Halictid bees: essential tomato pollinators or robbers?

[gorbelly]

I've been noticing that, while bumble bees will visit my tomatoes, they prefer my peppers and eggplants among my solanaceous veg. The one pollinator I see constantly and in large numbers on my tomatoes are the little sweat bees/halictid bees. I see 2 dominant kinds. One is a metallic green. The other is a shiny black. The black ones are a little smaller, but both are pretty small as bees go.

The bees are obviously too small to release a lot of pollen by sonicating the way the larger bumble bees do. I notice them chewing on the anther cone very diligently, then sonicating a bit (or that's what it looks like to me--I'm guessing if that's what's happening, I can't hear it because they're small and the frequency is too high). I read somewhere that they chew through solanaceous plants' enclosed anthers to reach the pollen inside, and I've read that some halictids are buzz pollinators, but I haven't been able to find anything that confirms that they buzz pollinate tomato flowers specifically.

The marks left by the sweat bees are more of generalized bruising/chewed up area at the very tip of the anther cone, very different from the discrete "bite marks" left by bumble bees further up on the anther cones. Also, I see a lot of anther cones that are so chewed up that the stigma becomes exerted even if it normally isn't an exerted stigma variety, and I think the sweat bees are mostly responsible for this. I don't mean normal browning as blooms age--many of these are relatively recently opened blooms.

I'm thinking that the sweat bees are actually the species that do most of the pollination of tomatoes. They're easy to miss because they're small and quiet, but they show an enthusiasm for tomato blooms that not even bumble bees have. Once I start noticing them, I see them in large numbers everywhere.

At first, I wondered whether they were "robbers", chewing through the anthers, taking the pollen, but not really contributing to distributing the pollen. Then I wondered whether they work in synergy with larger buzz pollinators like bumble bees by opening up the anthers and making it easier for pollen to come out. I also think maybe they contribute a lot to cross-pollination in a way that even bumble bees do not because they expose the stigma of flowers with their chewing. And we know that nature loves cross-pollination and that tomato flowers that are cross-pollinated tend to set fruit more reliably and produce bigger fruit.

But after seeing so many of them buzzing their wings while chewing, I think maybe they're also successful buzz pollinators, too--they just need to open up the anthers because of their small size and weaker vibrations.

Anyway, these are just some thoughts I had that might interest those of you who like insects and other garden critters.

I do notice that the blooms that look like they chewed on them a lot are almost never the ones that suffer blossom drop.

I tried to research this online but found very little information on sweat bees and their role in pollination. I may have to do more focused research in a library or something to find out more. If anyone knows of good sources of information on this, I'd really appreciate a tip.