Hello

After growing onions from seed with perfect success for many years, suddenly this year this critter has arrived (see attached image). I first noticed some leaves looked like the slug scrapings... splotches of green missing. I opened a few leaves, finding critter poop and eventually in one plant this fellow... A few of the plants have gone quite brown, though most are ok or just splotchy. The only thing close to this I could find was "onion maggot," but this visitor didn't really look like the portraits I found of onion maggot online. And I do hope not as I believe that affects keepability of the onion, So... fingers crossed... does anyone know what this creature is? What is the prognosis for the crop and how do I avoid his visit next year?

Thanks

Glen