Gather a bunch of cigarette butts, and make a nicotine tea. Spray on undersides, and watch those little fookers croak it. Seriously. It's a knockdown agent (instant death) Nicotine is extremely toxic.
If you want to buy something, go for Rotenone or Pyrethrin liquid (both are alkyloid plant defense compounds, derived and concentrated from botanical sources) Rotenone takes about 3 days, but does the job.
Remember about their eggs. You must re-apply twice...? at weekly intervals to make sure you kill all of the hatchlings
I believe all of the above can be sprayed (on vegetables... for eating) right up to harvest, but do your own research.
Alternately, you can try giving them a warm, soapy bath before tucking them in at night. (kidding, that can be effective too, it plugs up their spirocles (breathing holes) but you have to get 100% coverage, and may end up with soapy tasting consumables)
Horticultural oils have the same effect; I would go with that, if available.
My first choice is the nicotine. I smoke, so it's free and easy, and it slaughters those little bastards.