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Member discussion regarding the methods, varieties and merits of growing tomatoes.

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Old July 15, 2017   #1
gorbelly's Avatar
Join Date: Jul 2015
Location: Southeastern Pennsylvania
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Default Halictid bees: essential tomato pollinators or robbers?

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.
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Old July 15, 2017   #2
brownrexx's Avatar
Join Date: Feb 2016
Location: Southeastern PA
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I never really noticed them around my tomatoes. I'll have to look a little closer for those cute little guys. I did see a lot of bumble bees as well as a few honey bees on my bean flowers today though.
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Old July 15, 2017   #3
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Yes halictids buzz tomato blossoms

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Old July 15, 2017   #4
kurt's Avatar
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Location: Homestead, FL
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We have the metallic green beneficials.The burrows they created(thought they where marauders at first)help with nutrient transfer and areation at same time.Cute little buggers,look lke those false mimic flys sometimes.
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Old July 15, 2017   #5
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Location: Newfoundland, Canada
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The little metallic bees are beautiful.
I thought chewing was the fault of carpenter bees.
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Old July 15, 2017   #6
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One thing I noticed, the bumblebee queens are not interested in my tomato flowers. They have come for a look and then zipped off to other flowers. Tomatoes don't have any nectar to offer, just pollen. So I think these queens need the nectar as well.
Just to explain, we had a really late spring, and the first crop of worker bumbles aren't out yet. Last summer the worker bees spent a lot of time on my tomatoes, diligently collecting pollen. The queen meanwhile is out doing her thing as sole forager for their little hive until the first workers are ready to take over.
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