Here you go - a great article from UC Davis on both organic and chemical controls (linked below). If there are just a few you can usually just pick them and squish them while getting rid of the source of the infestation - the trees. You can also spray them off the seedlings with a misting bottle. Using a small fan on the seedlings not only benefits the stem development but helps control the aphids.

And this article is from North Carolina State and is specific to controls in the greenhouse. It's recommendations seem a bit drastic to me - destroying plants etc. - so I'd sure try the less drastic approaches first.

Good luck.

Dave

Here is a link that might be useful: Tomato Controls - Green Peach Aphid and Other Early-season Aphids

Thanks Dave, I think I've caught it early enough to use the spray bottle and pick them off. I hate having to take them out of the green house but I'll do that today. I was thinking about putting a bunch of ladybugs in the green house to see how that would work(I know where there is an abandoned house infested with Ladybugs right now). I love my limes and lemon trees as much as my tomatoes, so destroying them is not an option. Some I've had 8 years. I get about 50 limes off one tree. I do like my mojitos!! Theresa

These were on the lower leaves of my apricot tree with 2 Beefsteak and 2 Early Girls growing directly below. Apparently these were apricot aphids because they NEVER attacked the tomato plants below them,

Man, those are ugly. Aphids are somewhat selective, that is, you'll find black ones on Nasturtium yet nowhere else. A little neem oil, detergent and water will do those buggers right in. Consider easing off on nitrogen fertilizer also since a bit too much encourages aphids. Hope this helps (and makes sense too). Good Luck.