The good - PLUS ...

The badandugly.
On the one hand we have … … …
"The beneficial hover fly larvae begin feeding on the aphids as they hatch. After spending several days eating aphids, the hover fly larvae attach themselves to a stem and build a cocoon. They spend 10 days or so inside the cocoon during warm weather, and longer when the weather is cool."

On the other hand … … … 
I am very unkeen on Slug pellets, and try for "Safe " ones where possible, and tend to rarely use them.
HOWEVER, when you find another recently mentioned mad mob of  marauding molluscs have wrought havoc on one of your Brussels,
(Or, to put it another way, about 12 % of my stock) I feel it's high time to take action?
I think I stopped counting corpses as I neared 30.
:¬(
There are, actually, two plants the same age in shot; one above & one below the leaky hosepipe.