The rush milkweeds are lovely this week.
They are flowering.
Here is what the plants looked like on March 19, a month ago.
The stems were covered with oleander aphids.
On April 17, 2018 you can't find a single aphid.
What did I do to get such clean plants?
Nothing. Let nature take its course.
Insects like aphids have boom and bust cycles.
Back on March 19, these aphids were under attack. They were turning into mummies, which means they were parasitized by tiny wasps.
The aphids were also being eaten by flower fly larvae, aphid flies, and a few other insects.
Inside, the plant might have been mounting a defense, too. Plants can increase their chemical fortifications in response to insects feeding on them. Milkweeds are well defended because they contain cardenolide toxins, as well as a milky latex. The aphids can overcome the plants toxins better than most insects, but eventually it is probably has a toll and the aphids are weakened.
Although they are gone right now, the oleander aphids are likely to be back again. It is a natural cycle.
Did you guess the identities of the milkweed insects from last week? Let's check.
- The yellow-orange insects on the stem are aphids. More specifically, they are the oleander aphid, Aphis nerii. Hint: Aphids are the ones with two "tailpipes" or cornicles on the back.
2. The red and black one insect might be hard to tell from this angle, but it is a true bug. A little one with two white dots in the wing is a small milkweed bug, Lygaeus kalmii.
3. This one was tough because the photograph isn't very close. It is an assassin bug, Zelus renardii. It is probably waiting for a bee or fly to capture.
4. I think everyone recognized the praying mantis. In this case, it is the Mediterranean mantis, Iris oratoria. (See previous post).
5. This one is tricky. Cirrelda correctly recognized it is a lady beetle.
6. The pale green oval at the end of the hairlike stalk is the egg of a lacewing. (Life cycle in previous post).
7. The cute striped caterpillar will turn into a monarch butterfly.
At this time of year, the butterfly will probably migrate farther north to lay its eggs on another milkweed plant.
We're glad it stopped by.
We have talked about aphid mummies before. They are the hardened shells formed when the aphids are parasitized by tiny wasps.
This week the oleander aphids, Aphis nerii, have a high percentage of mummies. In fact, it was hard to find healthy bright yellow aphids. The mummies are all the beige to dark brown forms.
In this photograph there's a winged aphid that is mummified (the only live aphid is right behind it).
If you look closely, you can see the dark round hole in the back to the aphid's abdomen where the adult wasp emerged.
Parasitic wasps are one reason aphids may disappear from plants so quickly.