Caterpillar. Did she include any chemicals (like sevin dust) with the flour? It does seem odd that just a little wheat flour would stop the different caterpillars that eat vegetable plants.

I found one reference on the web about this for cabbage plants (an old garden web message actually):

"A friend of mine who raises butterflies says if you lightly dust the leaves with flour the cabbage whites won't lay eggs. They think the plant already has been colonized, and go looking for a fresh one. I have not tried this, so can't say first-hand whether or not it works."

Just plain flour...I'm wondering about "self-rising"...the added baking soda might be an anti-fungal, too?