Northern WI Forest Health

Sawflies On Jack Pine Are Neodiprion Maurus

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Photo showing five Neodiprion maurus larvae feeding on jack pine needles.

Neodiprion maurus larvae, feeding on jack pine, are gregarious. Can you spot all five larvae? / Photo Credit: Wisconsin DNR

By Linda Williams, DNR Forest Health specialist, Woodruff
Linda.Williams@wisconsin.gov or 920-360-0665

In mid-July, a few sawfly larvae were found feeding on jack pine in northern Vilas County. After delving into associated literature and reaching out to a sawfly researcher at the University of Kentucky, the sawflies were identified as Neodiprion maurus. There is no official common name for this insect; it is generally referred to as “a sawfly on jack pine.”

These sawflies are gregarious and feed in groups on older needles, doing relatively minimal damage. They are often referred to as “rare” and have been found in Michigan, Minnesota and Wisconsin, as well as Alberta, Manitoba and Saskatchewan in Canada.

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Pink Striped Oakworm Seen Feeding On Red Oaks

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Closeup photo showing young pink striped oakworm caterpillars feed gregariously on northern red oak leaves.

Young pink striped oakworm caterpillars feed gregariously on northern red oak leaves. / Photo Credit: Wisconsin DNR

By Linda Williams, DNR Forest Health specialist, Woodruff
Linda.Williams@wisconsin.gov or 920-360-0665

Young larvae of the pink striped oakworm (Anisota virginiensis) have been observed feeding gregariously on northern red oak leaves in Vilas County. Northern red oak is their preferred host, but they can feed on other oaks.

Young caterpillars start life with a shiny black head capsule, but older larvae develop an orange head. Their pinkish body coloration develops as they get older, as well; young caterpillars are dark green in color.

Pink striped oakworm has several fly parasitoids, along with a couple of wasp parasitoids. Populations of pink striped oakworm in Wisconsin don’t usually grow too large or cause problems.

 

Northern Pitch Twig Moth Creates Pitch Blisters On Jack Pine

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Closeup photo showing that hollow pitch blisters get darker with age and may resemble cones until closer examination.

Hollow pitch blisters get darker with age and may resemble cones until closer examination. / Photo Credit: Wisconsin DNR

By Linda Williams, DNR Forest Health specialist, Woodruff
Linda.Williams@wisconsin.gov or 920-360-0665

Northern pitch twig moth (Petrova alhicapitana) is also called the pitch nodule maker or pitch blister moth.

It feeds on branches and twigs of young jack pine and scotch pine, causing a hollow blister of gooey pitch to form around the larvae as it feeds at the base of a lateral branch. It prefers trees that are 20 feet tall or smaller, although it can attack older trees.

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Native Sawyer Beetles Resemble Asian Longhorned Beetle

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An adult Asian longhorned beetle, left, and an adult whitespotted sawyer beetle, right. The arrow shows the white spot at the top of the whitespotted sawyer beetle’s wing covers, indicating it’s the native beetle and not Asian longhorned beetle. / Photo Credits: Left, Bugwood.org; right, Wisconsin DNR

Two closeup photos show the similarities and differences between an adult Asian longhorned beetle, left, with spots all over its back and striped antennae; and an adult whitespotted sawyer beetle, right, with one white spot beneath its head and between its wings.

By Michael Hillstrom, DNR Invasive Forest Pest Coordinator
Michael.Hillstrom@wisconsin.gov

More than 300 species of longhorn beetles inhabit the Midwest. The Wisconsin Department of Natural Resources (DNR) posted about one species, the invasive Asian longhorned beetle (ALB), on social media in early July.

Forest Health staff received many photos of potential ALB as a result. Fortunately, none of the photos were of ALB – which has yet to be detected in Wisconsin.

By far, the most common insect seen in the submitted photographs was a native longhorn species called the whitespotted sawyer beetle (Monochamus scutellatus), also known as a pine sawyer beetle.

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Herbicide Damage To Trees? Always Read The Label

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Closeup photo showing active ingredients listed on the front label of pesticide containers. The complete label, including instructions, may be on the front or back of the bottle and will require opening to read.

Active ingredients are listed on the front of pesticide containers (yellow arrow above). The complete label, including instructions, may be on the front or back of the bottle and will require opening to read (blue arrow above). / Photo Credit: Wisconsin DNR

By Linda Williams, DNR Forest Health Specialist
Linda.Williams@wisconsin.gov or 920-360-0665

This is your reminder to always read pesticide labels, even if you think the product you are using is the same product you’ve always used.

Do you always check the active ingredients listed on the front of pesticide containers – and read instructions on the use of the product – every time you buy a new container of pesticide? It has become more important than ever to do so.

