324 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



is tliv, and the div bark is not attacked by insects which are de- 

 structive to the wood. This makes it practical)le to cut the trees any 

 time <hirin<r the summer. 



The lead cable borer. — Studies and experiments at our Held station 

 at Los (latos, Calif'., and East Falls Church, Va., relative to dama'^e 

 to lead telephone cables by a wood-b()rin<^ beetle have been continued 

 with prospects of solvinfj the problem. The telephone companies have 

 furnished a \\xv\ic amount of material and •rone to considerable ex- 

 pense to ofl'er facilities for the investij^ations. 



('hemical treat nient.s of wood. — Kx])eriments in chemical treat- 

 ments of commercial wood products to prevent insect damage have 

 l)een continued, and the results so far indicate that a number of 

 kinds of Xortli American woods can be treated so they may be safely 

 u.sed in tropical coinitries, where otherwise serious dama<:;c would 

 be caused by termites. 



Water !<iibiner</cnre and sun-cuiing treatment of crude products. — 

 Kxperiments (hirin<r the year have shown that a combination of 

 water submergence and sun curing' Avill prevent injury by wood- 

 boring insects to saw logs that must be held over during the spring 

 and summer months. 



Seasonal cutt'iiKj. — 'J'he extensive experiments in seasonal cutting 

 of timber to determine the best time to do the work liave been .com- 

 pleted, and the results show that there are optimum times for the 

 cutting of different species of trees to avoid insect da'iiage to the 

 bark and Avood. This is of especial importiince in connection with 

 material for log houses and rustic work. 



The host selection 'principle. — Continued experiments relative to 

 the Hopkins host selectitm ])rincip]e tend to establish the fact that 

 insects which attack a number of sjjecies of trees or plants prefei 

 to continue their attack on the particular species in which they have 

 bred for a few seasons. This knowledge is of special economic im- 

 portance in connection with control work against certain insects. 



Shade trees. — The work on insects affecting shade trees and orna- 

 mental hard}' shrubs has been limited largely to correspondence, 

 owing to the lack of funds to be devoted to this line of work. There 

 is a constantly increasing deuiiind for information on the subject, 

 and some special iuAestigations have been conducted at field sta. 

 tions at Los (iatos, Calif., and Colorado Si)rings, (^olo. There is 

 urgent need of the extension of this Avork. 



I'he bioclimatic law. — Much time during the year has been de- 

 voted by Dr. Hopkins to the continuation of investigations relative 

 to the application of the principles of his bioclimatic law to entomo- 

 logical and agricultural research and eccmomic practice, in Avhich 

 notable progress has been made toward establishing the !:)rinciples 

 involved and the development of systems of applying them in the 

 solving of problems of utmost importance to humtm interests. 



Kecent studies have shoAvn that the law applies to the continental 

 areas of the Xorthern and Southern Hemispheres, and that it gives 

 a reliable basis for the classification of the major and minor zones 

 of the world in which similar conditions of climate and life may 

 be expected to occur, thus giving a new basis for a more scientific 

 consideration of the problem of the introduction of useful plants 

 and animals and the prevention of the introduction of pests from 



