all natural so does no harm
That's a very sweeping statement Mt Nasura and I have to disagree. There are many 'natural' but are also extremely toxic: Botulism, Ebola, Cyanide, fire and lots more. If you are just talking about plant products Nicotine and digitalis are both natural plant derived products but are highly toxic to humans.
Pyrethrum, both natural and synthetic (pyrethroid) is, like most 'natural' insecticides, non specific so it will kill bees, ladybirds, lacewings and other 'good bugs' along with the intended victims. The only way to 'do no harm' is to not use insecticide products.
There are very few insecticides , natural or not, that will 'do no harm'.