Are these plant parasites?

G'day all! I was hoping somebody light know what this is, and how to get rid of it/them?
At the moment they are small enough to sit out in the sun with some foliage and not really be seen by humans.
BUT... They are large enough for some sort of bug to begin smashing my plants!
Would pyrethrum fix or help?
The plants are about 4 weeks old, are outside during the day, and under lights when it's dark outside.

Myself I wouldn't start treating for bugs I haven't seen or seen more evidence of than what you show. Where are you? What insects are where you are? Moths and butterflies?

Diatomaceous earth sprinled liberally over the top of the medium discourages crawlers like caterpillars. A saucer with warm beer in it at ground level does slugs and snails in.

I live in Australia mate.
I talked to our garden lady at work, she reckons it might be "scale". Mind you, I was referring to my missus tomatoes . I have a bit of a microscope for my phone, and got this picture of whatever it is.
So I bought this for it.
I have doped her to the eyeballs with this stuff, upon the surface and underneath. Now we wait and see.