Climate Impacts On Forest Insects

Climate change may impact forest insects in a variety of ways that will likely put stress on the forest. Warmer temperatures, altered precipitation patterns, more frequent extreme weather events and longer growing seasons are a few consequences of climate change that may shape the effects of insects in future forests. A changing climate may impact insects as:

  • Warmer temperatures accelerate larval development and increase insect populations.
  • Extended growing seasons allow for more generations of insects each year.
  • Altered leaf chemistry modifies insect host plant preferences.
  • Extreme weather events damage and stress forests, resulting in attacks by native and non-native insects.
  • Warmer temperatures allow insects to expand their range and occupy new areas.

Many examples of insects responding to climate change have already been documented. Two examples are:

1) Mountain pine beetle expanding its geographic range in the western U.S. and infesting a new host tree species during the most recent outbreak; and

2) Eastern larch beetle having an additional generation each year that has resulted in an unprecedented 20-year outbreak in Minnesota. Continue reading “Climate Impacts On Forest Insects”

Forest Health In The Statewide Forest Action Plan

The forest health chapter of Wisconsin’s 2020-2030 Statewide Forest Action Plan, completed in June 2020, highlights the impacts of insects, diseases, invasive plants and worms in Wisconsin’s forests.

Forest health experts from government agencies, universities and tribes worked together to evaluate these current impacts. They then developed goals and strategies to help the forestry community refine how it will invest state, federal and partner resources to address major forest health management and landscape priorities over the next ten years.

Forest health is a critical component of the plan because native and non-native pests increase tree mortality to a level that negatively affects forest stocking levels, clean water, wildlife habitat and raw material for wood products. This causes economic losses and undesirable management outcomes. Continue reading “Forest Health In The Statewide Forest Action Plan”

Planting and Seeding Trials In The Wake Of Ash Decline

Swamp White Oak seedling planted in a black ash replacement trial. Credit: Wisconsin DNR

The emerald ash borer (EAB) is causing widespread mortality of both upland and lowland ash. Black ash (and to a lesser extent green ash) is a forest wetland species that helps prevent sites from swamping through evapotranspiration. With the loss of ash in these systems, forest practitioners are developing silvicultural strategies to minimize the impacts through planting and seeding trials.

Acorn Weevils Make Acorns Float

Article By: Linda Williams, DNR Forest Health Specialist, Woodruff or 920-360-0665

Have you seen small round holes in acorns? These holes are a sign of acorn weevil damage that can occur in all Wisconsin oak species.

In a pile of brown and tan acorns, two have small round pencil-tip sized holes caused by acorn weevil larvae burrowing out from the inside.

Two acorns show exit holes of acorn weevils. / Photo Credit: Wisconsin DNR

Continue reading “Acorn Weevils Make Acorns Float”

Take Action! Look For Gypsy Moth Egg Masses

Article By:  Bill McNee, DNR Forest Health Specialist, Oshkosh or 920-360-0942

In 2021, gypsy moth populations increased for a second consecutive summer due to favorable weather conditions. Populations typically increase with an average or mild winter, below average spring precipitation and above average May through June temperatures.

Regional variation in weather can result in significant differences in populations. If weather conditions are favorable again in 2022, the most noticeable increase in caterpillar numbers would likely occur in southern counties, where conditions were driest during this past spring and summer.

Populations experience the fastest growth rate and are first noticed on:

  • Dry sites with sandy soil and abundant oak
  • Mowed lawns with preferred tree species (oak, crabapple, birch, etc.)
  • Large oaks (bur, in particular) with rough bark, especially on or adjacent to mowed lawns
Five small gypsy moth egg tan masses on a single tree branch in Walworth County.

Gypsy moth egg masses found in Walworth County in fall 2021.
Photo Credit: Gypsy moth egg masses KMSU













Continue reading “Take Action! Look For Gypsy Moth Egg Masses”

Managing Damage By White Pine Weevil

Article By:  Linda Williams, DNR Forest Health Specialist, Woodruff or 920-360-0665

Tree damage from white pine weevil is noticeable across Wisconsin this time of year. White pine weevils attack several different Wisconsin species, including eastern white pine, jack pine and spruce.

