ROUNDHEADED APPLE-TREE BORER. 



19 



apple. Individual trees or blocks of one kind of apple will be at- 

 tacked year after year much more extensively than those of other 

 varieties. Becker (14) concludes from experiments that the borer 

 does not discriminate between varieties and that the preference which 

 is often indicated is merely a matter of propinquity. 



During the present investigations observations were made bearing 

 on this point over a period of five years in the experiment orchard at 

 Elkins, W. Va., As has been stated, this orchard contained only 

 three varieties, namely: 310 King, 341 Grimes, and 341 York 

 Imperial, the block of Grimes occupying a space through the center 

 of the orchard. All the rows of the three varieties abutted impar- 

 tially at one end against an older and heavily infested orchard. 

 There were no conditions within or surrounding the orchard that 

 would appear more favorable for the attack of one variety than 

 another, except that female beetles in entering the orchard to ovi- 

 posit might be expected to alight more frequently on the outer 

 trees. During four of the five years over which counts were made, 

 however, the Grimes in the center were much more severely at- 

 tacked, practically 50 per cent of the 1,639 borers removed from the 

 trees being found in this block. The King trees, although fewer in 

 number, were second in point of attack, and the York Imperial 

 trees suffered least. This ratio of attack, as may be seen from Table 

 VII, was constant for the years 1913, 1914, 1916, and 1917. In 

 1915, which was the year of lightest infestation, the York Imperials 

 were first in point of attack, the Grimes second, and the Kings third. 



Table VIJ.-^-Relative extent of infestation by the roundheaded apple-tree borer 

 of three varieties of apple for a period of five years. 





Variety of apple. 



Year. 



King. 



Grimes. 



York Imperial. 





Number p f 

 of borers. rer cent ' 



Number 

 of borers. 



Per cent. 



Number 

 of borers. 



Per cent. 



1913 



49 



80 



8 



223 



121 



30.3 



33.5 

 8.3 

 35.4 

 23.7 



110 



43 



283 



303 



47.5 

 46.0 

 44.8 

 44.8 

 59.3 



36 

 49 

 45 

 125 



87 



22.2 



1914 



20.5 



1915 



46 9 



1916 



'19.8 



1917 



17.0 







Total 



4S1 



29.3 



816 



49.8 



342 



20.9 







It is entirely possible that the results which are shown in Table 

 VII are accidental, and yet it must be confessed that, aside from 

 varietal preference on the part of female beetles while ovipositing, 

 there is no apparent way of accounting for the almost constant maxi- 

 mum attack of Grimes and minimum attack of York Imperial. 



