(see guide) and we have five so far. So we are definitely not all-inclusive. But we have been calling all these yellow aphids on Milkweed Aphis nerii, for what that's worth. A Google of aphid and milkweed also shows up something called Aphis lutescens or milkweed aphid, although in some images that appears to be more orange than yellow- and some sites call Aphis nerii Milkweed Aphid, too.