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?

Late Season Insects at Mayslake

by Carl Strang

A couple days ago I put a finish on the floral season at Mayslake Forest Preserve. Today I’ll shake a few late insect photos out of the camera. We’ll start with some Odonata.

Green darner b

At Mayslake as elsewhere, hundreds of common green darners paused in their migration to hunt above the prairies and meadows. Migrating south is thought to be worthwhile for them and other large, strong dragonflies as they can extend their breeding season and spread their genes over a larger area. The various saddlebags species also migrate. Here is a UFO shot of a Carolina saddlebags that graced the mansion lawn area one day.

Carolina saddlebags 2b

A darner that shows up in a lot of places late in the summer is the shadow darner.

Shadow darner 3b

That vertical perching posture is typical. Common milkweeds have been hosting a late-season caterpillar, the milkweed tussock caterpillar.

Milkweed tussock moth caterpillar b

They are larvae of a tiger moth. I’ll close with a predator. This Chinese mantis assumed a cheerleading pose.

Chinese mantis 1b

Then, it began to groom its hunting apparatus.

Chinese mantis 2b

Earlier I showed an egg mass, which is how the species overwinters. Soon all the insects will be going into their various dormant forms to survive the long, cold, dry months of winter.

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