Like a B-grade horror film sequel, the aliens have awakened once again. Perhaps we felt a glimmer of hope at the end of the 2020 version when an entire generation of ruthless monsters died off in droves and left us in peace. But remember that closing shot of their disgusting, furry egg-mass blobs cleverly hidden out of sight? Well they’re hatching now.

If you missed last year’s gypsy moth performance, you have a better chance of catching it this season. Unfortunately. Based on egg-mass sampling, the New York State Department of Environmental Conservation predicts that areas which saw moderate to severe gypsy moth outbreaks last year can expect heavy damage this year. NYSDEC’s gypsy moth page can be found here.

Native to Europe, the gypsy moth’s range now extends throughout Africa, Asia, and North America. Its genus, Lymantria, means “destroyer,” an apt designation, and its species name, dispar dispar, reflects the disparate color of males vs. females. It might as well stand for “despair, despair,” since that’s how many of us feel as we watch tree leaves vanish into the maws of gypsy moth caterpillars.

Their introduction in 1868 was especially tragic, as it was deliberate. Étienne Léopold Trouvelot, a French artist, astronomer and so-called scientist, imported gypsy moth egg masses to his Massachusetts home. He thought they could be used to make silk, despite good evidence to the contrary, and without a thought to their potential impact on New World ecosystems. Glass herbariums were safe but pricey, so he raised these fearsome defoliators the woods behind his house. What could possibly go wrong?

Today, gypsy moths are one of the most destructive forest pests in eastern North America, stripping the foliage off at least 300 species of native woody plants. They prefer oaks, but will feed on apple, pine, basswood, spruce, willow, and when population densities are high enough, almost any tree species. In an ironic twist now that EAB is here, gypsy moth caterpillars generally avoid ash. Butternut, walnut and balsam are typically off the menu, too.

Hatchling larvae are black with long hairs, or setae. As the larvae grow, they molt, shedding skins every time they advance to another phase (instar). Later-instar caterpillars develop pairs of raised blue (nearer the head) and dark red (toward the rear) spots along their backs, reaching maturity in early July. After a 14-17-day pupal phase, the adult moths emerge. The mostly-white females can’t fly from where they emerged, and just call out to the boy-moths, which are mottled brown, using pheromone come-on signals. Mated females lay on average around 500 eggs in a “blob” or mass, which they protect with buff-colored hairs taken from their underside.

These oval-shaped egg masses, tan to cream in color and about 0.75 x 1.5 inches (19 x 38 mm), can be found tucked away near whatever hiding spot the female pupated in. Very often laid on tree trunks and notably under flaps of loose bark, egg masses are usually in sheltered spots, but may be just about anywhere. Right now in early May, tiny hatchlings can be found clustered on these masses – it’s a great time to seek and destroy.

Natural predators include blue jays, robins and catbirds, but these have no measurable effect on gypsy moth numbers. The white-footed mouse, the primary reservoir of the three species of Borrelia spirochete bacteria that cause Lyme disease, has redeemed its reputation: it’s the most important vertebrate gypsy moth control, as it loves eating their egg masses. Shrews and other small mammals enjoy hearty breakfasts of gypsy moth eggs, too.

More significant agents are weather, viruses and fungi. As with the tent caterpillar species, prolonged wet, cool weather can lead to hatchling starvation, and a sudden cold snap in late fall or early winter can kill eggs before the embryos inside can winterize their cells. Cool temps also favor infection by fungal pathogens, as explained below.

An endemic soil fungus, nicknamed Entomophaga maimaiga for short, kills gypsy moth caterpillars as their populations rise. But NPV (nucleopolyhedrosis virus) is our MVP when it comes to knocking defoliator numbers down. The catch is that this naturally-occurring virus usually takes two years to precipitate a gypsy moth population crash.

In addition to egg-mass mashing, we can smother eggs that we can’t reach with a shot of dormant-oil spray. This is a very light, highly refined horticultural oil. Some people use aerosol non-stick cooking oil such as Pam, although strictly speaking this might not be legal. (I promise not to tell.)

