Forest Pest Insects in North America: a Photographic Guide

Carpenterworm

Prionoxystus robiniae (Peck.) (Lepidoptera: Cossidae)

Orientation to pest

Carpenterworm, Prionoxystus robiniae (Peck.), is a native, wood-boring moth that attacks various hardwoods. Adults emerge between May and August and lay their eggs in large groups (200-1,000) on bark of hosts, often near wounds or objects on the bark such as vines or moss. Young larvae bore into the inner bark and feed there until half grown, at which time they bore into the sapwood and then the heartwood. In southern part of this species' range, immature stages may complete development in a single year, but in northern areas as many as 3 or 4 years may be required. Tunnels to the outside are kept open and enlarged as larvae grow. Tunnels are lined with silk by mature larvae and pupation occurs in the upper end of the tunnel near the exit hole. Pupae, when ready for adult emergence, wriggle to the exit where the adult emerges. The pupal case remains at the entrance of this exit hole. Carpenterworms seldom kill trees, but due to tunneling, infested trees are more likely to break in wind storms, may become more vulnerable to other pests, and the value of affected logs is reduced. No tree size preference has been noted for attack, with trees as small of 5 cm in diameter being infested. However, open grown trees, especially trees in urban landscapes and rural shelterbelts are at greatest risk of attack.

Hosts commonly attacked

In the southern United States, oaks (Quercus), particularly members of the red oak group, are heavily damaged. In the prairies and Rocky Mountains of North America, poplar species (Populus) and green ash (Fraxinus pennsylvanica Marshall) are major hosts. In California, live oak (Quercus agrifolia Née) and introduced elms (Ulmus) are hosts. Other hosts include black locust (Robinia pseudoacacia L.), maple (Acer), and willow (Salix), among others.

Distribution

This borer occurs in widely distributed in the United States and southern Canada.

Images of carpenterworm

Images of Species Number 366

Adults of the carpenterworm.  Female (left) and male (right) James Solomon, USDA Forest Service, Bugwood.org 768x512 / 1536x1024
Larvae of carpenterworm William H. Hoffard, USDA Forest Service, Bugwood.org 768x512 / 1536x1024

Larvae of carpenterworm James Solomon, USDA Forest Service, Bugwood.org 768x512 / 1536x1024
Larval gallery of carpenterworm James Solomon, USDA Forest Service, Bugwood.org 768x512 / 1536x1024
Surface injury from lateral gallery in trunk James Solomon, USDA Forest Service, Bugwood.org 768x512 / 1536x1024
Figure 1. Adults of the carpenterworm, Prionoxystus robiniae; female (left) and male (right)
Female carpenterworm, center, in natural position Gerald J. Lenhard, Louiana State Univ, Bugwood.org 768x512 / 1536x1024
Figure 2. Female carpenterworm, center, in natural position Figure 3. Larvae of carpenterworm Figure 4. Larval gallery of carpenterworm (top) and surface injury from lateral gallery in trunk (bottom)
Staining and oozing are signs making the point of entrance for carpenterworms Larry R. Barber, USDA Forest Service, Bugwood.org 768x512 / 1536x1024
Tunnels of carpenterworms in elm USDA Forest Service - Ogden Archive, USDA Forest Service, Bugwood.org 768x512 / 1536x1024
Ash logs at harvest Theodor D. Leininger, USDA Forest Service, Bugwood.org 768x512 / 1536x1024
Defects in milled wood from carpenterworm tunnels and staining James Solomon, USDA Forest Service, Bugwood.org 768x512 / 1536x1024
Figure 5. Staining and oozing are signs making the point of entrance for carpenterworms Figure 6. Tunnels of carpenterworms in elm (left) and ash (right) logs at harvest Figure 7. Defects in milled wood from carpenterworm tunnels and staining

Important biological control agents related to this pest species

Little is know about the natural control of carpenterworms. Woodpeckers prey on larvae. Parasitism appears to be minimal.

Web links for information on carpenterworm

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