I live in 7b also (but in GA), and I know this reply is years too late, but thought I'd answer it anyway since someone else may be looking for the same thing. Your amaranth bug is striped cucumber beetle. They've been eating my amaranth as well! We have both the striped and spotted cucumber beetles here and the striped beetles seem to outnumber the spotted ones by far. I've picked them off in beetle and also larvae form. They are eating all kinds of things - I keep finding them in the male flowers of my pumpkins so picking off the flowers after fading (making sure no bees are still in them first by peeking) and the squishing the blossom (and bug) before the beetle can escape. Anyway, I've never grown amaranth and the few that I have are over 7 feet tall! Can't wait to see what the blooms look like. Happy growing, everyone!