Flame-shouldered Dart

by Carl Strang

Old notes, photos and memories are worth recording and keeping, as they can produce results as new information becomes available to illuminate them. Back in the 1980’s as I surveyed plant-eating insects in Maple Grove and Meacham Grove Forest Preserves, I was able to identify most of the species I encountered, but I tried to get photos of all, and kept notes and records. That research introduced me to the important component community concept. This is the idea that each kind of plant (or each group of plants that use similar chemical defenses) is consumed by a particular suite of insects and other herbivores adapted to defeating those defenses, and this is a helpful way to organize many of the species in a forest or other community. One of the component communities in the study forests was based on Smilacina racemosa, the feathery Solomon’s plume or false Solomon’s seal.

Feathery Solomon’s plume

Feathery Solomon’s plume

In one of the first posts in this blog I described that component community, and mentioned that I was unable to identify two of its members. Later I found a resource that allowed me to narrow down one of the mystery insects, a sawfly, to genus Phymatocera, either P. offensa or P. similata.

One of the Phymatocera sawflies consuming Smilacina flowers

One of the Phymatocera sawflies consuming Smilacina flowers

Recently I ran across a photo in the excellent Wagner guide to caterpillars that allowed me to identify the other unknown. It proves to be the flame-shouldered dart (Ochropleura implecta), a moth in the owlet moth family Noctuidae.

Flame-shouldered dart caterpillar on Smilacina

Flame-shouldered dart caterpillar on Smilacina

As is the case with many noctuids, however, this one has a fairly broad diet across its range, so its presence on this particular plant provides only a little information. Nevertheless, it’s always nice to solve an old mystery.

Sawfly Near ID

by Carl Strang

In the 1980’s I was inventorying the leaf-eating insects of two forested study areas, at Maple Grove and Meacham Grove Forest Preserves. I was able to identify most of the insects I encountered, but one of the common ones eluded me. It was a sawfly caterpillar that ate the flowers, berries and, at need, leaves of Solomon’s plume (Smilacina racemosa).

This is the sawfly caterpillar in question. Note the head and leg color; these turn out to be important.

Sawflies are herbivorous members of order Hymenoptera (bees, wasps, ants, etc.). One seldom encounters the adults, and the more conspicuous larvae are wretchedly difficult to identify. I tried rearing them, but they overwinter in soil and successful maturation in captive conditions is rare.

Last week on a whim I did a search on “sawfly Smilacina racemosa” and turned up something in Google Books [Smith, David R. 1969. Nearctic sawflies I. Blennocampinae: adults and larvae (Hymenoptera: Tenthredinidae). Tech. Bull. No. 1397, Agricultural Research Service, U.S. Dept. Agriculture]. If I were an entomologist I probably would have found this back in the 80’s, but thanks to the Internet even an amateur can find such references now.

It was an embarrassment of riches, of sorts. It turns out that there are 5 species of sawflies in the genus Phymatocera that are associated with this plant, and all occur in Illinois. Adults can be identified to species, but the best one can do with larvae is narrow them down to 2 or 3 of the species. There is a larva “species 1,” with black heads and legs that contrast in color with the body; three of the 5 sawflies in question are thought to belong to this type. As you can see in the above photo, the larvae I find have brown heads, and legs the same color as the body, and so fall into the “species 2” larval category. So, it would appear that my bug is either Phymatocera offensa or P. similata. The first of those two has in fact been reared on Solomon’s plume in Illinois, while adults of the other have been caught in sweep samples taken from the plant. Makes me think I should try rearing them again, if I can find the time…

More Mayslake Fruits

by Carl Strang

Earlier I featured several plants at Mayslake Forest Preserve that produce fruits timed to coincide with the fall migration of berry-eating birds. This mutualistic interaction for the most part benefits the birds, through nutritional provisioning, while the plants get their seeds dispersed. Today I want to feature some outliers to this pattern. Let’s start with Solomon’s plume, also known as false Solomon’s seal.

