Gypsy moth issues persist, but might soon fade away

Caterpillar stage coming to end 

Gypsy moths are a big topic of conversation in the area right now with the recent infestation bringing a torrent of caterpillars covering walkways, driveways and trees.

A large population of gypsy moth caterpillars in 2020 led to more caterpillars hatching this spring in localized areas across lower Michigan, according to the Michigan Department of Natural Resources.

“I started seeing gypsy moths about five years ago in Mecosta and Osceola counties, but was only finding a couple of egg masses on trees while doing sight assessments,” said Rick Lucas, conservation district forester for Mecosta County. “I knew it was on the landscape, and then it started showing up in more numbers over the last couple of years.

The DNR has determined there are “hot spots” where the county is getting complete defoliation, while a few miles away there may not be any defoliation, Lucas said.

“We have been talking to county commissioners as far back as October to let them know this is coming and asking how they wanted to address it,” he added.

Osceola County commissioner Roger Elkins told the board that the gypsy moth problem is continuing to grow in that county, and suggested the county be proactive in doing something to address it in the future.

"I know our budget doesn't allow for anything, but it is something we will need to address," Elkins said. "Pretty soon we are going to have citizens asking us what we are going to do."

James Kelly, with the Michigan State University Extension Service, said the five-county area he covers — Lake, Newaygo, Mason, Muskegon and Oceana — are all dealing with the problem to some degree.

“Newaygo is the worst right now,” he said. “In Newaygo, there is a campground owner that said his occupancy is down because of it, so it is having an economic impact to some extent, as well.

“It is an issue in the Manistee Forest area, and I am sure there are pockets of Lake County where it is an issue,” he continued.

‘NATURALLY OCCURRING CYCLES’

Experts say the infestation is more of a temporary nuisance than anything else.

“There are naturally occurring cycles and when you have infestations, they seem to be a 3- to 5-year cycle,” Kelly said. “There is no written rule, but generally it could be 3-5 years on and 10 or more years off.

“Right now, we are in the third year, so there is a chance we will see them again next year,” he added. “Some are predicting they will crash after this year, but there are a lot of factors that enter into it.”

DNR forest health experts have said it is likely the populations will crash in some areas while they thrive in others.

Lucas said the cycle happens relative to the numbers of egg masses that were laid the previous year.

“You may have some areas that are miles from the hot spot where they gypsy moth is just starting to invade and it will be at a low occurrence, while at the same time another area may be completely defoliated,” he said.

Lucas said with normal rainfall it would be more predictable to say it would be less next year, but because the area is not getting the rainfall, some areas may begin to decline — others may get worse.

In particular, he said, areas the DNR has termed as “hot spots” where they are getting complete defoliation may be in decline.

“If they are in their second or third year in the center of a hot spot where the insect is going to stress itself out for lack of food and resting areas, those areas could crash this year,” Lucas said. “Other areas are going to continue to build, unfortunately.”

Lucas said they are hopeful in the next couple of weeks they will begin to see signs of the naturally occurring diseases and viruses that cause a population to crash.

“If it follows the typical cycle, we expect some areas to crash this year, which means they will be in the last year that they will have that high population,” he said. “At this time, we are just letting nature take its course.”

The problem will tend to solve itself through natural solutions, Kelly added.

“There is a virus that gets spread amongst the caterpillars, and there is a fungus that grows on the trees, which if the caterpillar consumes it kills them,” Kelly said. “One of the issues is that the fungus needs water to grow and survive, and this has been a really dry spring.”

The Entomophaga maimaiga fungus was introduced into the soil in the 1990s, and has proven to be an effective biological control remaining in the soil from year to year, according to the DNR.

In addition, the Nucleopolyhedrosis virus is a naturally occurring virus that kills caterpillars. It can spread quickly during major outbreaks, causing a population to crash.

These natural enemies of the gypsy moth are now well-established across Michigan and are actively reducing populations. The pathogens have limited the size and length of outbreaks to just a few years, eliminating the need for spray programs, the DNR stated.

Evidence suggests the two pathogens, or diseases that effective gypsy moth caterpillars are causing death, according to MSU Extension. The virus and fungal pathogen levels, which occur naturally, have been increased throughout Michigan.

There are indicators that a population is in decline on its own.

Dead gypsy moth caterpillars hanging in an upside down ‘V’ formation, or in a straight line, indicate the pathogens have affected the caterpillar population.

Evidence of caterpillars having died from these pathogens indicates the local population may be in collapse this year, leading to a lower number next year, according to MSU Extension.

CONCERNS ABOUT DEFOLIATION

Defoliation of trees is one of the main concerns that property owners have with regards to the gypsy moth.

“Trees are completely defoliated in some areas, and that is really what is raising people’s concerns,” Lucas said. “The biggest fear that people have is that all of their trees are going to die. I try to help them understand that we are talking about the same trees today that we did back in the 80’s and 90’s when the first big wave of gypsy moth came through.”

It is only during the caterpillar stage that they do the feeding and cause defoliation, he said.

“For the most part, the trees will do just fine,” he continued. “We have dealt with it before and the trees came through. The one exception would be conifers. If the conifers become defoliated, they will not releaf and most of the time they will die.”

