These are a killer because they can go unseen for a long time and can result in the death of the tree if they are not treated.
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https://laidbackgardener.files.wordpress.com/2017/02/20170210a.jpg?w=720
[image source](https://laidbackgardener.blog/2017/02/10/root-mealybugs-death-from-below/)

They are very similar to the foliage mealy bug except they grow on roots. If repotting is done regularly the roots can be inspected for them and then they can be easily detected. Otherwise they can be suspected if a trees growth seems slow, its leaves wilt and discolor and no other apparent cause can be found. In such cases the roots should be inspected because if its these critters causing those symptoms death of the plant will follow.

Root bound plants will encourage them and also be sure not to introduce them to your environment via new arrivals.

Their white residue can be detected on the sides and bottom of root bound plants.

https://laidbackgardener.files.wordpress.com/2017/02/20170210b1.jpg
[image source](https://laidbackgardener.blog/2017/02/10/root-mealybugs-death-from-below/)

For this one, in most cases, prevention is better than cure.
They can be treated with systemic insecticides but repeated applications will be necessary.

Some success has been had with immersing the root ball in hot water but this is complex and should be thoroughly researched before attempting.