Special Report- The SNE Gypsy Moth Problem

Most residents of South Central Worcester County remember the Gypsy Moth Outbreak of 2016 well.   The Route 16 corridor from Webster to Mendon looked like November in June.  Not every tree was impacted by the invasive species nor was every community.  The drought conditions are directly related to the outbreak.  The caterpillars are back, they are numerous, and they are hungry.  There are some steps residents and business owners can take to protect their property but it will be impossible to protect every tree in Southern New England from these critters.

June 30, 2016, Framingham, MA (photo John Platt)

 A General History
The 2016 outbreak was the first mass gypsy moth outbreak since 1981, but the problem goes back over a century.  The blame can be placed squarely on the shoulders of Etienne Leopold Trouvelot.  Trouvelot was a Frenchman who moved to Medford, MA in the 1850's.  He brought a bunch of gypsy moth eggs with him and tried to raise a colony in the forest behind his house.  Reports indicate he was trying to breed the gypsies with silk moths.  This turned out to be a massive failure as the moths did not breed, but some of the gypsies escaped into the surrounding forest.  It would take over a decade before the severity of Trouvelot's error would be known.  In the 1880's residents complained of lawn damage and in 1890 the MA government passed a bill that provided money for eradication and control of the pests.

Etienne Leopold Trouvelot

The efforts to get rid of the gypsies failed.  However, the moths did not spread from Massachusetts until 1922.  The male gypsies are the only ones who can fly.  The females spend their time laying eggs, which hatch into caterpillars.   Humans are the ones most responsible for transporting the pests.  The eggs are laid in firewood, automobiles, and anything that is left is outside.  Even to this day, the spread reaches as far south as North Carolina and as far west as Minnesota.  It has taken 149 years to travel across half of the country, despite efforts to control the outbreak.

Scientists first tried to kill eggs and spray trees with a toxic spray that consisted of lead and arsenic.  These efforts failed (and probably made a lot of people sick).  Next, scientists tried to introduce some of the natural predators to the gypsies in Europe to the forests of Southern New England.  10 different species that control the population in Europe were brought to America and while it helped a little, mass outbreaks still occurred.  Another problem is that these new predators (mostly wasps and flys) also attacked native North American moths and bugs.  The next spray scientists used was DDT after World War II.  However by the 1960's the effectiveness was minimal, but the harm was large.  Rachel Carson's Silent Spring was a catalyst to stricter government control and regulation of spraying.   By the late 1980's scientists had found pesticides that generally only killed the targeted moths and few other organisms in the forest.

(Sources- http://www.mass.gov/eea/agencies/dfg/dfw/publications/gypsy-moth-outbreak-of-2016.html ) Joe Elkinton and Jeff Boettner of Umass-Amherst

The Gypsy Moth Circle of Life

Gypsy Moth Life Cycle (mass.gov  Bill Byrne)

Like all things in life, the key to kingdom lies with the female gypsy moths.  Females can lay up 600 eggs at a time.  Logic tells us that roughly half of those eggs will be female.  Only 10 female eggs are needed to hatch and survive to increase the local population by a factor of 10 (because each can lay 600 eggs).  The eggs hatch in mid-Spring and grow to about 2" before going into a cocoon in early summer.  After 10 days in the cocoon, the moths emerge.

Controlling the Population
Up until 1989, outbreaks occurred fairly regularly every 10 years or so.  Scientists found correlations between the white mice population and gypsy moth population.  The forest floor rodents love to feast on the eggs so as long as the mice are around, the moth population stays low.  However, the mice population is also highly dependent on acorns.  As native Southern New Englander's know, this can vary wildly from year to year.  Some believe the acorn drop is a sign of what the upcoming winter will bring, but that myth was been debunked.  One solution may be to "introduce more mice to the forest" but the problem with that is mice are territorial.  You won't find more than 50 mice per acre.  The Gypsies can vary from 1-10-100-1000-10000 per acre so the mice are no good to us when the acorn crop is down.

Dr, Ann Hajek of Cornell tried to get a fungus from Japan to take hold in the northeast in the mid-1980's but to little success.  However, in 1989 the fungus spread throughout the northeast and researchers noticed dead caterpillars all over their research sites.  Researchers help spread the fungus but it also spread on its own.  The fungus kept gypsies at low levels for 35 years and it seemed to have solved the problem.  This fungus is called Entomophaga maimaiga where maimaiga is Japanese for Gypsy Moth (the more you know).

A dead Gypsy caterpillar from E.M (NCbuy.com)

Then 2016 happened.

The 2016 Southern New England Gypsy Moth Invasion

MA Department of Conservation and Recreation, Forest Health Program 

The roots of the 2016 outbreak can be traced directly May of 2015.  Entomophaga Maimaiga thrives under rainy and cool conditions between May 1-June 20 of a given year.  Here is the rainfall from May 1-June 20 of 2015 and 2016 compared to average and to 2017 (to date).

We are off to a good start in 2017 and there is more to come this weekend.  After the rain this weekend we will be near or above the 50-day totals from 2015 and 2016 in just two weeks.  This will not save us in 2017, but it can in 2018.  We had more rain in April this year and a bit more in the winter which has increased ground water and soil moisture.

US Drought Monitor 2nd week of May 2015, 2016, 2017

In summary, Trouvelot introduced them, efforts to control them for years failed until Dr. Hajek introduced Entomophaga maimaiga in the mid-1980's.  It took a few years but from 1989-2015 there were no widespread gypsy moth outbreaks in Southern New England.  Drought and warm weather limited the E.M. in 2016 and the caterpillars ate away a lot of foliage in South Central and Southeastern SNE.

Enough History and Science How Do I Protect My Shade?
Some in RI want the government to conduct aerial spraying in order to protect the foliage.  Some states do it, but experts at Umass-Amherst warn against it, preferring to let mother nature do her work.  That said if you have a rare tree in your yard such as a Japanese Maple, Dogwood, or really any shade tree it makes sense to hire a license spraying company to protect your investment.  These companies will use Bacillus thuringiensis kurstaki (Btk) which specifically targets caterpillars  The Btk releases a protein that is lethal to caterpillars alone, leaving the tree and other bugs and insects safe.

Here is a PDF from the Mass DCR with some more information on the gypsy's and prevention later this summer and fall.