invasive insects

Cook Forest, and much of Northwest Pennsylvania, is beset by a number of invasive insects that are causing widespread tree mortality. Those destructive, non-native insects listed and linked below are presently of the greatest concern.  In Cook Forest State Park and surrounding areas, Hemlock Woolly Adelgid (HWA) is a monumental threat – due not only to the density of eastern Hemlock and its keystone importance to our forests and our clean waters, but also because these hemlocks comprise a large percentage of the best remaining old-growth stands in the eastern US.  

While scientists work on combating these destroyers of biodiversity – by identifying and releasing biologic controls (i.e., bugs and creatures that predate on these invasive insects), and by studying pesticide options – but everyone can help limit the damage, in a number of ways. 

HWA infestation - hemlock woolly adelgid invasive insect
HWA on a hemlock - Chris Evans, University of Illinois,

What we can do - as landowners:

In addition to attending our annual HWA seminars, and talking to their county Service Forester (it’s free!) about any suspected forestry issues, landowners can:

  • inspect their property at regular intervals, noting and reporting any appearance of or infestation by any of the following insects;
  • Coordinate similar efforts with owners of the adjacent properties, as any action (or inaction) on neighboring parcels will impact one another;
  • and consider employing biologic or pesticide controls, selective thinning of affected stands, and re-planting of native or resistant species or cultivars.
Contact the CFC with questions, and we’ll help or find someone who can. 

Visiting responsibly - protect Cook Forest on your vacation:

Burn it or Leave it – by state regulation, it’s prohibited to transport firewood from one area to another, as this is a primary way that invasive insects spread.

Report Suspected Insect Infestations – Visitors can also help by reporting any evidence of infestation they spot during hikes to the park office, or by emailing the PA Bureau of Forestry at  

Keep the Trees Healthy – Never make holes in trees (by nailing posters, or for hanging camp equipment), or damage bark (by carving or by hanging hammocks without tree-friendly straps), as either will weaken the tree and allow easier access for insects and disease.  Root damage and soil compaction make it harder for stressed trees to survive hotter summers and drought periods, so please don’t park on roots, or hike off-trail.

invasive insect damage - HWA - hemlock woolly adelgid
Hemlock death due to HWA infestation - image courtesy USDA Forest Service Southern Research Station , USDA Forest Service, SRS,

Help us track them

Report any sightings (especially with GPS-tagged photos) of any of the above to: 

The National Phenology Network publishes infestation forecast maps for the best times to inspect and to treat for various invasives, including the HWA — view its current map here.

Help us stop them - Cook Forest vs. Invasive Insects

Each year, the Bureau of Forestry has conducted HWA seminars arranged by the CFC for landowners, explaining why it’s important to keep their hemlocks healthy, and empowering them to do so.  (photo below!)

The CFC also works with the local DCNR offices, Penn State Extension, and the Allegheny Forest Health Collaborative on citizen scientist training, infestation monitoring, and tree treatment.  You can help protect the forest by helping us: 

2019-09-14 CFC BOF HWA Seminar Cook Forest
PA Bureau of Forestry scientists demonstrating an injection technique to kill hemlock woolly adelgid, while protecting park trees

Insects of Greatest Concern

Hemlock Woolly Adelgid — the HWA has killed millions of Eastern (a/k/a Canadian) Hemlock, Pennsylvania’s state tree, and an integral species for riparian health  — expanded information available from Penn State University.  Recovery of infected trees is possible, if infestation is detected early.

Emerald Ash Borer — 40 million trees dead to date, and rising.

Spotted Lanternfly — currently spreading west from southeast Pennsylvania, and especially deadly for fruit-bearing trees and vines.

Gypsy Moth — thee moths can kill many types of trees within a year of infestation, particularly oak.

Thousand Canker Disease — the combined activity of a fungus (Geosmithia morbida) and the walnut twig beetle kills black walnut trees within ten years, with no known cure (this link has additional information regarding firewood quarantines and associated penalties).

Asian Longhorned Beetle — ALB attacks hardwood trees, including Ash, Birch, Elm, Horse chestnut, Maple, and Popular, and it is currently impossible to save infested trees.  The ALB is known to be in New York and Ohio, and early detection is critical to containing it, as the devastation it would work unchecked is catastrophic.

EAB damage - Emerald Ash Borer invasive insect
Emerald Ash Borer damage