On The Trails: Beach rye, ergot, and flies; cottonwoods and leaf beetles (and lots of questions)

Cottonwood leaf beetle larvae scrape a layer of foliar tissue, leaving scars below. (Photo by Bob Armstrong)

By Mary F. Willson

In late summer we usually notice dark "spurs" sticking out of beach rye inflorescences. That is a spore-bearing part of the ergot fungus (Claviceps purpurea) that infects rye flowers.

When mature, it drops to the ground to overwinter, the asexual spores germinate, producing tiny mushrooms that make sexual spores that are dispersed on the wind, often landing on rye flowers. There they germinate, making a soft white mass that drips "honeydew" containing another generation of spores. Those spore-laden drips may be picked up by insects, or whisked away on a breeze, or attached to a passing animal, and eventually passed on to another beach rye flower, to start the cycle again. This fungus can also infect other species of rye, including domestic crops, and sometimes other grasses.

Ergot contains nasty poisonous alkaloids that, when the infected seeds are ingested, have serious effects for mammals and at least some birds. Those toxins can cause convulsions, hallucinations, seizures, and sometimes death, as well as constricting blood vessels, impairing circulation, and thus leading to dry gangrene and loss of body parts. The same toxic chemicals also have medicinal uses (if used carefully). The honeydew is not toxic to insects that forage on the flowers. 

Other species of Claviceps are also toxic, capable of infecting the seeds of a variety of plants, particularly those called monocots (flowering plants that have one embryonic leaf when the seed germinates, instead of two such leaves), including corn, sorghum, etc.

Ergot fungus spore capsules stick out of beach rye and will later drop to the ground. (Photo by Bob Armstrong)

Recently, a local naturalist-photographer noticed that beach rye inflorescences in some places (such as Eagle Beach campground) harbored clusters of dead and moribund flies (probably mostly blowflies, whose maggots enjoyed the many salmon carcasses nearby). The flies had swollen abdomens, a symptom of an infection by the lethal fungus Entomophthora muscae. But what drew those dying flies to beach rye in particular locations — something about the location, or characteristics of those specific rye plants, or ???. The flies do not seem to be drawn specifically to rye plants with spore-bearing spurs, but we don’t know what happens in the early (not easily detectible) stages of an ergot infection or, for that matter, with flies with early stages of that infection. So we still don’t know why those flies land on rye plants — just in some places. Lots of questions!!

Beach rye is also known by several other common names, including dune grass. After some reorganizing and shuffling, its current scientific name seems to be Leymus mollis. A perennial, it is distributed in northern North America and Asia.

Out at Eagle Beach campground, some friends and I looked at a small cottonwood tree that had been seriously attacked by leaf-beetles known as Chrysomela scripta. There can be several generations per year. Adults lay masses of eggs on the undersides of leaves. Larvae hatch in a couple of weeks, feed in groups for another two weeks or so, skeletonizing the leaves in the process and sometimes eating all but the midrib. Young larvae scrape off leaf tissue, but older ones can chew holes. Then they pupate somewhere nearby. Adults emerge in roughly a week or so, then chew on foliage and buds. The last generation of adults each year overwinters and emerges in spring.

On their backs, the larvae have rows of little white lumps that mark the location of scent glands. When a larva is disturbed, those scent glands emit an odor that’s described as pungent. Presumably this helps deter predators such as ladybugs, lacewing larvae, some ground beetles (and sometimes ants), and parasites including certain wasps and tachinid flies.

Some of the same questions asked about beach rye and flies can be asked about cottonwood leaf beetles. Why was this particular cottonwood so heavily attacked — is it location, or something genetic or acquired by that individual, or ???.

Dead flies on beach rye died from fungus infection (not ergot). (Photo by Bob Armstrong)

Our little field trip to Eagle Beach was profitable in another way. We were searching for a special fungus that likes to grow on bear scat. It had been seen here earlier, but on this day, the hunt took a while. Eventually we found a bear scat with lots of very small, very young fungi. These will eventually turn into elegant white mushrooms of some taxonomic interest. A close relative is known to occur here, so the question is if this is a new species or the known one. That will take some DNA analysis.

• Mary F. Willson is a retired professor of ecology. "On The Trails" appears periodically in the Juneau Independent.