Literature Review: Milkweed Insects

by Carl Strang

This week’s peek at the scientific literature is a recent study published in the journal Science. My source is an article about that study in the science review site ScienceDaily.

Y. Zhen, M. L. Aardema, E. M. Medina, M. Schumer, P. Andolfatto. Parallel Molecular Evolution in an Herbivore Community. Science, 2012; 337 (6102): 1634 DOI: 10.1126/science.1226630

They examined genes of insects from several orders that feed on milkweed and dogbane plants. Though the insects (butterflies, moths, beetles, true bugs, aphids) are well separated from one another in their taxonomy and evolutionary history, they share the basic genes regulating cellular exchange of sodium and potassium, the proteins for which are affected by the plants’ poisons. A common pattern was gene duplication, with one copy available to mutate into a resistant form that allowed normal exchange of those ions within gut cells. The same gene was involved in all those diverse species, indicating the course of evolution was somewhat predictable.

Here is a gallery of local insects which eat milkweed and dogbane leaves, illustrating the diversity.

Monarch

Large milkweed bug

Red milkweed beetle

Milkweed tussock moth caterpillar

Milkweed leaf beetle

Dogbane beetle

Note how common orange appears among the milkweed insects’ colors. Is there a common genetic factor there as well?

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Bioblitz Incidentals

by Carl Strang

While my main focus at the Kankakee Sands bioblitz was on observing singing insects, I also was noting other species along the way, and was interested in others’ observations of singing insects. Someone in the Purdue entomology group collected a female bush katydid, for example.

The ovipositor marks it as female, the wing proportions and head shape place it among the bush katydids (genus Scudderia).

Female bush katydids are tricky, but I’m pretty confident that this is a Texas bush katydid. The sharp bend in the ovipositor, especially the inward or upper edge, narrows it down to a very few species. A broad-winged bush katydid would have broader wings, and a fork-tailed bush katydid would have a reddish-brown rather than green ovipositor. The colors and shapes of other structures around the ovipositor, and the shape of the ovipositor itself, match those of the Texas bush katydid, which is a common species of prairies like the one where this insect was collected. I didn’t hear any singing, but in DuPage County these tend to start up later in the season.

I saw a number of little yellow butterflies that had the markings of sulphurs but were unfamiliar to me.

The little sulphur is a species associated with sandy soils, and so unlikely to turn up in my familiar DuPage County haunts.

A milkweed leaf beetle turned up in a sweep sample in one of the prairie areas.

Like so many other milkweed feeders, this species has colors of black and orange.

Alyssa noted that I had picked up a hitchhiker at one point.

This proved to be Henry’s marsh moth, a noctuid of wetlands with a broad larval diet.

One of our nets caught an impressive jumping spider.

It was a big one, marked by a white stripe across the abdomen.

Finally, I photographed a grasshopper nymph that I thought might belong to a stridulating species, but I think it is in the wrong group.

I heard a grasshopper stridulating, but never saw it, and was only guessing here.

Grasshoppers are a group I usually will need to collect for identification.

The American Snout, and More

by Carl Strang

One of my favorite animal names is “American snout.” It calls forth the image of some disembodied nose floating in space. In fact it’s a reference to a butterfly with a long forward extension of its head.

This butterfly was the first of its kind I have observed at Mayslake Forest Preserve. It is more common south of us. In references you may find its species name as carinenta or bachmanii; the genus is Libytheana, and there is only one North American species.

Another preserve first was this brightly colored beetle.

The milkweed leaf beetle, like so many consumers of milkweed, has bright orange colors. These warn potential predators of the possibility of poisons the insect may have sequestered from its diet.

I saw a couple bluets that had the relatively large size and the color pattern of familiar bluets.

The males had this violet coloration, though; my guess is that they had recently emerged as adults and would be changing colors soon.

I have been seeing more Virginia ctenucha moths than usual this year, at Mayslake and elsewhere.

That’s the way it is with some insects, having occasional years with higher numbers.

Of course, a major goal of all these adult insects is to find a mate and produce eggs.

For this pair of least skippers, it’s so far, so good.

On Friday I finally saw the first Peck’s skipper of the year.

The pattern of light spots beneath the hindwing is distinctive for this species.

It’s been a good year for insects, so far.

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