Golden aphids

[PatP]

Despite what I read regarding there being no serious pests for Butterfly weed, mine last year was practically devoured by what looked like golden aphids...and they're back this year! I hose them off and they come right back. No pesticides, as that would kill the caterpillars, and the ladybugs seem overwhelmed. Any ideas??

[IntrepidMeredith]

Try insecticidal soap. It only affects soft-bodied insects like aphids (and, yeah, caterpillars), and shouldn't be any problem for the ladybugs. As for the caterpillars, I believe the insecticidal soap has to coat the insect in order to kill it, so if you try spray only areas with aphids and skip any leaves with the caterpillars, the caterpillars should be OK.

My understanding is that the insecticidal soap clogs the pores that the insects use to breathe, thus suffocating them. If the bugs eat the stuff, it doesn't do anything. You may want to double check this last bit, but I'm pretty sure it's correct.

[KimmSr]

First, the aphids you knocked off did not "come back". What you saw was another generation of aphids move in to replace those you knocked off the plants. Since aphids can reproduce almost as soon as they are born, they are born live not by eggs as many other insects are, you can easily have 5 or more generations on a plant before you are even aware they are there. Just wash those you see off the plants when you see them as often as you see them and, eventually, they will be gone.
Insecticidal soaps do not clog the breathing pores of the insects but it will disolve the exoskeleton of the insect, which means insecticidal soaps can adversly affect many beneficial insects such as the Lady Beetles. Due care in use of insecticidal soaps, as any other pesticide, is necessary.