Aphids

Your pests are likely aphids, although we can’t see them clearly. If they fly, they are probably whiteflies. The black sticky stuff is sooty mold. Aphids and other small, piercing and sucking insects like scale or mealybugs, often require repeated sprayings to kill all stages of the insects. Try spraying every 3-4 days for two weeks, then see if insects recur. Insecticidal soap and neem are good organic options as direct contact sprays. Both are rated for edible plants. You can also spray with a strong stream of water. They’re not hard to defeat, but it may take a couple of battles before you win the war. You’ll also have to make sure there are no ants in the trees. Here’s some more info:http://www.ipm.ucdavis.edu/PMG/GARDEN/FRUIT/citrus.html