Aphids

You’ll want to get control of these pretty quickly. They don’t usually kill plants, but they will excrete lots of plant sap called “honeydew”; this attracts ants and provides the perfect environment for the growth of sooty mold. This mold doesn’t actually infect the plant but it will reduce the amount of sunlight that reaches the leaf cells and reduce photosynthesis, which of course will affect the plants ability to produce new leaves and fruits. We’ve included a link about Aphids, but at this stage you’ll probably want to use a pesticidal soap; they’re available at your local garden center. You’ll need to follow the label directions and make sure the plants are well watered before you spray them. You’ll also need to follow-up, most likely, with more sprays, but again be sure to follow the label directions for best results.
http://www.ipm.ucdavis.edu/QT/aphidscard.html
Scroll down to the bottom of this page and click on the Read More About Aphids link for more detailed info.