Beet leaf miner

I've grown beetroot and chard under netting for a few years now, ever since beetroot seedlings were getting massacred at the first leaf stage and chard made inedible. The beetroot go in the same bed as the carrots and get covered with enviromesh. Scaffold netting seems fine enough to keep the leaf miner out so my chard is under that and hasn't been touched at all so far. The chard I plant in the greenhouse in September/October is never affected though.

The eggs look like really small grains of rice and they lay them in groups. They're really well stuck on to the leaf and not easy to rub off like caterpillar eggs.