from another forum.............I think those are root aphids...... do you have any fliers? I had them and it really stalled some plants and showed up like Mg deficiency. I sprayed and soil drenched with azamax, after some pyrethrium spray on the plant and soil. 3 days later I saw every stage of life from eggs, those, and fliers dead everywhere in the cabinet. i thought the fliers were gnats at first, gnats and Mg def) I had to transplant a few days later and they've really taken off.
can't find any bugs for a week now just bigger plants. If this is the case you might look at the aza products.