Top Invasive Forest Insects in Ontario:
1. Emerald Ash Borer (Agrilus planipennis)
Hosts: Ash species
Signs: D-shaped exit holes, crown dieback
Impact: Rapid tree death, widespread ash loss
Management: Insecticide injections, removal of infested trees, ash wood quarantine, plant alternative species
2. Gypsy Moth (Lymantria dispar)
Hosts: Oaks, birch, poplar
Signs: Hairy caterpillars, defoliation
Impact: Severe canopy loss, tree stress, mortality in repeated outbreaks
Management: BtK spraying, egg mass scraping, burlap bands, pheromone traps
3. Hemlock Woolly Adelgid (Adelges tsugae)
Hosts: Eastern Hemlock
Signs: White woolly sacs under needles, needle loss
Impact: Needle drop, tree death within 4–10 years
Management: Imidacloprid soil drench, removal of infested material, early detection
4. Asian Longhorned Beetle (Anoplophora glabripennis)
Hosts: Maple, birch, willow, poplar
Signs: Round exit holes, larval galleries
Impact: Hardwood mortality, potential forest disruption
Management: Remove and destroy infested trees, surveillance, movement restrictions
5. Bronze Birch Borer (Agrilus anxius)
Hosts: Birch species
Signs: D-shaped exit holes, bark splitting, canopy thinning
Impact: Kills stressed trees quickly
Management: Monitor, insecticide treatments, remove weakened trees
6. Larch Casebearer (Coleophora laricella)
Hosts: Tamarack / Larch
Signs: Larvae in silken needle cases, defoliation
Impact: Weakens trees, reduced growth
Management: Insecticide application, biological control, monitoring
7. Spotted Lanternfly (Lycorma delicatula)
Hosts: Maples, fruit trees, grapes
Signs: Winged adults with black spots, honeydew, sooty mold
Impact: Tree stress, economic loss
Management: Quarantine, sticky traps, remove egg masses, insecticides
8. Dogwood Borer (Synanthedon scitula)
Hosts: Dogwoods
Signs: Sawdust at branch bases, branch dieback
Impact: Can kill stressed trees
Management: Prune and destroy infested branches, insecticide treatment
9. Black Pine Bast Scale (Matsucoccus matsumurae)
Hosts: Pine species
Signs: Cottony masses on bark, needle drop
Impact: Reduced growth, may kill trees
Management: Insecticide sprays, biological control, monitoring
10. Alder Leaf Beetle (Agelastica alni)
Hosts: Alders
Signs: Shiny blue-black beetles, skeletonized leaves
Impact: Defoliation, tree stress
Management: Hand-pick beetles, insecticide if severe, monitoring
11. European Gypsy Moth (Lymantria dispar dispar)
Hosts: Oaks, maples, aspens
Signs: Hairy caterpillars, defoliation
Impact: Weakens trees, repeated outbreaks can kill
Management: See Gypsy Moth (#2)
