CONTROLLING INSECTS IN LOGS BY EXPOSURE TO 

 DIRECT SUNLIGHT 



By S. a. Graham 



Assistant Entomologist, Department of Agriculture, University of 

 Minnesota 



The protection of logs, left in the woods over the summer season, 

 from the attack of wood-destroying insects is one of the difficult prob- 

 lems, facing the forest entomologist. Several suggestions for the con- 

 trol of the pests concerned have been made from time to time and 

 have proved more or less successful. The most effective method 

 recommended, that of immersion of the logs in water, is a matter of 

 common practice in handling coniferous species. The loss through 

 water logging will not permit this treatment for most hardwoods and, 

 since it is not always possible to get even the conifers into water, we 

 must often resort to other control measures or stand very material 

 losses. Barking the logs and shading with brush have been recom- 

 mended and have been used in practice to a limited extent. 



Exposing the logs to direct sunlight is the latest method suggested 

 for controlling these insects. A brief article by Craighead ^ describing 

 the effects of solar radiation upon logs has appeared during the past 

 year. Working with ash logs in several localities in the South, he found 

 that the upper side of logs lying in full sunlight often reached tempera- 

 tures above the fatal point for insects. On the basis of these findings 

 he recommends weekly turning to protect logs from wood borers. He 

 observed temperatures under the bark of logs which exceeded air 

 temperature by as much as 60° (F.), depending upon the locality, 

 condition of the sky, and angle of the sun's rays. 



From work being conducted in Minnesota it appears that there are 

 a number of other important factors influencing the subcortical tem- 

 perature of logs which Craighead has failed to mention, such as color, 

 structure, thickness and surface of the bark, air currents, evaporation 

 from the surface layers of the bark, and proximity to other absorbing 

 or radiating surfaces. It therefore seems desirable to publish this 



' F. C. Craighead. Direct Sunlight as a Factor in Forest Insect Control. Proc. 

 ol" the Ent. Soc. of Washington. Vol. 22, pp. 106-108. 1920. 



512 



