-stabbed ladybird {Chilocorus 

 bivulnerus) has been recorded as preying upon this scale. 



Control. — Miscible oil used at the rate of 1 gallon to 15 gallons 

 of water and applied in the spring before the foliage starts, in the 

 writer's experience has proven an efficient control measure. In 

 cooperation with the city of Marietta, Ohio, a considerable number 

 of large elms were sprayed March 27 to 30, 1916, with this material 

 in the strength given and the results were all that could be desired. 

 Still further work has confirmed these findings. 



Summer spraying with kerosene emulsion at the time the young 

 are appearing is sometimes advised, but this plan is not satisfactory 

 since several applications are required to kill the continuous pro- 

 cession of young insects. It is also advised as a control measure 

 that the trees be drenched with the hose in order to dislodge and 

 destroy the larvae as they appear, but this treatment likewise has 



