I was so excited to find aphids on some of my goldenrod (Solidago missouriensis)- my garden is all coming together.
Every gardener knows a thing or two about aphids. They are usually green or dark-colored and are one of the most common garden pests. They have sucking mouth parts, and their mortal enemy is the ladybird beetle (Coccinella spp.), aka ladybug.
Less known is that most native aphids are host-specific, that is, they only feed on one or a group of closely related plant species. The neat thing about the aphids in my photos, Uroleucon nigrotuberculatum, is that they are red (so they are easy to spot on a goldenrod stem). This is a relatively rare aphid that feeds on tall goldenrod species.
In the literature, this species is well studied because it demonstrates some important theories of predator-prey relationships. As the patch size of the host plant gets bigger, the rate of predation on the aphids goes up. I guess in our yard now we have patchy goldenrod, and thus a great home for these aphids and the native ladybird beetles they attract.
On garden plants the wingless females are the first ones that are visible, but as their population grows or as pressure from predators increases, individuals are induced to produce wings and fly off to colonize new areas.
Delighted with these aphids appearing on a few goldenrod stems, I looked them up on the Internet to find other gardeners which which to share my delight. There must be many already delighted gardeners out there, I thought, with the proliferation of wildlife gardening, pollinator gardens, green gardening, and so on. However... I was socked at what I found. Cue the scary movie music and read on.
There were, indeed, a bunch of websites with information about goldenrod aphids.... (wait for it)... and how to kill them! Even the gentle methods destroying them and their kin with earth-friendly (not aphid-friendly) biodegradable, free range, organic, etc... insecticidal soaps.
Here is a typical thread:
Question- What are these ugly red bugs?
Answer- Aphids. You had better kill them before they kill you and your family
Question- I knew it, they looked gross. I will kill them, but how? How can I kill them without using chemicals? I am a green, earth-friendly, holistic gardener.
Answer: Use a hose and spray them off
Question: Will that kill them? I don’t want them out there, doing damage to other plants, I want them dead, after all I care about the environment and all the creatures in my garden.
Answer: Use organic soaps, rub the soap into their soft bodies, and even squish them with your hands. Don’t let any get out of your sight, they can clone themselves and they may have already laid eggs, so plan of several treatments.
You should not just go around killing things. Try to understand the biology and ecology of animals and pests, first. These aphids, like many other aphids on plants in your yard, will not affect any other plants other than the ones they are feeding on, in this case goldenrods, and their effect on goldenrod is negligible. Furthermore, since they attract ladybird beetles and their larvae, the aphids are probably a very beneficial pest in your garden.
Speaking of ladybird beetles, commercial ladybird beetles sold as bio-controls for aphids is a booming business. Using for aphids and other pests is often thought of as a better, safer alternative to other control methods. However, as a result of their popularity, several of the common ladybird beetle species in North America are actually invasive species from Europe or Asia. These were introduced to this country as bio-controls, by well- intentioned gardeners. Some species of non native ladybird beetles are now the most common ones in the mid-west and elsewhere in the US.
Let me close by saying that I do squish aphids on my vegetable plants, but not because I'm afraid of them going to my goldenrods.