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Aspen carpenterworm

  • Latin name: Acossus populi (Walker)
  • French name: Charpentier du tremble
  • Order: Lepidoptera
  • Family: Cossidae



Known to occur in Nevada, Colorado, California, and in the northern Rocky Mountains, but reportedly found from coast to coast and in Ontario and British Columbia in southern Canada.


Trunk, Bark

Damage, symptoms and biology

There are a number of wood boring insects commonly found in live hardwoods of the Prairie Provinces. These wood boring insects often go unnoticed in the trees they are attacking until severe damage has resulted. When attacked by one or more of these 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. .

Little information exists on the life cycles of poplar and aspen carpenterworms, but they are probably similar to each other. The poplar carpenterworm pupates within its host tree, with adult moths emerging in June and July. These adults have wingspans of 40-50 mm, while the wingspans of aspen carpenterworm adult moths are slightly larger at 50-60 mm. Adults of both these species are similar in appearance to the adult carpenterworm, with mottled gray wings and bodies. The larvae of these Acossus species have off-white bodies with brown spots and dark brown heads and thoracic shields. Life cycle duration of both species is unknown.

Adult: Rather stoutbodied, whitish ash gray moth with yellowish gray and black markings. Forewing very light gray with an irregular network of black reticulations heavier and more distinct in wing centre. Wingspan of 60 to 80 mm. Antennae and labial palpi black, and head gray with yellowish gray collar. Thorax gray with incomplete dark collar anteriorly and two transverse black marks posteriorly. Gray abdomen. Females distinguishable from males by their slightly heavier bodies, lighter gray colour, less distinct reticulation on hindwings, and threadlike antennae (male antennae are feathery).

Larva : Cream coloured, shiny, and hairless with dark brown head and thoracic shield, and 35 to 40 mm long.

Adults emerge in July and deposit their eggs in bark crevices of host trees. Young larvae tunnel under the bark initially, then produce extensive galleries in the wood. Little is known of their life cycle; hosts and geographical range are similar to those of A. centerensis, and habits and development are probably similar also.

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.

Canadian Forest Service Publications

Aspen carpenterworm

Information on host(s)

Cottonwoods and poplars listed as general hosts; quaking aspen mentioned as a specific hosts.

Main host(s)

, balsam poplar, black cottonwood, Carolina poplar, eastern cottonwood, European black poplar, European white poplar, 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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