365 Urban Species. #310: Oleander Aphid

[urbpan]

Photos by urbpan. Location: common milkweed plant on the shore of Leverett Pond, Boston.

Urban species #310: Oleander aphid Aphis nerii

There are a few species of aphids which are generalists, feeding on a range of different plants. Most, however, drink the juices of a small subset of similar plants, such as the lettuce aphid (which feeds primarily on lettuce, but may also feed on artichoke and petunias) and the oleander aphid. The oleander aphid is thought to have originated in the Mediterranean, but has now spread worldwide, having been exported along with its host plant. Of course, oleander is a subtropical plant, so in order for the oleander aphid to spread to northern regions, it needed to find an alternate host. It has found that milkweed plants serve quite nicely. In places where oldeander will not grow, this insect may be called "milkweed aphid."

One thing that oleander and milkweeds have in common is that they are both quite toxic, bearing chemicals called cardenolides. Oleander aphids are able to take this poison from their host plant and store it. When a predator attacks, cardenolides are emitted from "cornicles," which are appendages on the top of the insect's abdomen. Usually this repels the predator, but if not, the poison does its dirty work. In an aphid predator such as a lacewing or ladybug, the poison can render the insect sterile, or interfere with wing development. The aphid presents a fair warning in its coloration: bright yellow-orange with contrasting black appendages. This caution sign combination works for all kinds of bees as well as the monarch butterfly (another milkweed feeder that uses cadenolides in defense).

Oleander aphids are thought to be all female, reproducing through parthenogenesis. Generation of wingless daughters and granddaughters are born and spread until they reach a point when the plant can support no more of them. Then a generation of winged aphids is born and they fly to new host plants. Like many other aphids, oleander aphids produce honeydew as excrement, but their honeydew contains the same poison they use to protect themselves. Some species of aphid are protected ("tended") by ants, who consume the honeydew. The giant milkweed we examined in Antigua had both aphids and ants; are there certain ants that can cope with the poison? Or since worker ants are both wingless and sterile, is the poison's effect moot? I hope this question is explored in the entomological literature, but I could not find it. It does seem that while the aphid causes little harm to the host plant, the uneaten honeydew accumulates and grows a fungus called "sooty mold," which is considered unsightly.

Oleander is a widely planted ornamental in cities throughout the tropical and subtropical world. Milkweeds such as butterflyweed are likewise planted, in temperate cities and suburbs. And common milkweed and giant milkweed survive in roadsides, parks, and vacant lots everywhere. Wherever these plants are, they are accompanied by their aphids.




Oleander aphids are visible on the stem of this fruiting milkweed plant.


On a milkweed pod, a few winged aphids get ready to move on.

See the entry for giant milkweed for cottonmanifesto's oleander aphid photo. It's better than mine, of course.

Comments

[phlogiston-5.livejournal.com]

I think I have seen ants tending these guys. I'll see if I can find anything interesting in a lit search.

Also, an aphid enthusiast friend of mine informed me that the name "cornicles" has been changed to "siphunculi". Because scientists like funny names.

[urbpan.livejournal.com]

Excellent! I'm not sure if "cornicle" or "siphunculi" is sillier. I guess siphunculi (plural of siphunculus!) is pretty silly. If it's the latest, I'll go edit my post. Thanks!

singular

[urbpan.livejournal.com]

"Siphuncule," apparently.

Paedogenesis

[(Anonymous)]

So not only can aphids reproduce through parthenogenesis they also reproduce through paedogenesis. So not only do they not need male aphids they can also be born pregnant! Paedogenesis is defined as "parthenogenetic reproduction by larvae structurally unable to copulate." The aphid nymphs are developing in cells in the mother's body while she is still unborn. However the aphids can not give birth to these nymphs until they are mature (which only takes about 7 days).

Insectophile :)

[artemii.livejournal.com]

yeah, i've always thought it was really cool that many (all?) species of parthenogenic aphids can be born pregnant.

here in new england, i've mostly found these aphids on the large milkweed plants, particularly on common milkweed and purple milkweed. i almost always find ants tending them.

[wirrrn.livejournal.com]

Hey,

As far as I know, Oleander Aphids are given a wide berth gby the various ant species that Milk other aphids. They know that the Oleander Aphids pack a powerful hangover *g*.

Ladybug Beetles and Lacewings avoid them, but fortunately, parasitic wasps (eg Braconidae) are not so encumbered, and still zap the Oleander Aphids with their ovipositored larvae. The Wasp Larvae seem to avoid eating the gut contents!!

Aphid mummies

[(Anonymous)]

Has anyone seen any aphid mummies around here? I love the way the wasps make little trapdoors upon exiting their host. In California we had at least two specieis of wasps that parasitized aphids one which left a black mummy and one that left a brown mummy.

Insectophile

milkweed aphid

[(Anonymous)]

In my experience milkweed aphids do result in plant injury. Usually they are most abundant on the young or top of the stems, which eventually wilt and dessicate due to the heavy feeding. If a plant is heavily infested, the entire plant will begin dropping leaves. By this point, the aphids have moved on to another plant. I have had serious infestations on commercial cut flower crops of milkweed and foxglove.

milkweed aphid

[(Anonymous)]

Oh, I forgot. Apparently hover flies (flower flies) larvae will eat this aphid -- hooray! I will be looking for this next year.

ladybeetles eat milkweed aphids

[(Anonymous)]

Actually, I have been very successful controlling milkweed aphids by releasing ladybeetles purchased for this specific purpose. In fact, this experience was so amazing-- totally gone in 3 days although I saw few ladybeetles actually on the infested crop -- that I started using more biocontrol insects. Over 150 plants were seriously infested prior to release of the ladybeetles.

Re: ladybeetles eat milkweed aphids

[urbpan.livejournal.com]

Thanks for the information!