Solomon's plume fruit b

Like many fall fruits, these advertise themselves to birds with a bright red color. When analyzed, however, the berries proved to be junk food, or perhaps are more accurately described as food mimics (White and Stiles 1985, Ecology 66:303-307). The plants save their energy, investing no nutritional value in these fruits. The ruse works, apparently, by exploiting the naïve instinctive response of first-time autumn migrants, the young of the year. A little different from this is the offering of the European highbush cranberry.

European highbush cranberry fruit b

Another study (Witmer 2001, Ecology 82:3120-3130) showed that the nutritional value of these berries becomes available only when they are consumed along with a significant protein source. I was impressed to learn that, like the waxwings native to the shrub’s European home, our North American cedar waxwings ignore these tempting berries until spring, when cottonwoods or other poplars are flowering. Then the birds consume the berries along with cottonwood catkins, protein in the pollen providing access to the berries’ nutritional value.

Common buckthorn fruit b

These black berries are common buckthorn fruits. They generally are ignored by birds until late winter when, apparently, the better quality foods have been depleted. Then, robins and waxwings consume them, unfortunately dispersing the seeds throughout our woodlands. Buckthorns leaf out early and lose their leaves late, casting a shade so dense that no other plants can grow beneath them. This is why these Eurasian shrubs must be removed at the beginning of woodland restoration projects. A final fruit is of no interest to birds.

Buckeye fruit 2b

Ohio buckeyes in fact are largely ignored by animals generally. This opens the possibility that, like other trees I discussed earlier, buckeyes may have been dispersed by now-extinct mastodons and other large herbivores.

Component Communities: Solomon’s Plume

by Carl Strang

 

Continuing yesterday’s subject, I want to focus on the component community centering around Solomon’s plume, another flowering herbaceous plant of DuPage County woodlands. I prefer the English name fostered by the Morton Arboretum rather than the more widely used “False Solomon’s Seal.” Smilacina racemosa is the poetic sounding scientific name.

 

smilacina-with-sawfly-b

 

This perennial member of the lily family produces its cluster of little white flowers at the tip of its stalk in early summer. The name “plume” refers to this cluster. The flowers develop into speckled berries that ripen in the autumn, just in time to fool the migrant birds (they have practically no food value, and are best thought of as food mimics, but that’s a story for another time).

 

I found several insect consumers of this plant in the 1980’s (deer also feed on it as the stalk sprouts up in spring). The earliest is an uncommon large caterpillar, probably in the Noctuidae family, which consumes flowers and possibly fruits in their early development.

 

caterpillar-on-smilacina-b

 

As the fruits begin to form, a sawfly caterpillar appears and begins to eat them. This common species, larva of a wasp relative rather than a butterfly or moth, often consumes all of a plant’s berries, then works on the leaves.

 

sawfly-larva-solomons-plume-b1

 

Sawflies are notoriously difficult to rear to adulthood, and I have not yet identified the species. Finally, in July, there is an unidentified leaf miner which produces a winding linear mine but did not interact to a measurable degree with the sawfly.

 

The biggest impact on the plant was caused by the sawfly. In 1983, 23% of stalks had fruit at Maple Grove, and 33% at Meacham Grove. Sawflies occurred on 88% and 93% of fruiting stalks, respectively, and removed averages of 41% and 74% of the fruits.

 

Once the leaves have matured they are relatively safe from herbivores, the leaf miner alone able to specialize on that resource. Scientists have found that plants defend their tissues with chemicals that poison or at least interfere with the digestive systems of their potential consumers. Herbaceous plants are more varied in their chemical defenses than are woody plants. This means that their associated insects tend to become specialized in their diet, able to evolve ways to deal with one kind of poison produced by a single plant or group of closely related plants. A result of this is the component community structure I described yesterday, with each kind of plant hosting the few consumers that have solved the puzzle posed by its defenses.

 

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