14 SOME INSECTS INJURIOUS TO FORESTS. 



found growing among- bsidly damaged ones, a nmeh larger percentage 

 of the product would resist attack and, by continuing this method of 

 selection and breeding, imnume varieties could in time be established. 

 There are, however, some serious difficulties to be overcome by this 

 sexual method, especially that of cross-fertilization and variation and 

 the very long time required to get definite verified results. 



FROM ROOT CUTTINCJS (asEXUAL METHOd). 



It has since occurred to the writer that insect-resistant varieties 

 might be secured by a much shorter method, namely, that of propa- 

 gating from root cuttings and possibly from twig cuttings. By this 

 simple method of asexual propagation a large number of ofi'spring, in 

 every respect like the parent stock, may be secured at once for the 

 starting of experiments to deternune whether or not the asexual prod- 

 uct of trees which have not been injured by the borer will produce 

 plantations equally as immune. The writer's experience in the estab- 

 lishment of improved varieties of timoth}^ by this method leads him to 

 believe that insect-resistant varieties of locust can be established. If 

 so, the principal difficulties in the problem of preventing losses from 

 the ravages of the borer will be solved. 



It should be mentioned in this connection, however, that it is possi- 

 ble that the borer, if deprived of the trees which are most attractive 

 to it, ma}^ graduall}' adapt itself to the more resistant ones and l)ecome 

 more or less injurious to these, and that other insect enemies may be 

 troublesome. There will be so many advantages, however, in propa- 

 gating from healthy vigorous stock that, in the writer's opinion, the 

 matter should receive immediate attention, and selection and propa- 

 gating experiments should be started at once. The success of the effort 

 will depend largely on the proper selection of imnume trees from the 

 worst infested groves or sections rather than from those growing in 

 partially immune localities. 



Domestic animals and cultivated plants have been improved by 

 selection and breeding to meet almost every need and requirement of 

 man, and it is well known that some races and varieties are much less 

 susceptible to injury by disease and enemies than are others. It 

 is reasonably certain, therefore, that the locust will not be an excep- 

 tion, but that it will yield to the breeders' manipulations and may be 

 made to produce insect-resistant varieties and forms specially fitted 

 to suppl}' tlie different needs of conmiercial planting, shade, and 

 ornament. 



In the meantime, much of immediate practical value and importance 

 may be accomplished by following the suggestions herein contained 

 for the direct control of the insect in extensive plantations and in 

 natural forest growth. 