Applications of Bacillus thuringiensis kurstaki, or Btk to its pals, will protect foliage. Found at any garden center, preparations of Btk contain a natural toxin produced by these bacteria. It is highly specific to caterpillars, and considered safe for other terrestrial and aquatic life. It must be ingested to have an effect. It does wash off, so re-apply after it rains.

Wrapping trunks with a 6” fabric strip, and then smearing it with a sticky compound made for the purpose of trapping insects (Tanglefoot and other brands) will trap larvae, which tend to commute down to the ground at night and back to the treetops in the morning. A “skirt” of burlap tied around trunks will draw caterpillars to take shelter under the fabric, and they can be squished or knocked into soapy water daily. (Caution: the hairs can cause skin rashes and sometimes upper-respiratory irritation.)

Also, never move firewood! Unless it’s from the woodpile to the house – that’s OK. Bringing firewood from home to cottage (or vice-versa) is the best way to spread infestations of all sorts of pests.

Healthy deciduous trees re-foliate after being stripped of leaves, but at great cost to their energy stores. Pines and spruces, though, aren’t endowed with re-foliation powers, and are left with a smattering of green razor stubble with which to photosynthesize; thus gypsy moths can cause such conifer species grave harm. When defoliation occurs in successive years, tree mortality becomes a concern.

Don’t be shy about scouring the back yard in the coming days for egg masses to squish, and it’s probably a good idea to stock up on Btk before the June rush when everyone begins to notice the caterpillars. Let’s hope there’s no remake next year. For more information, see NYSIPM’s gypsy moth resource page.

Paul Hetzler is an ISA-Certified Arborist and a former Cornell Cooperative Extension Educator.

Views: 38


You need to be a member of CornellForestConnect to add comments!

Join CornellForestConnect


Spotted lantern fly in maple stands - effects?

Started by Tim Levatich in Forest Health Sep 9. 0 Replies

Hi, All.I've been reading brief mentions that spotted lantern fly "likes maple". I'm wondering if there is any experience so far with what happens to a forest that has a heavy proportion of maple composition and is hit with a SLF infestation. Our…Continue

Tags: grapes, orchard, fruit, slf, lantern


Started by Mike Blasko in Woodlot Management Jul 28. 0 Replies

I just got a hypo-hatchet to use for beech hack and squirt treatments. The manufacturer states to only use with Amine herbicides only. Is glyphosate an Amine or Ester herbicide?Continue

IPhone surveys

Started by Jim Martin in Woodlot Management. Last reply by Peter Smallidge Jul 13. 13 Replies

Smart phones have GPS.  Has anyone figured out how to use them for mapping wooded land.  I am especially interested in a way to map  my logging trails. Jim MartinContinue

Forester recommendations?

Started by Roger Rodriguez in Woodlot Management. Last reply by Michael Dirac Jul 10. 2 Replies

We are new to forestry ownership and need some advice. We would like to be good stewards of the property and also provide occasional profit of some kind, especially to offset the taxes we pay on the property. I was thinking tree farming (?) as a…Continue

succession after a pine plantation

Started by Jim Martin in Woodlot Management Jun 23. 0 Replies

About 1982 I planted 8000 white pine in a former pasture on the advice of my ex-forester with an OK from the DEC. They got badly weeviled.  I thinned   every third row  and  later also   hit  the most damaged ones which were left.  I hoped to favor…Continue


Started by Chaz U. Farly in Woodlot Management. Last reply by Jim Martin Jun 23. 2 Replies

Is there a reason the State of New York stopped selling hemlock seedlings? I'd made up my mind that I'd like to plant a hundred, maybe more, for my grandsons to enjoy, but find no source. Continue

How long do brush cutter blades work?

Started by Joanne Vaughn in Woodlot Management. Last reply by Joanne Vaughn May 19. 8 Replies

I dunno maybe it's because time flies when it's multiflora rose and buckthorns that are getting whacked. It seems that these blades are needing retirement after 8 or so hours.   Is this typical for this type of material. WIde range of material but…Continue

Tags: cutter, brush



© 2021   Created by Peter Smallidge.   Powered by

Badges  |  Report an Issue  |  Terms of Service