Monday, February 29, 2016

The Milkweed Community Beyond Monarchs

My attempt to rescue 4 monarch caterpillars that were about to eat out their food source seemed to fail, despite my provisioning them with 6 white milkweed and 2 swamp milkweed plants from 7 Pines Native Plant Nursery.  The last - and largest - of the caterpillars curled up in a question mark on the soil surface one day and then disappeared overnight.  Eaten?  Probably.  Pupated somewhere?  Possibly.  At any rate, I have no more monarch caterpillars to watch right now.

However, I do have my 8 milkweed plants.  Making me quite sure that these plants weren't being treated with neonics, my milkweeds came pre-supplied with bright yellow aphids.  A little research on BugGuide.net informed me that these aphids are oleander aphids, Aphis neriiOleander aphids are actually native to the Mediterranean area, but they have become common around the globe, having traveled everywhere on oleander plants.  Oleander aphids are especially common on oleander and on milkweed plants, although they are known to feed on several other types of plants as well.

As I was looking for the monarch caterpillars, I noticed a fly hovering about 6" from the milkweed plants. Watching more closely, I noticed there were actually about 6 flies, and that occasionally one would dart in, look like it was depositing something, and return to hovering.

So I got my camera and tried to take a photo.  After a long time - and many attempts - I hadn't managed to get a nicely clear photo, but I had managed to get a couple shots where I was able to at least get a feel for the flies I was seeing.

Between the blurry photos, the gestalt I had, and the research I did, I think that this little fly is a species of syrphid fly, Ocyptamus fuscipennis, known both for its dark colored wings and its diet of aphids in the larval stage.  That's just my best guess, however.  It's not a verified identification.

As I was trying, again and again, to get a clear photo of one of the syrphid flies, I suddenly noticed a couple tiny, tiny wasps walking among the aphids.  As I looked through the camera lens, I watched one of the wasps curl its abdomen and seem to poke the aphids individually.  This was a little odd, because the wasp curled its abdomen relatively far away from the aphids, but I was sure that it was laying eggs on them.  Again I took photos, but again I didn't get any good shots - to get clear photos of such minuscule insects, I needed a tripod for stability and a windless day with no sway in the plant stems.

Despite my lack of good photos, I saw enough to have a good idea of what was going on.  After more research, I suspect that the small wasps were braconid wasps, which parasitize aphids by inserting an egg in an individual aphid.  The egg hatches and the larval wasp eats the aphid from the inside, killing the aphid and leaving an "aphid mummy", which is essentially the shell of the aphid with the larva, then pupa, of the wasp inside.  When the wasp emerges from its pupal stage, it cuts a hole in the aphid mummy and emerges, to repeat the cycle.  If you click on the link I've highlighted, you'll see a great photo posted on BugGuide.net of one of these wasps in egg-laying stance, ready to lay an egg on an oleander aphid.

Note:  Looking at several of my photos from this series, there are many little dots on them.  The dots were only visible when I enlarged the images and they only occurred in the middle of the milkweed plants.  I don't think it was a dirty lens (although I will certainly be cleaning it to verify).  There is also a small, beetle-like insect on the vein of the milkweed leaf in the very bottom right of the photo above, which I haven't identified.  I think it might be some sort of weevil, but that is simply another guess.

So right now, with no milkweed blooms to be had, I've already got 4 species that are relying on my milkweeds for the basis of their life cycle:  monarchs, oleander aphids, a syrphid fly, and a braconid wasp.  I've also seen examples of herbivory (monarch caterpillars and oleander aphids), predator-prey relationships (syrphid flies and aphids), and parasitism (braconid wasps and aphids).  Pretty cool for February!

11 comments:

Gardener on Sherlock Street said...

You are so aware of all the life forms in your garden. That was a very interesting post. So much going on if we just look. Glad you have the milkweed plants.

Gaia Gardener: said...

Thanks, GonSS. I suspect it's because I came to gardening from biology and birding. The animals were actually my first love.

Corner Gardener Sue said...

Cool! I remember when I used to get upset when I saw aphids on a plant. I would squirt them with a hose or try squishing them. I thought they were going to kill my plants. Now, when I see them, I expect there will be predators making use of them.

Gaia Gardener: said...

Absolutely, Sue! I love watching aphids to see what's munching on them. I'd feel better if these were the specific milkweed aphids, but at least there seems to be a phalanx of predators willing to eat the oleander aphids, too.

Corner Gardener Sue said...

LOL, I forgot that I had already read this. I was about to say something similar to what I already did.

I hope you discover new plants that are native to your new area that you and the critters enjoy.

Laura Sanders said...

I love your blog! I came across it when googling info about 'possum pellets in my bird feeder. I live in South Carolina, the Piedmont region, and my husband is a biology major-master gardener-landscaper-nurseryman. I am an amateur naturalist of the very curious sort! I thoroughly enjoyed learning about your milkweed Eco-system, as I do the same sort of observations; "What exactly is that insect? What is it doing?" I would take photos with my "real" camera, but it is old, and the lens motor is broken, so I do what I can with my LG phone these days. Keep blogging!

Gaia Gardener: said...

Sue, I thought I was the only one who did duplicate posts! LOL! Isn't it cool about how predators keep so many plant eating bugs under control, when you let them?!

I've got several things blooming and need to make a couple more posts, but finding the time gets dicey these days. Should be squeezing it in soon, though.

Gaia Gardener: said...

Laura, you made my day this morning! Thank you! Any chance you are going to take up blogging? It sounds like you and your husband make some interesting observations and discoveries, too. Cynthia

Corner Gardener Sue said...

So, you've done that before, too? I think this may not have been my first time, either. Thank you for your words of comfort on my post about our dog.

Cam @ArcadiaTrails said...

I have a lot of milkweed in my butterfly garden (we get lots of caterpillars in the spring and fall), and the aphid infestation gets so bad it stops the plants from flowering and bearing seeds. :(

Gaia Gardener: said...

Cam, I wonder why you're not getting predators coming in to eat the aphids? An easy strategy to use, in the interim, is to wash the aphids off with a strong spray of water - they are not very mobile and generally can't climb back up on the plant. Of course, new ones will colonize, but the plant will have a breather in the meantime. Watch out for predators before you try to get rid of the aphids - one year I found a lacewing egg AFTER I had washed the aphids off, and I felt guilty for starving the poor emerging larva.