December, '15] BALL: estimating number of grasshoppers 525 



great many trees, and this could be seen for a long distance down the 

 nursery rows. In the rows treated with carbolineum or its emulsion 

 no sawdust could be seen and the trees were vigorous growers, the 

 trunks shoTsdng a beautiful brown color but not an indication of borer 

 work. The kerosene emulsion had no appreciable effect, nor did it 

 injure the trees, though it was applied in large quantities. The 

 treatments applied and results obtained may be quicklj^ ascertained 

 by consulting Table II. Kerosene emulsion applied pure in the fall 

 seems to have had some effect but one cannot safely draw conclusions. 

 Thirty per cent infestation is high, though the average number of 

 larvae per tree is a minimum. The carbolineum applied pure and its 

 emulsion gave almost absolute control and seems to me a very simple 

 and effective means of control under nursery conditions. 



Table II. Cryptorhynchus lapathi Linx. 



Treatment 



When 

 Applied 



Number 

 Trees 



Examined 



Number 

 Infested 



Larv.'B 

 per Tree 

 (Average) 



Not 

 Infested 



Per Cent 

 Infested 



Kerosene emukion (pure) 



Dec. 4, 1914 



20 



June 28, 1915 



6 



1 



14 



30 





Apr. 9, 1915 



25 





16 



2.25 



9 



64 



Carbolineum 



Dec. 4, 1914 



20 





0 





20 



0 





Apr. 9, 1915 



27 





0 





27 



0 



Carlx'lineum 



Dec. 4, 1914 



20 





0 





20 



0 





Apr. 9, 1915 



50 





0 





50 



01 



Check 





116 





56 



2.4 



60 



48.3 



The cost of these various treatments has not been ascertained. 

 The carboUneum costs at retail prices 11.00 per gallon, and one gallon 

 should treat at least one thousand to fifteen hundred trees. I am 

 planning to carry on this work on a large scale during the coming year 

 and shall probably treat twenty to thirty thousand trees. In this way 

 the cost of treatment may be determined under commercial conditions. 



ESTIMATING THE NUMBER OF GRASSHOPPERS 



By E. D. Ball 



In most of our published works on injurious insects such terms as 

 abundant, swarming, numerous and common are used to designate the 

 number of individuals concerned in a given attack. 



The writer has found that in codling moth work the exact number 

 of worms per tree and per hundred apples, either present or to be antic- 

 ipated from previous counts, are vital facts in the problem of control, 

 less than one or two worms per hundred apples indicating a good con- 

 dition — more than the number requiring additional control measures. 



^ One half grown larva was found in July, evidently due to lack of thoroughness 

 in treatment. 

 2 



