Posted: 16/06/2016 at 21:55
If they have hard shells they probably are one of the wireworms. They are hard to identify and there are several species of click beetle whose larvae are known by this name. Yours aren't the common ones which affect potatoes which is why the pictures you've found don't match.
I think the best way to proceed is cultural and to make sure you remove all plant debris from the area at the end of the season then keep turning the soil over to expose the pupae (which overwinter in the soil) to frost and birds.
This is a US website but has some good tips which may help: