Either but most likely both. As they can be an issue even in gardens without mulch. Bare soil plants in mine that I hadn't mulched yet since it was still so cool are covered with them too. Like ticks and other damp, cool soil lovers it is a record year for them unfortunately.

Dave

After my post I went out and looked at the bale of straw, just covered with the beasts. I'm guessing they were in the cool interior and I opened Pandora's box. The whole thing went in the city yard debris for compost. My pile will never kill them.

Interestingly, last year I grew tomatoes in a straw bale with reasonable success and never had a flea beetle problem. Go figure! Time will determine how bad they get. Now if I could just get my carrots going.

Pat