Any ideas whether this is some sort of sawfly?

My plot neighbour found it amongst her sweetcorn - the leaves have been shredded and some of the flowers nibbled - I thought it could be slug damage then she found this so I wondered if it's larvae were responsible even though we couldn't actually see any.

Looking through my insect book it looks like rhogogaster viridis. None of the internet hits seem to say it is particularly nasty, for example http://www.plantpress.com/wildlife/o406-greensawfly.php

Thanks Geoff - it's strange that it is on the sweetcorn.

I agree with Geoff on this.

The larvae feed on various herbaceous plants, and the adults prey on other insects. Possibly just a coincidence it was on sweetcorn.