What pest
 

Hi there,
hopefully someone out there can offer us some advice to someone very naive
in the ways of gardening. We planted a bunch of Marigolds in our garden.
They were getting munched down quite badly, so that only a dry stem was left
sticking out the ground. Initially I thought it was slugs, but after using
nemaslug, a few more have suffered the same slug. The stem appears to have
beeen hollowed out from the inside. I seem to have read about a pest that
does this, but can't remember what it was... I would appreciate any thoughts
or advice

Thanks
Bruce