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By Root 726 0

in contrast, been very difficult to find. All the students who hunted Calosamia in Maine are ardent field naturalists. One of their academic requirements—one that they find easy to fulfill—is their “Friday field walk” in the surrounding Vermont woods. For the last ten years they have been assigned to find Calosamia cocoons. I had found none; they found four. Three of the cocoons had successfully eclosed moths, and the fourth contained viable Gambrus pupae. Calosamia still live, but at very low densities. Perhaps the density of Calosamia is so low in Vermont that disease organisms and parasitoids have a hard time finding them, but the moths can still find each other to mate.

The males’ female detectors are evolved to what looks like extraordinary perfection. In early June 2004, 2005, and 2006, my screen cage in Vermont containing moths from cocoons that I had collected in Maine was aflutter with freshly emerged moths. I did not release them, because I was hoping to get eggs for a crop of caterpillars. The day after they emerged, at around six PM in bright sunshine, the big magenta males “with a bolt of lightning crackling down their wings” as one moth aficionado described them, were flying all around our house. It seemed that a swarm of them had gathered. Males were again flying around the house the next day, in the late afternoon, but by the day after that I saw no more of them.

I next hoped to raise caterpillars from the eggs laid by the mated females.

Using a thread looped around their “waist” I had tied females onto both ash and chokecherry bushes, and each of these mated females deposited about 100 to 200 eggs onto the leaves and twigs there. Freshly laid eggs are sticky and become glued onto the substrate. I checked later, expecting the bushes to be crawling with caterpillars, but found not a single one. In the third summer I took the mated females into my study and let them deposit their eggs in screened cages so that I could keep track of them. All the eggs hatched, and hundreds of young caterpillars started feeding on the ash leaves I had provided for them. Then, soon after their first or second molt, they all died—every single one. Not since I raised caterpillars as a small child, when a fellow student zapped my screened caterpillar cage with spray from a Flit insecticide dispenser, had I seen such caterpillar mortality. The signs this time pointed to death by a virus. I noticed also that the few gypsy moth caterpillars that I had found near the house in Vermont died as well; they turned into a liquid broth.

Fig. 24. Various contents of Calosamia cocoons. Left: An empty cocoon chewed into by a rodent. Top left: Mummified caterpillar killed by a mold. Top right: Cocoon of the Enicospilus wasp, showing a hole at top where it emerged. Lower left: Cocoon packed with numerous Gambrus wasp cocoons. Lower right: Cocoon showing the pupal skin of a successfully emerged moth.

The gypsy moth, Lymantria dispar, is a forest defoliator in North America. It evolved in Europe and Asia and was introduced near Boston in 1868 by E. Leopold Trouvelot; and, as they say, “The rest is history.” It became such a serious forest pest in all states east of the Mississippi that state and federal governments instigated eradication attempts, spraying millions of acres of forest with pesticides and also releasing biocontrol agents that have included viruses, bacteria, fungi, a beetle, and fly and wasp parasitoids. Some of these biocontrol agents affect the gypsy moth specifically. Unfortunately, others have a broad spectrum, attacking so-called nontarget species of native moths and butterflies.

Recent studies by George H. Boettner and Joseph S. Elkinton, entomologists at the University of Massachusetts-Amherst, have demonstrated a deadly effect of one of those gypsy moth biocontrol agents on the caterpillars of these moths. It is a parasitoid fly, Compsilura concinnata. This fly alone “controls” at least 200 species of moths. “It is,” Boettner told me, “an evil beast that should never have been released.” Are there also evil beasts