Leafminers, the larvae of a fly that bores its way in between the leaf layers. Generally pose no threat to the plant. If you pinch the affected area between your fingers you can squish him if he is still in there.

Dave

Wow thanks! That never would have crossed my mind. It's on all four plants. Are they common? Any way to deter them?

Not really as insecticides can't contact them to kill and the tiny flies would have to be quickly sprayed right when they land. Finger squishing or just removing the leaves and stomping on them works best. Yes they are common but as I said they are primarily a minor, appearance-oriented issue and no threat to the plant so most don't worry about them.

Dave

As Dave says, if the damage is only occasional, they're no big deal and probably being kept under control by natural predators, etc. in your garden. If you have a severe infestation with extensive damage to a high percentage of your foliage, though, you might consider taking some action.

Insecticides are usually a bad option, as they'll hurt the leafminers' predators while the larvae are safe inside their leaf tunnels, which ultimately can make the problem much worse.

There are species of tiny parasitoid wasps that will parasitize leafminer larvae and help control them. They can be purchased for release, but that can be expensive and pointless if you don't provide a nurturing environment for them. You can attract them and many other beneficial predators yourself by interplanting certain flowering plants that attract and sustain them. (Note that, with herbs, etc., you have to let some of them go to flower to work for this purpose.)

Also, leafminers pupate in the soil, so application of predatory beneficial nematodes should help control them (as well as many other pests such as flea beetles, etc.).

The leaf miners aren't a problem on tomatoes at all, so you should not be concerned about it, however they are a big problem for sunflower and artichoke.

It seems 'bt' is recommended to use against them. You can use yellow sticker traps which attracts those small flies and gnats, but I rather not because there are too much lizards around in Florida.

They can be a big issue on leafy brassicas as well.

I hate these things. Found them on my dwarf lemon tree in early fall and they were focusing on and ruining all new growth.