Many years ago I found aphids infesting a little milkweed plant I'd purchased but had yet to plant. I didn't want to spray chemicals, but I was concerned that the little plant wouldn't make it - and I was concerned that the aphids would spread to all the other plants in my garden. Feeling very noble and "green", I hooked up a strong sprayer to the hose and simply, carefully, sprayed all those little yellow aphids off the plant. Ah, I'd saved it!
Except that when I got to looking at the milkweed plant after I'd washed the aphids off, I noticed a lacewing egg on its willowy stalk. I'd washed off all the food that the lacewing mother had planned for her offspring to eat and thus I'd managed to kill the beneficial-predator-to-be.
Note: The photo above is of a lacewing egg, but on a tree leaf, rather than on a milkweed. The egg on the tip of the stalk is diagnostic, as far as I know, of a lacewing egg. Sadly, I don't appear to have photographed my little milkweed/aphid/hose experiment, but I thought you might be interested in what a lacewing egg looks like.
Back to the story..... Feeling a little sick at heart after spraying off the aphids and finding the lacewing egg, I took to the web to do some research. WHY didn't I do that research BEFORE I reached for the hose sprayer?
It turns out that most aphids are pretty species specific regarding their host plants. The little yellow aphids with black legs on milkweed are oleander aphids (Aphis nerii) and are found primarily on milkweeds and oleanders. These little aphids were never going to be a problem on my asters or Echinacea or garden vegetables.
Interestingly, oleander aphids are not native to North America. They were brought here along with oleanders, which are also not native. Luckily, unlike with many other non-native insects like Japanese beetles, there ARE predators and parasites that will help keep oleander aphid populations under control.
In this photo, for example, it's easy to see both the yellow oleander aphids and the aphid-eating syrphid fly larvae on the tropical milkweed. The syrphid fly larvae are some of the predators on oleander aphids.
Fast forward to recent days.
Evidently, with so many more people planting milkweed for monarchs these days, a lot of folks are suddenly noticing oleander aphids on their milkweeds. Questions abound about how to kill these aphids without jeopardizing the monarch caterpillars.
In my experience, thanks to the work of predatory insects, the populations of oleander aphids on milkweeds will cycle up and down, but will almost never hurt the plant. Since I think chemical alternatives do far more harm than any possible good, I freely share my experiences whenever it seems appropriate.
Now I'm curious to see if I can tell what predators will show up to help thin the ranks of the young large milkweed bugs. How could anyone ever be bored in a garden?!