They're aphids. Lots of them. Sevin doesn't work on aphids. Just squish or power-hose them off.

You have learned that Sevin kills any insect, good, bad, or indifferent and is not something that should be used in any garden. What you have there is Aphids and they can easily be controlled with a sharp water stream that knocks them off the plant (a spray bottle is all that is needed for this, your water hose will most likely have too much pressure and could destroy your plants) and once knocked off the wee buggers will starve to death before they figure out where they came from and how to get back there. More Aphids will appear, not because as some people that know not much about Aphids will tell you because they return, because Aphids start to bear live young almost as soon as they are born themselves and these next generations are what you see. You could easily have 5 or more generations of Aphids on your plants (with many more coming along) before you even know they are there.