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Cottonwood crown borer

  • Latin name: Sesia tibialis (Harris)
  • French name: Sésie du peuplier
  • Order: Lepidoptera
  • Family: Sesiidae




Damage, symptoms and biology

There is a great number of wood boring insects commonly found in live hardwoods in Canada. Most notable of these are the carpenterworm (Prionoxystus robiniae [Peck]), the poplar carpenterworm (Acossus centerensis [Lint.]), the aspen carpenterworm (A. populi [Wlk.]), the ash borer (Podosesia syringae [Harr.]), the cottonwood crown borer (Sesia tibialis [Harr.]), and the poplar-and-willow borer (Cryptorhynchus Iapathi [L.]). There are many other wood boring insects, most of which are bark beetles (Scolytidae), flatheaded wood borers (Buprestidae), and roundheaded or longhorned beetles (Cerambycidae). Most of the latter borers attack only dead or dying trees and are not usually a problem in living trees that are healthy.

The cottonwood crown borer is a pest of poplar and willow and commonly feeds in hybrid poplar stool beds.

These wood boring insects often go unnoticed in the trees they are attacking until severe damage has resulted. When attacked by one or more borer species, trees are usually weakened structurally and are susceptible to wind and snow breakage, especially if they are repeatedly attacked. Severe attack can place trees under stress, making them more susceptible to other damage agents such as drought and disease. If a tree is suspected of being attacked by a wood boring insect, careful examination will reveal small entry holes in the bark (often in and around old wounds) where the larvae of the developing moths or beetles extrude frass or debris. In many cases, small amounts of sap bleed from these entry holes. When a tree is severely attacked, large amounts of frass will accumulate at the base of the tree. Splitting the branches or stem of an attacked tree will reveal wood that is riddled with feeding tunnels. The cottonwood crown borer can be a serious pest of hybrid poplar stool beds, resulting in reduced production of poplar cuttings.

The cottonwood crown borer requires 2 years to complete its life cycle. Depending on their location, pupae move to the surface of either soil or bark before emerging as adult moths in late June or early July. These moths look like hornets with black and yellow-striped bodies and transparent wings. It is not known where eggs are laid on the host tree. Cottonwood crown borer larvae feed in tunnels in the cambial area (bark-wood interface) of both the lower stem and roots. Larvae have white bodies with dark red-brown heads and tan thoracic shields; when full-grown they are 40 mm in length. These borers overwinter twice in the larval stage because they require 2 years to complete their development. Pupation occurs in silk-lined, wood chip pupal chambers in the soil if larvae have fed in host tree roots; larvae pupate just below the bark surface if they have fed in the stem. Pupation length is unknown but is probably around 20 days.

Other information

A number of biotic agents act as natural controls for wood borers of hardwoods. Studies have shown that birds, particularly woodpeckers, may feed on up to 75% of a population of wood borers and are probably the most effective natural control agent. Parasitic insects, especially parasitic wasps, also feed on wood borers. In the United States, fast-growing wood decay fungi have been documented as trapping pupae within feeding tunnels, thus preventing adult emergence.

Most of the wood borers prefer wounds and scars on trees for oviposition. Care should therefore be taken when working on or near ornamental hardwoods, because careless cultivation, pruning, or mowing may cause injury resulting in oviposition sites. Ornamental trees that are healthy and growing well are most resistant to wood borer attacks. During drought, trees should be watered to prevent the drought stress that may predispose trees to wood borer attacks.

If a high-value ornamental tree has been attacked by only a few larvae, these larvae may be killed by inserting a flexible, small gauge wire into the entry holes. When the wire is fully inserted, it may puncture and kill the burrowing larva. Several attempts may be necessary to be successful. When trees have been severely attacked (i.e., brood trees), they should be removed and destroyed before neighbouring trees can be attacked by subsequent generations emerging from the brood trees.

To prevent adult moths from emerging, some infested trees can be tightly wrapped in burlap, which will trap moths in the feeding tunnels. This method is only used on small trees, where all emergence holes can be covered. Wrapping large trees is impractical because some emergence holes may be located on larger, inaccessible branches.

Pheromones are commercially available for the ash borer and can be used to trap moths around ornamental hardwoods to interrupt mating and prevent oviposition. Research on the carpenterworm and the cottonwood crown borer has isolated the pheromones released by female moths of these species to attract male moths. These pheromones are not commercially available in Canada but may be obtained through suppliers in the United States.

Canadian Forest Service Publications

Cottonwood crown borer

Diet and feeding behaviour

  • Saproxylophagous : Develops in partially decomposed woody debris.
    • Borer: Bores into and feeds on the woody and non-woody portions of plants.
Information on host(s)

The carpenterworm primarily attacks poplar and green ash in the prairie provinces, but it is known to attack a variety of hardwoods elsewhere on the continent. Poplar and aspen carpenterworms attack poplar and aspen, respectively.

Main host(s)

, balsam poplar, black cottonwood, Carolina poplar, common lilac, eastern cottonwood, European black poplar, European white poplar, green ash, hybrid poplar, Jack’s hybrid poplar, lanceleaf cottonwood, largetooth aspen, Lombardy poplar, narrowleaf cottonwood, plains cottonwood, plains cottonwood, poplars / aspens / cottonwoods, trembling aspen

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