12. Hemlock Borer (Melanophila picta)
Hosts: Eastern Hemlock
Signs: Small exit holes, larval galleries
Impact: Weakens trees, can kill stressed trees
Management: Monitor, remove infested trees, insecticides for high-value trees
13. Eastern Tent Caterpillar (Malacosoma americanum)
Hosts: Cherry, apple
Signs: Silken tents in branch forks, defoliation
Impact: Usually temporary stress; repeated infestations weaken trees
Management: Remove tents, pruning, BtK application
14. Chestnut Gall Wasp (Dryocosmus kuriphilus)
Hosts: Chestnut species
Signs: Small galls on leaves/branches
Impact: Reduces growth, lowers nut production
Management: Biological control, monitor gall formation, prune infested shoots
15. Willow Leaf Beetle (Chrysomela aeneicollis)
Hosts: Willow species
Signs: Metallic green beetles, skeletonized leaves
Impact: Defoliation, tree stress
Management: Insecticides, monitor, remove heavily infested leaves
16. Rusty Willow Beetle (Plagiodera versicolora)
Hosts: Willows
Signs: Brown beetles, leaf skeletonization
Impact: Weakens trees
Management: Insecticide, monitoring
17. Asian Woolly Hackberry Aphid (Shivaphis celti)
Hosts: Hackberry
Signs: White woolly covering, leaf curling
Impact: Stress, reduced growth
Management: Prune infested branches, insecticidal soap, monitor
18. Black Locust Tree Scale (Chionaspis pinifoliae)
Hosts: Black Locust
Signs: White scales along branches
Impact: Weakens trees, dieback
Management: Horticultural oil, pruning, monitor
19. Buckthorn Leaf Beetle (Galerucella calmariensis)
Hosts: Buckthorn
Signs: Leaf defoliation
Impact: Reduces buckthorn vigor; sometimes used as biocontrol
Management: None needed; may act as biocontrol
20. Emerald Ash Borer Predators (Tetrastichus planipennisi, Spathius agrili)
Hosts: Ash
Signs: Parasitoid wasps attack EAB larvae
Impact: Biological control agent, reduces EAB populations
Management: Release programs in infested areas
21. European Elm Scale (Gossyparia spuria)
Hosts: American & Slippery Elm
Signs: White scale on bark, yellowing leaves
Impact: Weakens trees, encourages fungal infections
Management: Monitor, horticultural oil application, pruning
22. Maple Leaf Cutter (Paraclemensia acerifoliella)
Hosts: Maples
Signs: Small leaf cuts, rolled edges, defoliation
Impact: Minor defoliation; repeated outbreaks weaken young trees
Management: Prune affected leaves, monitor populations
23. Elm Leaf Beetle (Xanthogaleruca luteola)
Hosts: Elm species
Signs: Skeletonized leaves, yellowing
Impact: Defoliation, stress on trees, reduced growth
Management: Insecticide treatments, remove fallen leaves, biological control
24. Sycamore Lace Bug (Corythucha ciliata)
Hosts: Sycamore, plane trees
Signs: Yellow stippling on leaves, black frass
Impact: Reduced photosynthesis, leaf drop in severe infestations
Management: Monitor, insecticidal soap, promote natural predators
25. European Pine Sawfly (Neodiprion sertifer)
Hosts: Pines
Signs: Larvae feeding on needles, defoliation
Impact: Weakens trees, reduces growth
Management: Hand-pick larvae, insecticides, encourage predators
26. White Pine Weevil (Pissodes strobi)
Hosts: Eastern White Pine, other pines
Signs: Terminal leader dieback, resin exudation
Impact: Deforms trees, reduces timber quality
Management: Prune damaged leaders, insecticides for high-value trees
27. Pine Shoot Beetle (Tomicus piniperda)
Hosts: Pines
Signs: Shoot dieback, resin at entrance holes
Impact: Weakens trees, reduces growth
Management: Remove infested material, monitor, insecticides if necessary
28. Hemlock Looper (Lambdina fiscellaria)
Hosts: Hemlock, other conifers
Signs: Caterpillars defoliating needles
Impact: Can cause temporary defoliation; repeated outbreaks stress trees
Management: BtK applications, remove heavily infested branches
29. Spruce Budworm (Choristoneura fumiferana)
Hosts: Spruce, fir
Signs: Feeding on new buds, brown needles
Impact: Defoliation, reduced growth, tree mortality in repeated outbreaks
Management: BtK sprays, pheromone traps, monitor populations
30. Larch Sawfly (Pristiphora erichsonii)
Hosts: Tamarack / Larch
Signs: Larvae feeding on needles, yellowing
Impact: Weakens trees, reduces growth
Management: Hand-pick larvae, insecticides, monitoring
31. Elm Bark Beetle (Scolytus multistriatus / Hylurgopinus rufipes)
Hosts: Elm species
Signs: Small exit holes, tunneling under bark
Impact: Vector for Dutch Elm Disease, kills trees
Management: Monitor, remove infected trees, control vector insects
32. Oak Leaf Roller (Archips semiferanus)
Hosts: Oaks
Signs: Rolled leaves, feeding caterpillars
Impact: Minor to moderate defoliation, weakens young trees
Management: Prune rolled leaves, monitor, BtK treatment
33. Birch Leafminer (Fenusa pusilla)
Hosts: Birch species
Signs: Mines in leaves, brown blotches
