Return to Pachyschelus

by Carl Strang

Last winter I described a leaf-eating beetle, Pachyschelus purpureus, which has a diet contrary to the usual rules governing leaf-eating insects. My past observations have been that, instead of eating a variety of tree leaves, or focusing on a group of herbaceous plants with similar defensive chemistries, this beetle scrapes holes in the surfaces of both wild geranium and bitternut hickory leaves at Meacham Grove Forest Preserve.

Geranium beetle on leaf b

I was interested, then, to read in Missouri entomologist Ted C. MacRae’s blog, Beetles in the Bush, that he has studied beetles in genus Pachyschelus. Through e-mail correspondence I have learned from him that purpureus larvae are leaf miners, known to develop in geranium leaves. Ted encouraged me to continue observing these beetles, to see if indeed there is a particular connection between them and bitternut hickory.

Pachyschelus hickory 2b

The above photo I took in the late summer. I found only a few scattered Pachyschelus this year, and though they were resting only on geranium and bitternut hickory leaves, none were feeding. Thanks to Ted I now know that purpureus adults are known to feed on a variety of tree leaves. My observations simply may be of beetles taking a bedtime snack before finding winter shelter. In the spring they will emerge and lay eggs on larval host leaves. I want to continue studying this beetle at Meacham Grove, however. I want to learn to recognize their mines. Our expectation is that these will be limited to geraniums, but if I were to find them in bitternut hickory as well, that would open the possibility that incipient sibling species, separating to specialize on two separate larval hosts, may be evolving.

Incidentally, take another look at that last photo. While searching for the beetles this year I was struck by the white spots on the elytra, how they resemble eyes (complete with antenna-like extensions). A bird grabbing for the apparent head end might find its beak sliding off the hard pointed tail end of the beetle, which then could escape by flying away in the opposite direction, its dark color in the shaded forest no longer highlighted against a pale leaf.

Common Meadow Katydid

by Carl Strang

Earlier  I related my error in previously identifying DuPage County’s abundant, early-season large meadow katydid as the common meadow katydid, Orchelimum vulgare. This spring I discovered that the correct ID is the gladiator meadow katydid, O. gladiator. It turns out that the two are physically very similar, and there seemed to be some ambiguity in reference recordings of their songs. Last week I was at Meacham Grove Forest Preserve, mainly in search of late season Pachyschelus beetles, about which more will be forthcoming this fall or winter. Reaching Meacham’s west woods requires a walk across the meadow- and wetland-dominated eastern part of the preserve. Where the trail crossed the preserve lake’s inlet stream, I heard rattling buzzes that sounded like the songs of gladiators. This required some investigation, as gladiators elsewhere had finished singing weeks earlier. I found one, and it proved indeed to be a gladiator. But farther along the trail, approaching the pedestrian bridge over Bloomingdale Road, I heard a different song. This was a loud, tick-and-buzz Orchelimum song, but the ticks were more spaced and the buzz was very tight, making it distinct from the songs both of the gladiators I had just heard, and of the black-legged meadow katydids that also had been singing along the stream. This insect was in a dry meadow, singing from the exposed top of a sweet clover plant.

Common meadow katydid 2b

I photographed him, recorded his song, and then reluctantly collected him. He proved to be a common meadow katydid. The cerci, or reproductive claspers, are distinct from those of the gladiator and just like those in reference drawings for the common. The differences are, however, subtle enough under high magnification that I could not have confirmed them on the live insect. Another difference is the shape of the pronotum, the cape-like structure that covers the top and sides of the thorax. Here is the one on the common meadow katydid,

Common meadow katydid cropped 2b

and here is the one on the gladiator meadow katydid.

Gladiator cropped 3b

Again the differences are subtle, but the side of the gladiator’s pronotum has a simple, uniformly rounded outline with no major zigzags or kinks. That of the common meadow katydid has several turns or bends at the front, bottom and (especially) back edges. Incidentally, there is no mistaking a black-legged meadow katydid for either of the others if you see one:

Black-legged meadow katydid 2b

The best news out of all this is that the songs of these three large meadow katydids of DuPage County’s grasslands and wetlands are distinguishable. The gladiator’s buzz is a long, relatively slow rattling sound, with or without a few preceding ticks. The black-legged meadow katydid has a shorter buzz, of a similar sound quality but distinctly faster, always preceded by 2-4 ticks that are rapid, evenly spaced, and run straight into the buzz. Often, ticks and buzzes alternate in a continuous flow. In my limited experience since first finding the common meadow katydid at Meacham, I have noticed two variations in their songs. The buzz can be very tight and fast, reminiscent of Roesel’s katydid . In that variation the song is very different from both the gladiator and the black-leg. However, some individuals (perhaps ones singing at a lower temperature) have a slower buzz that to my ear is just like that of the black-leg. Confusion is prevented by attending to the ticks. In both common meadow katydid song variations, the ticks are irregularly spaced, farther apart, and more numerous than in the black-leg’s song.

For recordings that may help make these differences clear, check out the Songs of Insects and the Singing Insects of North America websites.

Pachyschelus purpureus

by Carl Strang

 

In recent days I have been describing component communities in two DuPage County forests, and the rules they seem to follow. Today I want to describe an exception to those rules. This is a tiny, wedge-shaped, metallic looking beetle for which I have seen no name in English. Its scientific name is Pachyschelus purpureus.

 

Pachyschelus on Geranium maculatum leaf

Pachyschelus on Geranium maculatum leaf

 

In Maple Grove and Meacham Grove Forest Preserves, I have seen this beetle twice each year (I have seen it in spring at Fullersburg, too). Early in the season they congregate on wild geranium leaves. They scrape little areas off the top surfaces of leaves as they feed, leaving distinctive brown spots (visible in the photo). They reappear in August, but this time feed in the same way on bitternut hickory leaves. Either they go into summer dormancy, or (more likely) have two generations each year, alternating in diet with each appearance.

 

This is a really odd pattern. As I have mentioned, insects that feed on herbaceous plants like the geranium usually must be specialized in their diet because they can deal with only one kind of chemical defense, and each non-woody plant protects itself with a different kind of chemical. This limitation is less true for insects that feed on woody plants like the hickory, because many trees use the same defense, concentrating chemicals called tannins in their leaves. When the leaves are chewed, the tannins grab onto proteins in the leaf tissue, making it difficult for the chewer to digest those proteins. However, the many consumers of tree leaves get around this one way or another, and having done so with one kind of tree often can do so with others.

 

What I described in the previous paragraph summarizes the collective work of many scientists who have looked at hundreds of specific cases. They study insect diets, plant chemistry, draw specific conclusions and then look for general patterns. And for the most part, what I have seen in my study of leaf-eating insects at Maple Grove and Meacham Grove is entirely consistent with established generalizations.

 

But then there is Pachyschelus purpureus. Not only does it eat both an herb and a tree, but as far as I can tell sticks to one kind of herb and one kind of tree only. What it does as a larva I have not found, but I wouldn’t be entirely surprised if there is still more complexity and rule-breaking to be found there. I find it satisfying that so much of the ecology of these forests can be described with discovered rules and patterns. But I also find it satisfying that there are exceptions like Pachyschelus to keep things from being too simple.

%d bloggers like this: