Pests on tomato leaves
I believe the first photo shows flea beetles and the second aphids. The flea beetles generally are not a serious problem on tomatoes. The aphids might reduce the vigor of the plants, but can be dealt with by simply washing them off with water or using insecticidal soap.
I disagree with the insect identifications. The insects in both pictures are whiteflies. The darkly colored ones are nymphs that have been attacked by parasitoid wasps.
Thank you for replying to my question. I agree with your identification. I've been aware that I have a white fly problem; however, I was surprised by all the little black specks that suddenly appeared after I was away for 4 days. After reading your reply, I've read online that the tiny Encarsia wasp had actually been brought into greenhouses to control whitefly population. So my next question: Is there anything I need to do about this situation or should I just be thanking the little wasps for helping to control the whiteflies?
It is very difficult to control the whiteflies with pesticide treatments without harming the parasitoids. I suggest keeping a close eye on the relative numbers of live and parasitized whiteflies. If the the percentage of whiteflies with parasitoids inside them over time I would wait longer; if healthy whiteflies start to increase in proportion, consider a pesticide treatment. Of course, if the condition of the foliage is declining fast, you may have to spray even if there are lots of parasitoids.