282 OHIO EXPERIMENT STATION: BULLETIN 332 



Distribution. — The San Jose scale occurs in every county in 

 Ohio and in every important fruit-growing district in the United 

 States. Its native home is China, from which it was introduced 

 into the United States on nursery stock, first becoming estabUshed 

 in San Jose, Cal. The principal means of spread from locality to 

 locality is by the transfer of infested nusery stock. Locally it is 

 distributed by the young larvae drifting in the wind and by their 

 clinging to moving birds, insects, floating spider webs, etc. 



Natural enemies. — During the last two or three seasons natural 

 control agencies have been exceedingly active in some sections of 

 Ohio, and as a result of their work the damage by scale has been 

 greatly decreased. Indeed, in some sections the scale has almost 

 disappeared. It is to be hoped that the law of nature's balance is 

 asserting itself and that we are entering an era in which the San 

 Jose scale will not be the menace it once was. 



It is not known definitely just what control agencies are re- 

 sponsible for the present changed condition, but indications point 

 to unusual activities by internal Hymenopterous parasites. The 

 known list of these tiny wasp-like creatures is larger than one at 

 first would suppose. The following have been reported : Apheli- 

 nus fuscipennis, A. mytilaspidis, Aspidiotiphagus citrinus, Anaphes 

 gracilis, Physcus varicornis, Prospaltella aurantii, P. perniciosi, 

 Ablerus clisiocampae and Rhopoidens citrinus. Several lady 

 beetles are known to attack the San Jose scale. The two species 

 most useful in Ohio are the tiny, coal black species Microweisea 

 misella, and the twice-stabbed lady bird, Chilocorus bivulnerus, 

 which is a larger insect, coal black in color with a red spot on each 

 wing cover. 



The writer observed at Ironton, Ohio, an instance where cur- 

 rants had been rid of an attack of San Jose scale by the work of 

 a red fungus, Sphoerostilbe cocophila. 



Control. — Under urban conditions perhaps the most generally 

 satisfactory control measure consists in spraying the infested trees 

 or shrubs with soluble or miscible oil, since this material does not 

 stain the paint of buildings as do the sulphur sprays. The oil is 

 diluted at the rate of 1 part to 15 parts of water and is applied in 

 the spring before the buds break. Where danger of staining does 

 not exist, any of the various sulphur sprays except the self-boiled 

 may be used with good success. 



It should be remembered, as with all spraying for scale insects, 

 that thoroughness of application is absolutely essential to success. 



