black larvae in onions

Morning all
       just got back from allotment and found most of the plots have onions that have been infected by small black larvae inside the onion skins. symptoms appear to be twisted or browning flags/leaves. and on pulling up the bulb is diseased and starting to rot. Most plots are infected and it does appear widespread.
  keep a lookout.
      Dave
just had a search and found 'allium leaf miner' a nasty little attacker.

The dreaded leaf miner appeared here in Worcester around 5-ish years ago and now mesh netting is essential if you want to grow onions and leeks.