Pest control advice needed

I want to protect my mammillaria collection for next winter.
Till today I never ussed something against mealy bugs and other pests.
Last year I bought COMPO Bi 58  at ELK, the working component DIMETHOAT.
I water all my plants via the bottom, never from the top.
My question, should it be the right way to put the systemic insecticide in the water next time by watering?
Except personal protection are there other dangers I should be aware?

Frederik