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Japanese Beetle Defoliates Some Forest Trees In The North

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Closeup photo of Japanese beetles defoliating a basswood leaf

Japanese beetles defoliating a basswood leaf. / Photo Credit: Wisconsin DNR

By Linda Williams, DNR Forest Health Specialist
Linda.Williams@wisconsin.gov or 920-360-0665

The Japanese beetle (Popillia japonica) is an invasive insect that feeds on many plant species. The adult beetles “skeletonize” leaves by eating the material between the veins.

Adult Japanese beetles feed on the flowers and leaves of more than 300 plant species, including trees, shrubs and herbaceous plants. Forest trees can be defoliated, with open-grown or edge trees suffering the highest defoliation rates.

Japanese beetles favor birch, mountain ash and basswood (linden) trees, but they have also been observed feeding on the leaves of young oaks.

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Viburnum Leaf Beetle Appearing In Forests

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By Linda Williams, DNR Forest Health Specialist
Linda.Williams@wisconsin.gov or 920-360-0665 

Closeup photo showing small brown adult viburnum leaf beetles causing typical defoliation on a leaf.

Small brown adult viburnum leaf beetles cause typical defoliation on a leaf. / Photo Credit: Wisconsin DNR

Viburnum leaf beetle (Pyrrhalta viburni) is a relatively new invasive insect in Wisconsin. It originated in Eurasia and was first identified in Wisconsin in 2009.

Adults and larvae feed on the leaves of viburnums and can cause mortality after a few years of repeated defoliation. Feeding causes characteristic holes in the leaves. Beetle numbers can be very high on a single plant.

Viburnum leaf beetle has been observed defoliating native viburnum species including American Highbush Cranberry (Viburnum opulus var. americana) and Mapleleaf Viburnum (Viburnum acerifolium) in forest stands in Iron County and more recently in Oneida County.

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Locust Sawfly Defoliation Found In Oneida County

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By Linda Williams, DNR Forest Health Specialist
Linda.Williams@wisconsin.gov or 920-360-0665

Closeup photo showing four locust sawfly larvae feeding on bristly locust leaves.

Four locust sawfly larvae feed on bristly locust leaves. / Photo credit: Wisconsin DNR

In early July, black locust and bristly locust in several areas of Oneida County were severely defoliated by locust sawfly.

Affected trees and shrubs have now produced additional leaves, making the defoliation less obvious. Damage was not noted in other areas of the state.

The sawflies are finished feeding, so no control is necessary.

Forest Health Specialists Plan Public Talks

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By Art Kabelowsky, DNR Outreach and Communications
Arthur.Kabelowsky@wisconsin.gov or 608-335-0167

Photo showing Wisconsin Department of Natural Resources Forest Health specialists (from left) Bill McNee, Paul Cigan and Linda Williams discuss a tree during the Cambridge Tree Tour in July 2025.

Wisconsin Department of Natural Resources Forest Health specialists (from left) Bill McNee, Paul Cigan and Linda Williams discuss a tree during the Cambridge Tree Tour in July 2025. / Photo Credit: Wisconsin DNR

Two Wisconsin Department of Natural Resources (DNR) Forest Health specialists will give presentations that are open to the public in the coming weeks:

  • Thursday, Aug. 7: Alex Hornung, Wisconsin DNR Forest Health specialist for central Wisconsin, will discuss the DNR’s Forestry program at Farm Technology Days. The event will run from noon to 5 p.m. at Clinton Farms, E8351 State Hwy 22, Bear Creek (Waupaca County). Admission is $15 per adult.
  • Friday, Sept. 5: Paul Cigan, DNR Forest Health specialist for northwest Wisconsin, will give a presentation on “Fungal Pathogens of the Wisconsin Forest” as part of the Wisconsin Mycological Society’s “Northwoods Foray” in Cable (Bayfield County). Cigan’s talk will run from 7:30 to 8:30 p.m. The Northwoods Foray will run from Sept. 4-7. Those interested in attending can visit the event’s webpage to obtain more information and sign up for a fee.

Armillaria Root Disease: A Fungal Killer

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A photo showing that after bark has been removed from a declining white spruce, the white mycelial mat of Armillaria can be seen under the bark.

Bark has been removed from a declining white spruce to show the white mycelial mat of Armillaria under the bark. / Photo Credit: Linda Williams, Wisconsin DNR

By Linda Williams, DNR Forest Health Specialist
Linda.Williams@wisconsin.gov or 920-360-0665

Armillaria is a root-rot pathogen that usually lives quietly under the soil. But when trees experience stress, the fungus can attack and colonize the roots of the stressed tree.

Armillaria can infect many different species of trees, and trees of any age or size, but the result for the tree is usually a slow decline and eventual death. Stressors can include drought and flooding, defoliation from insects or diseases or physical damage such as when roots are severed.

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