30 BULLETIN 1107, U. S. DEPARTMENT OF AGRICULTURE. 



EXPERIMENTS IN CALIFORNIA DURING THE SEASON OF 1921. 



The results obtained from the experiments of 1918 to 1920 sug- 

 gested the most promising ones for the season of 1921. Two lines 

 of investigation are involved: (1) To determine why the insect at- 

 tacks the cable, and (2) how to prevent the attack. 



The bark of the wood normally attacked by the beetles is dark. 

 To see if color has any influence on the attack, paints of various 

 colors were applied to sections of wood and sections of cable. 



As beetles appear to be attracted to ferments in the case of the 

 oak tea, wine casks, and vials of alcoholic specimens, several of these 

 liquids were applied to sections of wood and sections of cable to de- 

 termine their influence. In the experiments of 1920 the beetles were 

 not attracted to the cables in cages when alternating current of com- 

 mercial frequency was applied to the conductors, but they did attack 

 the commercial cables in town (Los Gatos) in parallel tests made that 

 year. During 1921 the cooperating telephone company supplied ap- 

 paratus whereby alternating current of talking frequencies could be 

 applied to the cable conductors with a view to determining whether 

 the higher frequencies of the talking current had any influence in 

 producing the attack on the service cables. 



As the results obtained by the use of repellents, poisons, alloys, etc., 

 indicate that the repellents and poisons are useless and that the al- 

 loys are very little, if any, better than the regular commercial lead 

 sheathing, the only hope for protection appears to lie in mechanical 

 protection which can be obtained from greases, asphalt and fabric, 

 rubber and fabric, and zinc or steel sleeves at the rings. Beef tallow 

 seems to be the most promising grease and it was given a thorough 

 test ; tire tape impedes the mining of the beetle considerably, so sev- 

 eral combinations of asphalt and fabric and rubber and fabric were 

 tried; thin steel can not be penetrated, so sleeves of this material 

 were placed around the cable where the rings support it. To make 

 a good practical test of all of these materials a section of cable was 

 selected in an area where past damage had been severe and one ring 

 was treated with tallow, one with fabric, one with a steel sleeve, one 

 left as usual for a check, and so on for several spans. 



As will be seen, these experiments gave definite results but it 

 must be remembered that, because of the periodic and variable nature 

 of the attack (i. e., in different localities at different times) the chance 

 for securing, in service tests during one season, any immediate proof 

 of the effectiveness of these protective measures was not very great, 

 and the service tests will need to be followed up for a period of 

 several years. 



RESULTS OF EXPERIMENTS IN CALIFORNIA IN 1921. 



During 1921 the following experiments with the lead-cable borer 

 were carried on at the Los Gatos Forest Insect Laboratory in the 



