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Talk to me, tree! Gypsy Moths in the Shenandoah Valley

Gypsy Moth CaterpillarChasing gypsy moths in the Shenandoah Valley of Virginia is still at the top of my list of fun jobs! The moth is an invasive species whose ravenous larval form marched across the state in a destructive swath of defoliated forests. The caterpillars threatened to destroy valuable veneer-quality trees of the Appalachia Mountains and disrupt the delicate ecology of the headwaters of the Shenandoah River. The State of Virginia and the United States Forest Service hired me and other biologists and foresters to survey the population of the moth, manage affected areas, and share with the community operative but environmentally sensitive ways to deal with the bugs. This lepidopteron invasion was much more than a nuisance. Being exotic, the caterpillars had no natural predators in America. Thousands hatched unchallenged from a single egg mass no bigger than a thumbprint and a solitary tree could have hundreds of masses. They hatched about this time of year, just after the first leaves emerged in spring. Little bits of unconsumed leaves fell constantly like green confetti, glistening in the sunlight as shade gradually disappeared from the forests. That wasn’t the only thing that dropped from the trees. Like tiny peppercorns, insect frass rained down from the canopy. In the quiet of the forest, one could actually hear the sound of munching! Communities in the valley and in the mountains declared war on the gypsy moth. They set traps made from burlap sacks, reported new infestations, and before the crack of dawn they volunteered to release helium balloons to mark areas to be treated aerially. But the invasion was almost over-whelming. Windshield wipers, hoses, and brooms were kept busy clearing off the disgusting debris while homeowners witnessed the sad denuding of their gardens. By July, the landscape looked like winter! Using a compass (early 1990’s – before GPS was readily available to the public) and a topography map marked off in one-kilometer grids, my job was to survey the mountainous terrain to access the damage by counting egg masses, measuring the defoliation, and setting pheromone traps to sample the population. Along the boundary of newly infested woodlands, I observed an interesting phenomenon. Several times I noticed a ring of unaffected oak trees surrounding a single infested oak. This did not match the gypsy moth’s natural history. They moved across the forest by dangling from a rather hardy silk and letting the wind take them from tree to tree. Like the wind, infestations were usually linear in direction. The strange pattern that I saw on the ground was, indeed, confirmed in aerial photographs. I solicited my colleagues for an explanation and the one who I respected the most, a retired U.S. Forestry Service veteran who spent the better part of his life in the woods, replied rather flippantly, “Yeah, it warned the others in time for them to kick in their defense mechanisms.” The comment was followed by a long and awkward silence. The others in the room, seeing that I would not let it go and fearing yet another hour-long lecture from the old forester stood behind him and frantically waved their hands in an effort to stop me from asking, “How?” The forester looked at me in disbelief, the way he always did when he thought I should know the answer. He couldn’t resist, “What did they teach you in college?” Finally, after a poignant shake of his head he drew his face too close to mine. Accentuating every word he whispered in my ear, “They talk to one another!” To that response, most people would have smiled politely and walked away. Not me. This man had something no textbook would ever give me – years of boots-on-the-ground knowledge of the forest. I believed him and delved into the research to find out more. Trees are not passive when attacked. When an oak tree is assaulted, it releases a chemical message into the soil through its roots. Symbiotic fungi that grow around the roots absorb the chemicals and, either deliberately or inadvertently, passes the warning message from one tree to another. In response, the uninfected oaks secrete more tannin into their leaves. Insects don’t like the bitter taste of tannic acids. Vegetation communication! So cool! This introduced moth is now a part of the east coast forest landscape. Through careful integrated pest management and natural selection, the population of the gypsy moth has stabilized in Virginia. Visitors to the Skyline Drive and the Appalachian Trail can still see a few old snags (dead trees still standing), reminders of that initial and devastating invasion. Two decades have past since I first learned that trees could “talk”. So it was interesting to read this article today. Check it out! By the way – do say a kind word to your houseplants. You never know, they might be listening!
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