Those were in the soil prolly to begin with.I was specifically referring to bagged soils, not soil open to the elements completely
Root aphids isn't one I have gotten yet, but I have definitely gotten regular aphids, beetles, worms and fungus gnats out of bagged soils that were stored outside unprotected.
Try vermi-composting.... you wanna see some bugs. Then let the vermi-bin over winter and all the bugs are gone. In the early spring the microbes clean up whats left of the insects.
Thats what Id do with bagged soil. Set it beside my vermi bin and add kitchen scraps then a layer of that soil until you used it all up. Then use that vermi-compost in you soil mix.