Bug damage/ corking on Trichocereus

[terraferma]

Here are some pics that a family member has sent me. Can anyone identify the problem he's got?

 

He told me he's had problem with thrips on some of his plants not so long ago. Does that look like damage caused by thrips to you?

[Kykeion]

Glancing at the photos before reading your text my thought was thrips and/or spider mites.  So yes, it does look like it could be trip damage .

 

It also looks like the twine may be causing problems. Either it was the source of the pests or it is serving as a hiding area for them. It is also possible that the twine was treated/contaminated with something that the cacti don't like.

[terraferma]

Thanks for the info, Kykeion