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Ghost moths & dead spruce.

This elusive insect, abitted by acid rain, may be pushing some forests over the edge.

Armed with carrots, plastic party cups, and antifreeze, Dave Wagner and his crew hike three miles in the freezing Vermont rain on a blustery day in june to the top of Camel's Hump Mountain. From there, they move off the Burrows Trail several hundred yards and begin bushwhacking back down through the soggy conifer forest. Stopping at every 200-meter (650-foot) drop in elevation, the rain-suited researchers bury carrots under the pine- and fir-needle litter. They also dig holes, half-fill several party cups with antifreeze, and place the cups in the holes so that the rims are flush with the forest floor. In the dank cold, swirling fog, and stinging wind, it takes six hours for the group to complete its task.

In this first field experiment of the season, Wagner, an assistant research professor in the Plant and Soil Sciences Department at the University of Vermont (UVM), hoped his antifreeze cocktails and carrot bait would trap larvae of the conifer swift moth. The larvae were supposed to stumble along and fall into the cups, where they would be killed and preserved by the antifreeze. As for the carrots, well: Once a swift-moth larva finds something as delectable as a carrot, it's not likely to move on until that carrot's gone," says Wagner.

Wagner's quarry, a nondescript, drab brown moth virtually unstudied until a few years ago, may be helping to kill trees in the high-elevation forests of northeastern America. The trees, principally red spruce, have been dying in distressing numbers for years, and the experts don't know why.

Foresters first became aware of the steady and ubiquitous decline of the high-elevation conifer forests in the late 1970s. "That was when we realized we were losing red spruce at an astonishing rate," says Hubb Vogelmann. Vogelmann, chairman of the Botany Department at UVM, has tracked the declining tree populations on Camel's Hump since 1979.

What's happening on Camel's Hump, however, is representative of a much larger picture. High-elevation stands of red spruce are in trouble throughout the Appalachian range, from Mt. Mitchell in North Carolina to the slopes of the Adirondacks, Green Mountains, White Mountains, the mountains of Maine, and on up into Canada.

Wagner and his colleagues find the conifer swift moth living in forests ranging from the highest peaks of the southern Appalachians north to Labrador and west to Alberta, including all areas where foresters have identified red spruce as declining. Although the larvae will eat a wide variety of plants, they consider red spruce roots a delicacy and are most abundant in red spruce stands. Wagner's average count of 10 larvae per quarter square meter translates to an estimated 160,000 larvae per acre; he has observed as many as 40 larvae per quarter square meter. Pale, squirmy, and voracious, a mature larva can reach 11/2 inches in length.

In laboratory experiments, the researchers find that a single larva can kill a red spruce seedling. In the field, young larvae essentially girdle saplings. Older larvae gouge wounds down the length of the roots of mature trees. In the areas of high larval densities often corresponding to the areas of most severe decline-feeding wounds pepper the roots of the trees.

In some forests, more than half of the standing red spruce have died. The rest show various signs of ill health. Much of the blame is placed on air pollution, particularly the phenomenon known as acid rain. Although most scientists do not dispute that acid rain can destroy ponds and lakes, the jury is still out on whether acid rain can, in fact, kill trees.

"Pollutants are playing a role," asserts Jerry Hertel, manager of the Spruce-fir Research Cooperative, a program set up by the U.S. Forest Service to fund research on spruce and fir decline. Just which ones and how they might be playing a role is still open to debate.' What it looks like, says Hertel, is that air pollution doesn't damage trees directly, but acts in conjunction with other factors such as weather and insects. That's where Wagner's carrots and party cups come in. The conifer swift moth, spurred on by acid rain, may be pushing some forests over the edge.

Why weren't the moths noticed until now? "Not much research had been done in these high-elevation forests, because from an economic point of view they weren't that important," says Hertel. -The research that had been done dealt with the above-ground system. You start getting down to the roots and digging them up, and that's a big job. The moth's probably been there for a long time-it's just that nobody ever looked for it.'

The only previous record of anyone looking for the moth dates back to 1865, when an entomologist named Packard described the species and, ironically, noted that it might be feeding on red spruce roots. After that brief coming out over 100 years ago, the conifer swift moth remained in the closet until 1982, when two graduate students of Vogelmann's noticed the larvae occurring in large numbers in their plots on Camel's Hump. Their observations eventually came to the attention of Bruce Parker, professor in the Plant and Soil Sciences Department at UVM, and Bill Wallner, principal insect ecologist for the U.S. Forest Service at the Northeastern Forest Experiment Station in Hamden, Connecticut. Wagner, one of the world's foremost authorities on swift moths, joined the project in May 1987.

