Caterpillars
Trembling aspen trees in rural Strathcona County have been attacked by a number of different caterpillars this spring. The majority of concerns have been isolated to central Strathcona County.
Because the defoliation occurred early in the season the trees will have a reflush of leaves.
Caterpillars attacking Trembling Aspen trees in Strathcona County
Causes
The main pests responsible are:
| Linden Looper |
|
|
- Linden loopers are dull-to-brightly yellow-sided
- feed on a variety of hardwoods including poplar, birch and maples
- start feeding early in May and pupate by the middle of June
- drop to lower branches by silken threads
- outbreaks generally last 1 ? 2 years
- adults emerge in the fall, the females do not fly
- they crawl up the tree trunk to mate and lay their egg
- overwinter in the egg stage
- a sticky product such as Tanglefoot placed around the base of the tree would stop the females from getting up the tree
|
| Large Aspen Tortrix |
 |
- mature larva is green to black with a black head and anal plate
- major defoliator of trembling aspen but also feeds on balsam poplar, willow and birch
- larva start feeding in early May just before the buds break
- larva will roll leaves or pull several leaves together and secure with a silken thread
- pupation occurs by mid June
- adults emerge at the end of June to mid July
- the eggs are laid on the surface of the leaf and hatch by the end of July
- the larva pulls leaves together and feeds on the surface of the leaf until mid August
- damage is insignificant at this stage
- overwinter as a larva under bark scales
- outbreaks are 2 ? 3 years in duration
|
| Speckled Green Fruit Worm |
|
|
- greyish to green in colour with several narrow white stripes along the top and sides
- eggs are laid on twigs and trees
- overwinter as pupae in the soil
- major defoliator of trembling aspen and willow
|
| Bruce Spanworm |
 |
- Bruce spanworm larvae are variable in color, ranging from vivid green to dark brown, with three thin yellow lines on each side of the body
- trembling aspen is the primary food source but they will feed on willows, balsam poplar, Manitoba maple, chokecherry, saskatoons, currants and wild roses
- start feeding early in May and pupate by the middle of June
- drop to lower branches by silken threads
- often occur with outbreaks of other defoliators
- outbreaks generally last 2 years
- adults emerge in the fall, the females do not fly
- they crawl up the tree trunk to mate and lay their eggs
- overwinter in the egg stage
- a sticky product such as Tanglefoot placed around the base of the tree would stop the females from getting up the tree
|
| Forest Tent Caterpillar |
 |
- Forest tent caterpillars have blue stripes and white keyhole shapes down their backs
- overwinter in the egg stage
- hatching occurs in the spring about the time the tree buds begin to swell
- feeds on a wide variety of hardwoods; trembling aspen is preferred
- eggs are laid in masses in a ring around the branch containing 100 to 350 eggs
- one generation per year
|
|
Control
- one insecticide that can be used on the caterpillars is Bacillus thuringienisis (Bt) (it would need to be applied in May while the larva are still small)
- any registered contact insecticide, like Malathion, can be used to help control these caterpillars on ornamental trees
- Control of these caterpillars is usually not necessary due to the short duration of the outbreaks since there are a number of natural predators that keep the numbers in check
|
| Natural predator |
 |
- A large species of Ground Beetle is also present, commonly called the Fiery Hunter, that is feeding on the caterpillars.
- Avoid insecticides as they may harm these beneficial beetles.
|
Results
The numbers of these pests won't stay high for more than a year or two before dropping to normal levels, with the exception of the Forest Tent Caterpillar that can have high numbers for three to six years. The caterpillars will be pupating within the next two weeks allowing the trees to reflush in July; although, the leaves will be smaller and there will be fewer leaves than normal.
| Linden Looper |
|
|
- Linden loopers are dull-to-brightly yellow-sided
- feed on a variety of hardwoods including poplar, birch and maples
- start feeding early in May and pupate by the middle of June
- drop to lower branches by silken threads
- outbreaks generally last 1 ? 2 years
- adults emerge in the fall, the females do not fly
- they crawl up the tree trunk to mate and lay their egg
- overwinter in the egg stage
- a sticky product such as Tanglefoot placed around the base of the tree would stop the females from getting up the tree
|
| Large Aspen Tortrix |
|
- mature larva is green to black with a black head and anal plate
- major defoliator of trembling aspen but also feeds on balsam poplar, willow and birch
- larva start feeding in early May just before the buds break
- larva will roll leaves or pull several leaves together and secure with a silken thread
- pupation occurs by mid June
- adults emerge at the end of June to mid July
- the eggs are laid on the surface of the leaf and hatch by the end of July
- the larva pulls leaves together and feeds on the surface of the leaf until mid August
- damage is insignificant at this stage
- overwinter as a larva under bark scales
- outbreaks are 2 ? 3 years in duration
|
| Speckled Green Fruit Worm |
|
|
- greyish to green in colour with several narrow white stripes along the top and sides
- eggs are laid on twigs and trees
- overwinter as pupae in the soil
- major defoliator of trembling aspen and willow
|
| Bruce Spanworm |
|
- Bruce spanworm larvae are variable in color, ranging from vivid green to dark brown, with three thin yellow lines on each side of the body
- trembling aspen is the primary food source but they will feed on willows, balsam poplar, Manitoba maple, chokecherry, saskatoons, currants and wild roses
- start feeding early in May and pupate by the middle of June
- drop to lower branches by silken threads
- often occur with outbreaks of other defoliators
- outbreaks generally last 2 years
- adults emerge in the fall, the females do not fly
- they crawl up the tree trunk to mate and lay their eggs
- overwinter in the egg stage
- a sticky product such as Tanglefoot placed around the base of the tree would stop the females from getting up the tree
|
| Forest Tent Caterpillar |
|
- Forest tent caterpillars have blue stripes and white keyhole shapes down their backs
- overwinter in the egg stage
- hatching occurs in the spring about the time the tree buds begin to swell
- feeds on a wide variety of hardwoods; trembling aspen is preferred
- eggs are laid in masses in a ring around the branch containing 100 to 350 eggs
- one generation per year
|
|
Control
- one insecticide that can be used on the caterpillars is Bacillus thuringienisis (Bt) (it would need to be applied in May while the larva are still small)
- any registered contact insecticide, like Malathion, can be used to help control these caterpillars on ornamental trees
- Control of these caterpillars is usually not necessary due to the short duration of the outbreaks since there are a number of natural predators that keep the numbers in check
|
| Natural predator |
|
A large species of Ground Beetle is also present, commonly called the Fiery Hunter, that is feeding on the caterpillars. |
Last updated: Tuesday, May 17, 2011
Page ID: 3490
