It's so depressing when all your new lovely seedlings are destroyed in a couple of days isn't it?
I planted Rocket, Radishes, Mustard and a few other bits and bobs in July last year and they were decimated by flea beetles. Derris worked a bit, but I didn't like using it. In the end I planted again under a fleece cloche which worked very well and resulted in very attractive looking 'clean' plants! This year I will use a bit of the fine enviromesh over a frame, which I am hoping will work ok.
I did try the 'sticky piece of wood' trick a la Two Sheds, which is mentioned in Geoff Hamilton's book also - unfortunately there were so many of these d*** beetles it didn't work for me. I'm glad someone has had success with it though. I did want it to work for the fun factor!
I thought it might just have been a problem in the warmer summer months so had been planning to plant such things earlier or later to miss the hot dry weather, but if they are already attacking your crops, that's put paid to my theory.
Good luck, hope you find a workable solution.