According to Wagner, the conifer swift moth belongs to a primitive family of moths known by two names-swift moths and, more commonly, ghost moths. The name "swift moth" refers to the moths' quickness in flight. Wagner says a British specialist told him that you can identify swift moths by "the little sonic booms you hear when they fly by your head." Wallner likens attempts to catch conifer swift ball.

As if to compensate for their frenzied traveling habits, ghost moths fly only during short periods at dawn or dusk, typically for no longer than 30 minutes. The monicker "ghost moths" comes from a British species whose males have a striking silvery-white coloration. At evening twilight, the males swarm in groups of up to 2,000 individuals. The poor soul coming across such a shimmering, oscillating cloud of moths "probably wouldn't care to get close enough to find out it was an insect," says Wagner. Appropriately, the apparitions often occur in cemeteries.

Aside from dazzling entomologists with their speed and strange behavior, several species of ghost moths are familiar as severe pests worldwide. In Japan and China, they attack over 200 types of plants. In Great Britain, ghost moths have ruined carrot and potato crops. In New Zealand, Australia, and South America, the moths can devastate pasture lands. In these pastures, researchers have correlated the practice of fertilizing with ghost moth outbreaks. ability limits the reproductive success of almost all insect populations, particularly those feeding on plants. He thinks that acid rain might act as sort of an insect fertilizer, allowing the moths to reach densities where they cause irreparable damage to the trees.

Another possibility, says Wagner, is that the larval feeding wounds allow pathogens not normally able to penetrate healthy trees to gain toeholds from which they can go on to kill the trees.

But, except for the few well-known pest species, ghost moths remain an obscure group of insects. Ghost moths in general exhibit unusual biological characteristics that make them difficult to study, and this is perhaps another reason forest-decline investigators overlooked the conifer swift moth for so long. Populations of the moths tend to be locally abundant-often plentiful in spots-but rare in adjacent areas. Because they fly only during short periods at dawn and dusk, when it is difficult to see, the adults are easily missed. In addition, the adults do not eat and lack functional mouthparts. They don't go to flowers for nectar, or to water to drink-places where other moths are commonly observed. And because they live underground, the larvae are even more inconspicuous.

The conifer swift moth makes no exceptions to these rules. Hidden from the entomologist's inquiring eyes, a conifer swift moth spends its first two years of life underground as a larva. The adult stage, by contrast, is very short. Adults court, mate, and die within a week after emerging in July.

But conifer swift moths have yet another biological quirk that makes them even more inconspicuous than other ghost moths. Every other year, they go through a boom-and-bust cycle. In Vermont, the adults emerge and fly only in even-numbered years. But the phenomenon flip-flops across North America-in Nova Scotia and Wisconsin, the adults fly in odd-numbered years. So if you search for larvae in a year when adults are flying, you probably won't find any. Likewise, you'd have a hard time finding adults in an off year when most individuals are still in the younger larval stages.

Wagner and the others hope that understanding how this elusive moth fits into conifer forest ecology will give them eagerly sought answers about the relationship between forest decline and acid rain. Biological factors such as the moth must be examined carefully, says Wallner, before the chemical factors can be sorted out. "Certainly you can point your finger at acid rain, but before you bang the final gavel, you'd better look at the total picture in terms of what that biological component is doing," he says.

Everyone, however, cautions against oversimplification. Bob Bruck, professor of plant pathology and forestry at North Carolina State University, says he hasn't found ghost moth larvae in his plots on Mt. Mitchell, and the red spruce there are dying just as they are in the Northeast. He compares forest decline to cancer. "Cancer isn't a disease- it's hundreds of diseases," he says. "In forest decline, we are not dealing with a pollutant or a moth. We're dealing with hundreds of things acting simultaneously, synergistically, and/or antagonistically in creating the scenarios we see. It's a very irresponsible act for anyone to come out on any side of this issue with any type of definitive statement.'

And according to Vogelmann, many foresters believe that forest decline is just a cyclical phenomenon and not something we need to worry about. "They say we don't know enough about the history of our forests, which change over hundreds of years, and we're seeing just a little blip here."

But while the authorities sort out whether or not there is in fact a forest decline problem and whether acid rain is or isn't involved, conifer swift moth larvae munch steadily away at red spruce roots and the steady supply of carrots Wagner tempts them with. "Conifer swift moth larvae are without a doubt the most conspicuous organism in these soils ... I mean you see them over and over again," says Wagner. "Their role in forest decline, especially in the death of red spruce, has not been clarified, and it needs to be.' AF
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Title Annotation:red spruce pests
Author:Egerter, David E.
Publication:American Forests
Date:Jul 1, 1989
Words:1832
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