The caterpillars will only feed on the conifer if there is nothing else to feed on, he added.

Kelly said it was a significant talking piece right now and there is a lot of misinformation out there that the trees are going to be dead.

“If it (gypsy moth) was causing the deforestation and the death of trees, it would be a better funded program,” Kelly said. “Because the trees are pretty resilient, it is unlikely that it is going to do a lot of damage to forested areas.”

“Not many trees will die from it,” he added. “They lose a good percentage of their leaves, but it is because of other stresses or other diseases that they typically die. The deforestation looks ugly for a year or two and then things get back to normal.”

Mature forests can normally withstand heavy gypsy moth defoliation with little impact, according to the DNR.

James Wieferich, DNR forest health specialist said gypsy moth caterpillars rarely kill trees in Michigan.

“Only stressed trees suffering from problems like drought, old age or root damage are at high risk,” Wieferich said. “In most cases, gypsy moth caterpillars are more of a nuisance in residential areas on houses and in yards than in the woods.”

Heavily defoliated trees will recover without serious long term effects, the DNR website stated.

MITIGATION STEPS

Residents concerned about mitigating the impact of the gypsy moth on their properties have asked about suppression spraying.

Lucas said he brought the issue to the attention of the Mecosta County commissioners, asking if there was funding to support suppression efforts.

State and county funding that was available in the 80’s and 90’s is no longer available, Lucas said, because the DNR is now aware of a lot of other insects, diseases and invasive species that are far more concerning and there is a lot more demand on available funding.

“It is not that we view the gypsy moth as a minor nuisance,” he said. “We understand it’s impact, however, there are a lot more heavy hitters that are far more concerning such as oak wilt.”

Due to lack of governmental funding, it was determined it would fall upon the local residents to request a special assessment to fund suppression efforts, Lucas said.

“Some areas did choose to spray, but everything was done through the private individual requesting that spraying,” he said. “It was mostly large landowners or property associations that contracted with the private applicators.”

“The federal government is not doing any spraying on federal forest land, so you do get some crossover, which diminishes the effectiveness of the spray,” he said. “The spray is not an eradication. It is a suppression to make the numbers more tolerable and to lessen the impact on the trees for that growing season.”

The best strategy is to spray early in the spring when the caterpillars are young, and follow that up with a walk through to see how many egg masses are on the trees and the sizes of the egg masses, Lucas said.

“Both the numbers and the sizes of the egg masses will tell how effective the spraying was and would be an indicator if the next spring they will be dealing with the problem in the same sense as this year,” he said.

“Spraying could be delaying it, but it can get expensive versus letting it run its course, letting it crash and be done with it,” he added. “It will always be a part of the landscape, but it just might be in so small of numbers that we just don’t notice it as much.”

For residential areas, local governments or property owner associations should conduct surveillance in the fall to determine if populations are reaching an outbreak level, the DNR said. If treatments are needed, aerial pesticide application will target highly infested areas.

Spray programs should seek licensed pesticide applicator businesses familiar with pesticide laws. If you decide to apply pesticides on your own property, be sure to use an EPA-registered pesticide.

There are steps property owners can take to help mitigate the problem, outside of suppression spraying.

“Early in the season, if you look for egg masses and remove them, you can scrape them off into soapy water or burn them, that can actually have a pretty good impact on the local trees,” Kelly said.

“Once the caterpillars hatch, you can put banding in the trees with two sided tape so that they get stuck as they climb up,” he continued. “There are different things that can be done at different times of the year to help reduce the population.”

Anything you can do with collecting the caterpillars, pupas and moths, and destroying them will lesson what will occur the following season, Lucas said.

“Some have said they have millions on their property, and I have seen that first hand,” Lucas said. “That’s not going to be practical to try to pick up every one of them, but if you have a couple of trees in your yard you can have an impact on lessening them.”

Once the caterpillars finish feeding, which will be in the next couple of weeks, Lucas said, they will go into the pupa stage. The pupa then hatches into moths, which breed and leave behind eggs masses. The egg masses can contain from 100 to 1000 eggs.

Mitigation steps can be done at any one of the stages.

“Go through the same process of collecting the pupas and bury them, burn them or put them in soapy water,” Lucas said. “Destroy the moths any way you can, preferably not using a pesticide. Every moth that you can remove will prevent the possibility of reproduction and completing that cycle.”

“You are never going to remove them entirely,” Kelly said. “If you want to try to manage the problem, or just let it run its course, there will be good years and bad years.”

Gypsy moth infestations began in the late 1980’s and early 1990’s, Lucas said, and in the intervening years a lot has been learned about the life cycle of the insect and the impact of infestations.

“The conservation district is taking the lead on providing the latest educational information pertaining to the gypsy moth,” Lucas said. “We are directing people to our website where we have the information assembled. It is helpful to property owners when they can get a better understanding of what the pest is, what it does, and how they can deal with it.”

For more information go to mecostacd.org.

The MSU Extension service also has information about the gypsy moth and what can be done to mitigate the impact on its website at canr.mus.edu.

Information is also available on the Department of Natural Resources website at Michigan.gov/dnr.