Considering varnish or shellac as a deterrent for carpenter bees in log cabin: Impact on logs and effectiveness

i have a problem with carpenter bees in my log cabin. for the past five years they keep coming back. i had exterminators treat the house but they keep coming back. someone suggested that i either paint my house or cover the outside logs with varnish or shalak. i do not wish to paint because i like the natural look. can i cause any damage to the outside logs if i use varnish or shalak on it. thank-you joe