There are red aphids in the genus Uroleucon that attack false sunflower. For much of the year aphids don't lay eggs but give birth to live young, which is how they manage to reproduce so quickly. There's a picture of one of these red aphids giving birth on Bugguide here:
http://bugguide.net/node/view/...
Uroleucon apparently primarily affect plants in the Asteraceae, so if that's what they are then they aren't likely to spread to other plants not in that family. You won't find a species of aphid attacking all plants. Sevin often doesn't work well for aphids and in fact may increase the problem with them by reducing beneficial insects.
Are you certain it is the aphids that are killing the plants - are the plants that small that they can't handle it?
