40 MASS. EXPERIMENT STATION BULLETIN 441 



Sprays to Prevent Scolytid Infestation of Elm Logs. (W. B. Becker.) At 

 Springfield, a number of sprays including different concentrations of DDT 

 (dichloro-diphenyl-trichloroethane) and DDD (dichloro-diphenyl-dichloroethane) 

 were applied once (May 14 to 16) to the entire bark surface of elm logs before 

 scolytids could attack them in the spring. Each test involved 20 to 31 square 

 feet of bark with a maximum thickness between 3/8 and 7/8 of an inch. The per- 

 centages of prevention were based on the number of exit holes found per square 

 foot of bark in the late fall, compared with those in unsprayed logs. In each 

 instance the quantity of spray applied was what the operator estimated to be 

 necessary to thoroughly wet the surface of the bark (58 to 166 ml. per square 

 foot). Scolytus multistriatus Marshi m was much more abundant than Hylur- 

 gopinus rnfipes (Eich.) in both sprayed and unsprayed logs. 



No. 2 fuel oil alone gave 100 percent prevention, as did also orthodichloroben- 

 zene and No. 2 fuel oil, mixed 1 to 8 by volume. DDT solutions in No. 2 fuel 

 oil, at concentrations between 0.0625 and 5.0 percent actual DDT, gave 99.7 

 to 100 percent prevention. A 50 percent DDT wettable powder in water gave 

 74.6 percent prevention at 0.0625 percent DDT, 95.4 percent at 0.125 percent 

 DDT, 97.4 percent at 0.25 percent DDT, and 100 percent prevention in con- 

 centrations containing from C.5 to 5.0 percent DDT. A 25 percent DDT emul- 

 sion in water gave 98.5 to 100 percent prevention in all concentrations used, 

 from 0.0625 to 5.0 percent actual DDT. A 25 percent DDD emulsion in water 

 gave 70.6 percent prevention at 0.06.''5 percent DDD, 95.1 percent at 0.125 

 percent DDD, 94.8 percent at 0.25 percent DDD, 98.3 percent at 0.5 percent 

 DDD, 99.5 percent at 1.0 percent DDD, and 100 percent at 3.0 and 5.0 percent 

 DDD. 



Sprays to Kill Scolytids Breeding in Elm Logs. (W. B. Becker.) At Spring- 

 field, DDT and DDD sprays at the same concentrations used for the preventive 

 applications were applied once to elm logs in an attempt to control established 

 scolytid infestations. Relatively light applications (between 27 and 53 ml. of 

 spraj^ per square foot of bark) were made on June 11 to recently cut elm logs 

 soon after the scolytids attacked them. Beetle emergence commonly starts 

 about the first of August from such logs. Because of the timing of the applica- 

 tions, the spray residues weathered for the longest period of time which would 

 ordinarily be required in any one gro\\ing season. Each test involved 2? to 31 

 square feet of bark of a maximum thickness of 5/8 to 1 inch. In these, as in all 

 other spray applications, the sprayed logs were covered with a single layer of 

 other logs to avoid larval mortality from high subcortical temperatures caused 

 by the rays of the sun. 



There was no apparent relationship between the strength of the sprays used 

 and the number of brood galleries constructed in the various sets of logs. Based 

 on the number of empty exit holes per brood gallerj' in the autumn, the DDT 

 spra^'s gave no control at the lower concentrations and mostly poor control at 

 the higher concentrations. At 5 percent DDT, the oil solution gave 81.5 percent 

 control, while the wettable powder and emulsion sprays gave approximately 54 

 percent control. The DDD sprays gave no control. 



Best results were obtained with the higher concentrations of DDT in oil solu- 

 tion, possibly because of the presence of the oil, which causes mortality by itself 

 when applied in sufficient quantities; and possibly because the DDT was carried 

 down into the bark by the oil solution and so killed beetles before they could 

 reach the surface. Probably the DDT in water emulsion and especially the 



