Orange Aphids on Milkweed

2017 April 12

A few years ago, Sandy planted Swamp Milkweed at a few strategic places around the house, primarily as food for Monarch Butterfly caterpillars, and the plants are mostly doing well. On September 25, 2016, Sam and Rosie told me that there were aphids all over some of them, and so I came out to have a look. And yes, the aphid infestation was pretty heavy:


The bright yellow-orange color, combined with the black legs, black antennae, and black cornicles (the two projections on their hindquarters), are extremely distinctive, to the point where I think there is only one real possibility for the species.



They are Oleander Aphids (also known as Milkweed Aphids), Aphis nerii. Their preferred hosts are oleanders and milkweeds, and probably other toxic members of the Apocynaceae family. Like a lot of other insects that eat milkweed, the bright coloration is a warning to predators that these aphids are poisonous. In addition to having the plant toxins in their bodies[1], they can also squirt poisonous fluids from their cornicles.

These aphids came over from Europe at some point, probably carried over on ornamental oleanders. The ones in North America are entirely parthenogenic, with no males. And they clearly reproduce really, really fast. There aren’t many things that eat them (lacewing larvae and lady beetles will try, but they reportedly either then don’t survive pupation, or come out with serious deformities). There are some parasitic wasps and flies that will attack them, but other than that they are probably only kept in check at all by diseases.

Luckily, the plants that they feed on aren’t agricultural crops, and in spite of their huge numbers, our milkweed plants didn’t seem particularly damaged by them. The main issue is that they transmit plant viruses. They are easy enough to see, so probably if they are a problem, the easiest thing to do is probably to either just squish them, or wash them off with insecticidal soap.

[1] It seems like just about everything that eats milkweed also co-opts the milkweed toxins for its own use, and most of them also go ahead and color themselves red, yellow, or orange as a warning that they taste awful and may be fatal to eat. The amusing thing about this is that the milkweed originally developed those toxins to keep from being eaten, and now those same chemicals are protecting some of the very things they were supposed to drive off! Sometimes things just don’t work out the way one would like them to.

2 Responses
  1. Sandy E permalink
    April 12, 2017

    Ugh! Plant ticks!

  2. April 12, 2017

    Every Spring, almost on schedule, we get aphid infestations. They’re the normal ones, so a cannister of ladybugs will annihilate them in short order.

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