Adult weevils lay their eggs on terminal leaders in the spring. After the eggs hatch, larvae bore into the terminal and begin feeding downwards just under the bark which can result in the killing of a 1 to 2-feet section of the terminal leader as they feed. Terminal leaders will often have a wilted or “shepherds crook” appearance, and they will turn rusty red to brown late in the fall season. These dead terminal leaders will often break off during the winter.

A white pine tree with a cluster of dead twigs caused by a white pine weevil attack.

Dead terminal leader caused by a white pine weevil attack on a young white pine.
Photo Credit: Wisconsin DNR

Continue reading “Managing Damage By White Pine Weevil”

Mystery Walnut Defoliator Identified

Article by: Mike Hillstrom, Forest Health Specialist

In 2020, forest health staff in Wisconsin, Minnesota and Iowa received calls about black walnut stands being defoliated and webbed. In 2021, the defoliation expanded to multiple additional black walnut stands in southwest Wisconsin, while northeast Iowa and Minnesota continued to see damage. Recently, molecular work completed by the Wisconsin Department of Agriculture, Trade and Consumer Protection has identified the larvae causing the damage as a native Tortricid moth, Gretchena amatana.

G. amatana caterpillars on tree.

G. amatana caterpillars on tree.

Fine webbing covers walnut tree trunk.

Fine webbing covers walnut tree trunk.












Continue reading “Mystery Walnut Defoliator Identified”

Young Oaks Defoliated By Oak Slug Sawfly

Article By: Linda Williams, DNR Forest Health Specialist, Woodruff or 920-360-0665

The oak slug sawfly (Caliroa quercuscoccineae), sometimes called the scarlet oak sawfly, has the appearance of a small, slimy slug. Its slime helps it stick to leaves it feeds on. The oak slug sawfly’s tiny larvae feed in groups on the undersides of oak leaves, scraping out the green material from between the veins of the leaves. The upper leaf surface is usually left intact, creating a “stained glass window” look. Oak slug sawfly has the ability to completely defoliate leaves before dropping to the ground to pupate.

Two oak leaves eaten by oak slug sawfly larvae left with brown discoloration on the leaf and translucent patches.

Oak slug sawfly larvae cause defoliation on oak leaf after feeding.
Photo Credit: Wisconsin DNR

Continue reading “Young Oaks Defoliated By Oak Slug Sawfly”

Outdoor Hazards In Wisconsin: A Guide To Insects, Plants And Wildlife

Published by the University of Wisconsin-Madison Division of Extension, this guide will help you recognize, avoid and handle potential problems caused by wildlife, insects or plants.


  • Amphibians (salamanders, toads)
  • Reptiles (turtles, snakes)
  • Birds (defending territory, handling birds)
  • Mammals (short-tailed shrews, bats, skunks, porcupines, coyotes, gray wolves, deer, black bears)
  • Stinging insects (bees and wasps)
  • Blood-feeding insects (mosquitoes, deerflies and horseflies, blackflies, biting midges, ticks, chiggers)

Continue reading “Outdoor Hazards In Wisconsin: A Guide To Insects, Plants And Wildlife”

Diplodia Shoot Blight vs. Red Pine Shoot Moth

By Todd Lanigan, DNR Forest Health Specialist, Eau Claire, or 715-210-0150

Scattered damage to new red pine shoots has been observed across many counties this summer. With the intermittent rains during the summer, the first thought was that Diplodia shoot blight, a fungal disease, was causing the damage. Upon a closer look, some of the shoot mortality is caused by the red pine shoot moth. From a casual glance, these two problems will look the same, so you really need to take a closer look. 

If Diplodia causes the shoot mortality, the shoot usually forms a shepherd’s crook. And, in time, you will find the fungal fruiting bodies on the needles, especially if you look under the needle sheath (covering) at the base of the needles.

Shepherd’s crook caused by Diplodia shoot blight. Photo Credit: Elizabeth Bush, Virginia Polytechnic Institute and State University,

Continue reading “Diplodia Shoot Blight vs. Red Pine Shoot Moth”