FWIW, I don't spray the aphids on my milkweed because they attract ladybugs & lacewings & I often see the larvae of those beneficials among those aphids, not to mention teeny tiny monarch caterpillars.

Carolb_w: Don't the aphids destroy your new growth and blossoms? It appears that my aphids are intent on doing just that.

I haven't seen much damage - perhaps because predator bugs eat the aphids before they do much damage. OTOH, milkweed bugs really mess up the plants...

My milkweeds usually have a lot of aphids. They stay that way for awhile and next thing you know, the lady bugs appear to snack on the aphids. I don't really care if there are aphids on my milkweed. They don't really do all that much damage and the caterpillars come strip off the leaves and then the plants or should I say sticks lol, sit there for awhile looking pathetic and half dead until they grow new leaves and the whole thing starts over again. Somehow they manage to reseed themselves all over the yard and we have lots of Monarchs now. If the milkweeds completely disappear I will just get some new seeds and replant them.

Ladybugs won't come unless there is a sufficient population of aphids to attract them. One of the reasons for growing milkweed, aside from butterflies, is to bring in the ladybugs and help keep the aphids off the roses and other plants. Another plant that attracts heaps upon heaps of aphids is called butterfly weed. Hmmm, I'm sensing a theme. I wonder if butterflies and aphids are related?

Aphids seem to be a problem on tropical milkweeds but then they are destroyed by parasitic hoverflies (or something like that.. they're purpleish and thin? but don't seem to be small wasps). This is usually what happens with me: Oh no they are everywhere!! (two days later) most are gone and replaced with brown husks.. and then months can go by before I see another one. I saw one aphid today after 3 months of no oleander aphids.

I have NEVER found spraying necessary. I have hand killed before but it has not been necessary except a week or so after planting a new plant that the flies hadn't helped yet.

Milkweed bugs on the other hand... I have had to control on and off manually. I have yet to find a predator for them.

@Bea: I read what caused some to be more prone to aphids than others and I'm so annoyed that I forgot what it was! It had something to do with the stem thickness I think.