RE: December Garden Journal Challenge

My wife is a big fan of Bak Choi being from the Philippines, her culture is heavily influenced by it. I remember we grew it once and got decent harvest here in Australia. But we found we were always under attack from caterpillars, aphids and snails. What suggestion would you make to overcome these hungry insects whom also love Bak Choi? I can repel the snails but it's the dredded caterpillars whom do the most damage!