Gypsy Moths in Rensselaer County

Gypsy Moths in Rensselaer County

 by John Leahy (Eastwick Press, June 2, 2006)

Spring is well established in all its bright green glory and the trees are covered in a new coat of leaves. Or are they? While driving down the road or even strolling through your own yard, you may have noticed trees that seem naked and bare of leaves. These denuded trees you see may well be victims of one of the most devastating forest pests in North America, a scourge called the gypsy moth. As spring shades into summer, government scientists and property owners alike speculate at the impact that this year’s population will have.

The gypsy moth was an indigenous species to Europe and Asia and was imported to the United States in the 1860’s by Leopold Trouvelot who was trying to cultivate silk worms to produce silk. In 1869 the caterpillars escaped from his back yard in Medford, Massachusetts and within decades they were defoliating large tracts of New England. For more than a century, government agencies at the State and Federal levels have been monitoring and attempting to control the expansion of the gypsy moth population range that now extends throughout the northeast and as far as the Midwest and North Carolina.

The gypsy moth feeds on tree leaves and particularly favors oaks, but will also devour beeches, hemlocks, maples and pines, all common species in our local forests. The one common tree that seems not to appeal to it is the ash. The gypsy moth can completely defoliate a tree, stressing it by depriving it of the ability to photosynthesize. If the tree is defoliated in early summer, it will often put out a whole new set of leaves.

Although the general population keeps expanding its geographic range, the local population may fluctuate greatly from year to year. These yearly fluctuations are highly dependent on such factors as weather, availability of desirable food species, population sizes of predators, and the comparative abundance of other desirable food species for these predators. When suitable weather conditions prevail, combined with abundant food and low predator stress, the gypsy moth population can boom unchecked in a spike that will ultimately bust and collapse as the inflated population consumes its food source and starves itself back down to more normal levels. In the meantime however, the host trees may have been stripped of their leaves.

The NY State DEC says the jury is still out on how this summer will shape up for the gypsy moth in our local area. According to Jason Denham of the DEC Land & Forests Division, there has not been much evidence of real significant defoliation yet but they have only surveyed in the Albany area and have not yet toured Eastern Rensselaer County. The main method of attempting to quantify an estimate of the coming population is to look for egg masses on the trees during the winter. This method is empirical rather than rigorously precise and serves to give a yes/no – significant or not significant – estimate about the coming population. From surveying this spring, DEC estimates that the development of the gypsy moth population is progressing at its approximate normal schedule. Due to this spring’s weather pattern, the egg to larvae growth sequence had been about three weeks ahead of normal schedule until the recent rains came, but the effect of the heavy rain has been to depress development and the progress is now back to its normal track. Denham explained that DEC typically performs an aerial survey from mid June through mid July to most effectively capture defoliation after trees have all leafed out and before defoliated trees have had a chance to refoliate.

Another forest pest that is often confused with the gypsy moth is the eastern tent caterpillar. These are the caterpillars that build the highly visible silk tents in tree limbs crotches during spring. The eastern tent caterpillars can also cause tremendous defoliation damage, although they usually do not cause tree mortality and are more of a nuisance for aesthetic reasons. The eastern tent caterpillar favors fruit trees such as cherry and apple.

The New York State DEC and the US Forest Service both offer information about the gypsy moth and other tree pests like the tent caterpillars.