If the leaves are completely missing, it might be something bigger than bugs, maybe chipmunk or ground squirrel? bugs usually leave traces (like partly eaten areas, plus you'd see the bugs, they dont hide from you). If you do see bugs, use very diluted soap and water and spray it on, the bigger critters however you are at their mercy unless you fence the area or maybe take a piss around the area of the plants (not on them!) I dunno, but sounds like a furry critter, I had a chipmunk kill 6 seedlings in one night before, they just disappeared...