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I will soon be refinishing a side of my log home (stripping to bare wood, borate, then stain).  I have noticed that some insect has been boring into the knots of the logs in a few places.  In some areas its just a small hole, but on others it appears it ate out most of the knot.  I do plan on treating the walls with borate, but I am unsure if this will even help since it will probably not be absorbed in the knots.  

Any idea what is causing this?

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Hi Mike,

From the pictures it's rather hard to tell what is causing the damage, but typically borate treatment on clean bare wood is an excellent preventative measure for any of the wood ingesting insects.  Most of the time we see insect holes they are from larvae leaving the log, and there's a small trail of frass below the hole, have you noticed this below any of the holes?

Thanks,

Brian  (brian@permachink.com, permachink.com)

Brian,

Yes I did notice frass on the hole shown in the first picture.  I used a toothpick to scrape it out and see if I could find anything but no luck.  There are no signs of exit holes near the knots.  It appears that is where they are going in, so I am guessing they are attracted to the knots for some reason.

Most likely the female laid her eggs at the edge of the knot, as it would provide the easiest access to a safe place to develop when they hatched. Then the eggs hatched, they burrowed back down into the log (and in this case, down a small fissure in the knot or next to the knot) and developed, then exited through the hole we can see.  Once they reach the flying stage, they're now ready to head off into the great outdoors,  You're borate treatment should prevent a reinfestation.  You may see a few more exit holes appear from this group, but with providing the protection you are with the borate, you should stop seeing them developing a new generation in your logs.  

Thanks,

Brian (brian@permachink.com www.permachink.com)

I dont know that this could be caused by eggs being laid by the knot and then the larvae eating into it.  The knots are usually the hardest area of the log and I would think larvae of whatever insect would have a difficult time eating into the knot- but I could be wrong of course. 

On some of the knots that are affected there is just a single hole, which is quite large for a hatched insect to bore into the knot.  On other knots, its like the whole knot was targeted and hollowed out (there are only a few like this and not shown in the pictures above).  It seems like whatever does it is attracted to the knot for the sap or something. 

Is there something that is attracted to the sap that might cause this?  I have noticed wood wasps, but they usually find old carpenter bee holes and use them.

Hi Mike,

I haven't heard of any of the wood ingesting group of insects (powder post and old house borers are probably the most common) having a preference to tree resin.  Once they hatch, they move to the outdoors and when it's time to lay their eggs, they will utilize just about any fissure in wood to lay their eggs into. The knots will dry at a different rate from the logs, create a gap perfect for depositing eggs, so the resin shouldn't be an attractant for that group at least, but that gap certainly could be.  As to the wood wasps, I'm thinking you're speaking of parasitic wasps, the tiny guys that are sometimes seen flying in and out of other insects holes.  The wasps you see are usually females, and they're looking for an insects' egg to deposit their egg on so it has a food source, so they're a beneficial insect!

Thanks,

Brian (brian@permachink.com www.permachink.com)

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