Rampaging cabbage worms

My house has an attached, enclosed space I call a "sunroom" or a "greenhouse" depending on my mood & the season. It makes a great workspace for working on gardening-type activities; it has a dirt floor, it's airy (sometimes too much so) and bright. On both ends it's enclosed partly in glass, and most of the reminder is separated from the outdoors by window screen material, so it's mostly free of mosquitoes. It gets hotter than Hades in the middle of summer because of the fiberglass roof.

Anyway, last year I lost my entire brusselsprout crop to cabbage worms, so I vowed to do something different this year. At first I was going to put row covers over all the plants to prevent the moths from laying eggs, but then I decided instead to put a bunch of my brusselsprout transplants in the "greenhouse". Well, the plants look beautiful for once because they aren't all riddled with worm holes, but the brusselsprouts themselves are these little teeny things, about pinhead-size. I'm guessing the heat has pretty much prevented them from getting to edible size--one of my books states that "cole vegetables are adapted to cool weather, growing best when temperatures are between 65 and 80 degrees F." Maybe they'll pick up when it begins to cool off more during the day?

The four cabbage plants I ended up planting outside in the garden have hundreds of holes and what I think is also a bunch of cabbage worm poop (see pics). I'm sure the worms are having a heyday burrowing into the cabbage heads.