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Lilac borer (Ash borer)

  • Latin name: Podosesia syringae [Harr.]
  • French name: Sésie du lilas (ou Sésie du frêne)
  • Order: Lepidoptera
  • Family: Sesiidae


Canada, United States


Damage, symptoms and biology

The ash borer attacks young ash trees, both green and white, and common lilac, usually in the lower stem. Signs of ash borer activity include the following: holes in the bark with protruding sawdust and oozing sap, and in the spring, brown pupal cases at emergence holes. Larval tunnelling causes wilting of the foliage and stem breakage. Older, rough-barked stems are more susceptible to attack, especially those with wounds or graft scars.

In the southern and midwestern United States, the ash borer has a 1-year life cycle, but in thePrairie Provinces this species takes up to 3 years to complete development. Larvae pupate in feeding tunnels, just under the bark surface. Adult moth emergence occurs in June and early July. The adult ash borer is known as a clearwing moth because it lacks scales on its wings and therefore appears similar to a hornet or wasp.

The larvae dig into the bark and feed until the end of fall. They overwinter in the stem and begin to feed again in the spring before partially emerging as pupae in June.

After mating, each female lays up to 400 light brown, ovate eggs, usually in small clusters in bark crevices. Eggs hatch in 10-14 days. Larvae enter the sapwood and then tunnel upward to feed, forming larval galleries; when larvae are mature, they tunnel back towards the bark. Tunnels can be up to 32 cm long. Ash borer larvae have amber heads and thoracic shields, and white bodies, and are 26-34 mm in length when full-grown. Pupation lasts about 21 days and occurs in May of the final year of development.

Other information

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

Lilac borer (Ash borer)

Information on host(s)

Main host(s)

Ashes, common lilac, deciduous, green ash, lilac, mountain-ash, privet, white ash

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