Monday, August 07, 2017

Syrphid Fly Scouting Place to Lay Eggs

In my recent post on aphids and their predators, I shared photos of two types of syrphid fly larvae that I am seeing.  A few days later I was lucky enough to get this photograph of an adult syrphid fly, looking for a place to lay eggs on my milkweed.

If you click on the photo, you can see the details that are not apparent in the smaller image imbedded in the text here.  Note the aphids at the base of the flower cluster?  There aren't a lot and I didn't see the female syrphid fly lay any eggs, so she may have decided that she needed to look for more populous aphid clusters.

Going by the Latin name of Ocyptamus fuscipennis, there is no common name for this syrphid fly.  I am pretty sure that this is the adult form of the "gray slug" syrphid fly larva that I see munching on oleander aphids. 

Here is a closeup of this individual....

(Note:  I have not raised an individual from larva to adult to know for sure, but this is both the most common syrphid fly that I see laying eggs on the milkweed and the most common adult syrphid fly larvae that I see.  Others have raised this species from larva to adult, and the larva does look very similar to this.)

What predators are you seeing munching on YOUR aphids?!

Friday, August 04, 2017

Sand Wasp Grows Entirely On True Bugs

When I first saw this good-sized wasp, I thought it looked a lot like a cicada killer.  I couldn't get very close to it to get decent photographs, but I was able to get good enough images that I knew it wasn't my old friend from Kansas.

Tonight, after I cropped the photos to more closely see the insect I had "captured", I tabbed over to and started looking around.  After a while, I thought I had probably figured out the identification...but the eye color was wrong and the markings on the thorax were not quite right either.  So, I posted the photos and asked for help.

Meanwhile, I continued searching through BugGuide, looking for a better match to my mystery wasp.  As I was checking out a particular species, a sand wasp that is known only as Bicyrtes quadrifasciatus, I saw a couple photos that looked remarkably familiar.  When I checked my email, I was stunned.  My original identification had, indeed, been wrong;  the species I was looking at now was the correct species; and - most surprising of all - one of the contributing editors at BugGuide had already made the identification and moved my photos to the correct spot!   Those WERE the photos I had just uploaded a few minutes before.

BugGuide for the win!

So why do I try so hard to identify "my" insects to the correct species?  This wasp is a good example.  By learning the identity of this wasp, peacefully feeding at a flower, I learned that I host a species of solitary wasp that raises its young completely on true bugs, on insects like stink bugs and assassin bugs and maybe even milkweed bugs.

Seriously.  This species of wasp finds enough true bugs in the general area of my yard to raise its entire brood of young for the year on the bugs that it finds and paralyzes, drags back to its nest, and lays eggs on.  Isn't that incredible?  Talk about natural pest control.  Talk about the "balance of nature".

To top it all off, as an adult, this wasp acts as a pollinator on flowers in my garden.  Before I started learning about the specific identities of the insects in my garden, I had no idea that wasps were such extraordinary predators or that adult wasps generally just ate pollen and nectar.  Based on a childhood experience, I was actually quite scared of them.  Now wasps fascinate me, and the more I learn, the more fascinated I become.

I am continually stunned by the complex interactions occurring all around me - interactions that I simply don't see or even know to look for.  The natural world is truly a marvelous, intricate web of life whose structure we would be wise to cherish, rather than destroy.

Thursday, August 03, 2017

Predators and Parasites on Oleander (Milkweed) Aphids

My milkweeds are hopping these days.  Sadly, I've only seen one monarch caterpillar, but I am still fascinated by all the insect life that I am seeing.  Most of my observations have been on tropical milkweed (Asclepias curassavica) simply because I have several big, healthy plants in pots on my back patio and they are easy to check on and photograph, but I'm fairly certain that what I'm seeing isn't unusual for other milkweed species.

The orange-yellow oleander aphids (Aphis nerii) are common on these plants.  A week ago, when many of these photos were taken, the aphids covered about 2-3" of the top of every shoot.  This week their numbers are much reduced, with just a few hardy individuals remaining where hundreds dined last week.  This is at least the second rise and fall of aphid numbers on my plants this summer.  I'm sure they will go through at least one more population cycle up and down before frost comes this autumn.

So what's keeping the aphid populations from exploding out of control?  If you look closely at the photo above, you can begin to see the answer.  Specifically, here are some of the candidates I've been seeing....

Each milkweed shoot with its covering of yellow aphids near the tip seems to also have at least one or more of these blobs of gray and white protoplasm which, I am pretty sure, are actually syrphid fly larvae.  Although the blobs are stationary when I usually see them, I have occasionally seen one "hightailing" it from one area to another.  Looking on, this looks like the larva of the syrphid fly, Ocyptamus fuscipennis.  I have certainly noticed syrphid flies that look like these adults hovering around the aphid clusters.  There is no common name for this little fly that I know of, but the BugGuide link will allow you to see what the adult looks like, so that you can notice if your milkweed aphids are attracting attention from this species, too.

Less common, but still easy to find, are these little bumpy caterpillar-like animals that are also, I believe, syrphid fly larvae.  I've not been able to figure out which species or even genus these guys belong to, but I do find it fascinating that two different species of syrphid flies are munching on my oleander aphids!  The only way to really tell for certain would be to raise up some of these larvae to adulthood, which sounds like a fun project when the boys get a little older.

If you ever see a piece of trash seeming to move on your plant, look a little more closely....

You may be seeing a green lacewing larva, which hides under a pile of debris that includes its castoff skins from earlier molts. 

If you look closely in the photo above, you can easily see the yellow oleander aphid being the actual lacewing larva at the bottom of the pile of debris.  Lacewings are fierce aphid predators as both larvae and adults.

Not uncommonly among my aphid populations, I will see a dark brown aphid that doesn't move.  This is an aphid mummy.  Tiny parasitic wasps lay an egg in an individual aphid and the developing wasp larva eats out the insides of the aphid, leaving the aphid a literal shell of itself.  Only one baby wasp per aphid, but each female wasp can then go on to lay eggs in many aphids, so aphid mummies are welcome sights on my milkweed plants.

There are other more generalist predators that I'm seeing around my milkweeds, too, which may or may not be preying on the aphids.

I often see tiny, longlegged flies, for example, flying around and landing on milkweed leaves for short periods of time.  Longlegged flies (Family Dolichopodidae) are iridescent green or brown and are known to be predators in both the larval and adult forms.  Although I have never seen one pay attention to, let alone eat, an aphid, I can still hope.  They've got to be eating something!

Clad in the red-orange and black colors of the classic milkweed insect, milkweed assassin bugs (Zelus longipes) are another generalist predator that I see these days, both on milkweeds and on other plants around the yard.  I see the milkweed assassin bugs hunting up and down the plants, sometimes hanging out in the flowers, but just as commonly walking up and down the stems or inspecting both sides of each leaf.  Their eyesight is superb and it can be hard to sneak up on one to take its picture.  At first it will simply duck to the other side of a stem or leaf or flower cluster, but if you persist, it will readily fly away.

The final predator I've been consistently seeing around my milkweeds in recent weeks is a damselfly.  Again, I don't know if this dainty creature is eating winged aphids or not, but I doubt it would turn one down.

So, as you look at the aphids on your milkweeds in horror and dismay, look a little closer - there's a good chance you'll see some other, interesting insects drawn in to the feast that they represent in the animal world!