My background if you're interested:
I am very much a beginner to gardening. 38-year-old married man. I
am a Square Foot Gardener (SFG) in Northeast Louisiana.

My question:
I planted, from seed, Brusell Sprouts. They came up and grew to about
3-4 feet tall. They were originally in a raised SFG, a 4'x4'x6" box
about 3' off the ground. That box rotted and the bottom fell out. I
transplanted three of the plants to another SFG box located directly
on the ground. Within a few weeks they were covered with green
catepillars. They were in large numbers and ate through the leaves
and the budding sprouts. I pulled the plants today and discarded them
away from the SFG. My question is not so much about identifying the
worms, but about using pesticides in general on vegetable gardens.
Since I intend to eat what little I grow I would prefer not to use
pesticides, but on the other hand, insects are eating everything in my
two SFG boxes. I have also noticed small black ants, similar to sugar
ants or, as my wife refers to them, **** ants. I see them on my
zuccini and cucumber plants. I don't know for a fact they are eating
the leaves, but the leaves have been eaten on both types of plants by
something.

So, do I let them have the garden or use pesticides? If so, what type
of pesticide should I use?

Thanks a bunch. I need all the info I can get.

Ty