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?

July Insect Phenology

by Carl Strang

First observation dates for insect species at Mayslake Forest Preserve in July 2011 were not too different from 2009 and 2010. The median difference in dates placed 2011 ahead of 2009 by 3 days (range 17 days earlier to 16 later, sample of 13 species). This year’s July appearances were a median 7 days later than in 2010 (range 30 days earlier to 80 days later, sample size 15 species).

The red milkweed beetle was representative of these results, with a first observation date in 2011 that was 3 days earlier than in 2009, 6 days later than in 2010.

Dropping the 80-day-later outlier, which probably represents my missing a generation earlier in the season, shifts the median difference between 2010 and 2011 to 5.5 days later, not a very big change.

More Mayslake Lepidoptera (and others)

by Carl Strang

A couple days ago I updated the dragonflies and damselflies I have been finding at Mayslake Forest Preserve in my first year there. Today I’ll continue with newly sighted butterflies and a moth. These include black swallowtails, both female

black swallowtail female b

and male.

Black swallowtail male b

I have not seen larvae, but there are plenty of Queen Anne’s lace and other members of the family Umbelliferae that are potential food plants. When I saw the following hairstreak, I made sure to get photos.

Banded hairstreak b

This proves to be a banded hairstreak. A year ago I was alerted by Forest Preserve District invertebrate biologist Tom Velat to watch for southern or oak hairstreaks. That alert was prompted by the following photo I took of that species at Fullersburg, which I failed to identify correctly.

Southern (oak) hairstreak b

The hairstreaks require a close study of patterns in the lines of dots beneath both wings, and the arrangement of colors in the corner of the hindwing. I have one moth to share this time, the reversed haploa.

Haploa reversa Reversed haploa b

Haploa is a genus of tiger moths. I’ll close with three insects of milkweeds. The first is a familiar butterfly, the monarch, here visiting a purple coneflower in Mayslake’s Historic Garden.

Monarch Echinacea b

Monarch caterpillars feed on the leaves of milkweeds, in the process sequestering defensive poisons which then protect the specialist insect from its own consumers. Other insects have solved the milkweeds’ chemical challenge, and gone on to advertise their own poisonous status with bright colors. Two species in this category which recently have appeared at Mayslake are the red milkweed beetle

Red milkweed beetle b

and the large milkweed bug.

Large milkweed bug b

I’m sure I have barely scratched the surface of Mayslake’s Lepidoptera.

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