Impact: Defoliation, reduces vigor
Management: Monitor, insecticide if severe, promote parasitoids
34. Hemlock Looper (Nepytia janetae)
Hosts: Eastern Hemlock
Signs: Caterpillars defoliating needles
Impact: Defoliation, tree stress
Management: Monitor, BtK, encourage predators
35. Spruce Gall Adelgid (Adelges spp.)
Hosts: Spruce species
Signs: Galls on needles or buds
Impact: Reduces growth, deformity
Management: Prune galls, insecticides, monitor
36. European Pine Sawfly (Diprion pini)
Hosts: Pines
Signs: Caterpillars feeding on needles, defoliation
Impact: Weakens trees, reduces growth
Management: Hand-pick larvae, insecticides, monitoring
37. Larch Casebearer (Coleophora laricella)
Hosts: Tamarack / Larch
Signs: Silken needle cases, defoliation
Impact: Weakens trees, reduces growth
Management: Insecticide, biological control, monitoring
38. Pine Needle Scale (Chionaspis pinifoliae)
Hosts: Pines
Signs: White scales on needles, yellowing
Impact: Weakens trees, reduces growth
Management: Horticultural oils, monitoring, prune infested branches
39. European Spruce Beetle (Ips typographus)
Hosts: Spruce species
Signs: Small round exit holes, galleries under bark
Impact: Can kill stressed trees, reduces growth
Management: Remove infested trees, pheromone traps, monitor
40. Birch Bark Beetle (Scolytus ratzeburgi)
Hosts: Birch species
Signs: Tiny round exit holes, bark galleries
Impact: Weakens or kills stressed trees
Management: Remove infested material, monitor, insecticides if needed
41. Dogwood Borer (Synanthedon scitula)
Hosts: Dogwoods
Signs: Sawdust at branch bases, branch dieback
Impact: Can kill stressed trees
Management: Prune and destroy infested branches, insecticide treatment
42. Asian Woolly Hackberry Aphid (Shivaphis celti)
Hosts: Hackberry
Signs: White woolly covering, leaf curling
Impact: Stress, reduced growth
Management: Prune infested branches, insecticidal soap, monitor
43. Black Locust Tree Scale (Chionaspis pinifoliae)
Hosts: Black Locust
Signs: White scales along branches
Impact: Weakens trees, dieback
Management: Horticultural oil, pruning, monitor
44. European Elm Bark Beetle (Scolytus multistriatus / Hylurgopinus rufipes)
Hosts: Elm species
Signs: Small exit holes, tunneling under bark
Impact: Vector for Dutch Elm Disease, kills trees
Management: Monitor, remove infected trees, control vector insects
45. Spruce Budworm (Choristoneura fumiferana)
Hosts: Spruce, fir
Signs: Feeding on new buds, brown needles
Impact: Defoliation, reduced growth, mortality in repeated outbreaks
Management: BtK sprays, pheromone traps, monitor populations
46. Hemlock Woolly Adelgid (Adelges tsugae)
Hosts: Eastern Hemlock
Signs: White woolly sacs under needles, needle loss
Impact: Needle drop, tree death within 4–10 years
Management: Imidacloprid soil drench, removal of infested material, early detection
47. European Pine Sawfly (Neodiprion sertifer)
Hosts: Pines
Signs: Larvae feeding on needles, defoliation
Impact: Weakens trees, reduces growth
Management: Hand-pick larvae, insecticides, encourage predators
48. Larch Casebearer (Coleophora laricella)
Hosts: Tamarack / Larch
Signs: Larvae in silken needle cases, defoliation
Impact: Weakens trees, reduced growth
Management: Insecticide application, biological control, monitoring
49. Birch Leafminer (Fenusa pusilla)
Hosts: Birch species
Signs: Mines in leaves, brown blotches
Impact: Defoliation, reduces vigor
Management: Monitor, insecticide if severe, promote parasitoids
50. Eastern Tent Caterpillar (Malacosoma americanum)
Hosts: Cherry, apple
Signs: Silken tents in branch forks, defoliation
Impact: Temporary stress; repeated infestations weaken trees
Management: Remove tents, pruning, BtK application
51. Hemlock Looper (Lambdina fiscellaria)
Hosts: Hemlock, other conifers
Signs: Caterpillars defoliating needles
Impact: Can cause defoliation; repeated outbreaks stress trees
Management: BtK applications, remove heavily infested branches, monitor
52. Spruce Gall Adelgid (Adelges spp.)
Hosts: Spruce species
Signs: Galls on needles or buds
Impact: Reduces growth, deformity
Management: Prune galls, insecticides, monitor
53. European Spruce Beetle (Ips typographus)
Hosts: Spruce species
Signs: Small round exit holes, galleries under bark
Impact: Can kill stressed trees, reduces growth
Management: Remove infested trees, pheromone traps, monitor
54. Pine Needle Scale (Chionaspis pinifoliae)
Hosts: Pines
Signs: White scales on needles, yellowing
Impact: Weakens trees, reduces growth
Management: Horticultural oils, monitoring, prune infested branches
55. Birch Bark Beetle (Scolytus ratzeburgi)
Hosts: Birch species
Signs: Tiny round exit holes, bark galleries
Impact: Weakens or kills stressed trees
Management: Remove infested material, monitor, insecticides if needed