476 



JOURNAL OF ECONOMIC ENTOMOLOGY 



r^^oi. 8 



After witnessing encrusted scale insects surviving a bath ten times 

 normal strength, or others still alive and growing after three biweekly 

 sprayings of a stronger than usual sulphur-lime, one cannot agree with 

 the statement that the prevalence of the insect is due to faulty appli- 

 cation. It must be due in part at least in these cases to an inherent 

 vigor of the insect to withstand the toxic effects of the spray. To 

 determine the range of individual susceptibility to this and other sprays 

 and to ascertain the proportion of immune individuals, and thus to 

 measure the biological difference in scales from several localities, the 

 Washington Experiment Station some years ago instituted a series of 

 experiments in which identical solutions were spraA^ed at selected 

 places. The results of the tests of 1913 were reported at the Atlanta 

 meeting of the Association of Economic Entomologists and were pub- 

 lished in the Jouenal of Economic Entomology for April, 1914. 



It is the purpose of this paper to announce the results obtained this 

 year, which, while corroborating the previous seasons' tests, show 

 even a greater range in susceptibility among the scales from various 

 localities. 



The plan of the experiment took as a standard three-degree factor}^- 

 made sulphur-lime, comparing this with both stronger and weaker 

 sprays and checking against oil emulsions as well as against no spraj^- 

 ing at all. The sulphur-lime concentrate tested thirty-four degrees 

 Beaume and was made at the Petrie plant at Clarkston. This was 

 diluted for tests at five degrees, three degrees and two degrees. Thom- 

 son's Orchard Brand oil emulsion at 5 per cent strength was used as 

 in the tests of the two preceding years. Owing to difficulty in emulsi- 

 fying crude oil with the liquid soap at hand the results with this insec- 

 ticide were not promising and will be neglected in the present discus- 

 sion. A sulphur-soda spray known as Soluble Sulphur also was used 

 at each place made up in concentrations equivalent to the sulphur- 

 limes used. For comparison w^ith the tests made in preceding years 

 the spraying was done at Clarkston, Walla Walla, Sunnyside, North 

 Yakima and Wenatchee, although different trees w^ere used at all the 

 places except Sunnyside. Apples were used throughout the experi- 

 ments. 



The applications were given just previous to the swelling of the 

 buds, a narrow cylinder bucket pump and Bordeaux nozzle being em- 

 ployed. The selected branches were more than drenched with a driv- 

 ing spray so as^to avoid the possibility of missing any individuals. 

 Whenever there was any danger of the spray drifting to other selected 

 branches the parts being treated were isolated by large cloth sheets 

 previously rendered water-proof by immersion in a gasoline solution 

 of mutton tallow. 



