Forest Pest Insects in North America: a Photographic Guide

Pine false webworm

Acantholyda erythrocephala (L.) (Hymenoptera: Pamphiliidae)

Orientation to pest

Pine false webworm, Acantholyda erythrocephala (L.), is an introduced pamphiliid sawfly of European origin that is now present in several parts of eastern North America and Canada. It feeds on several pines. Winter is passed as prepupae, which pupate in the spring. Adults emerge soon after and lay eggs in short rows of 3 to 10 in small slits cut into last year' needles. Young larvae spin loose webs in which they feed gregariously on old needles, which they cut off and then pull into the web to eat. Older larvae are solitary and feed from silken tubes bound to twigs. Frass and bits of needles stick to these silk tubes. When mature, larvae drop to the ground and build the earthen cells and overwinter as prepupae. Heavy infestations can defoliate hosts and cause tree mortality.

Hosts commonly attacked

This sawfly feeds especially on eastern white (Pinus strobus L.) and red (Pinus resinosa Sol. ex Aiton), but also Scotch (Pinus sylvestris L.), Austrian (Pinus nigra J.F. Arnold), and Japanese red (Pinus densiflora Siebold & Zucc.) pines.

Distribution

This sawfly is found in New England, New York, New Jersey, Pennsylvania, Wisconsin, Minnesota, Newfoundland, Alberta, Quebec, and Ontario.

Images of pine false webworm

Adult (male on right and female on left) of pine false webwormin copula Barry Lyons, Canadian Forest Service, Bugwood.org 768x512 / 1536x1024
Adult female ovipositing on red pine foliage Barry Lyons, Canadian Forest Service, Bugwood.org 768x512 / 1536x1024
Eggs of pine false webworm on red pine foliage Barry Lyons, Canadian Forest Service, Bugwood.org 768x512 / 1536x1024
Figure 1. (Left) Adult (male: right; female: left) of pine false webworm, Acantholyda erythrocephala, in copula, and (right) adult female ovipositing on red pine foliage Figure 2. Eggs of pine false webworm on red pine foliage
Neonate larva of pine false webworm emerging from the egg Barry Lyons, Canadian Forest Service, Bugwood.org 768x512 / 1536x1024
Ultimate instar larva climbing on silk strands outside the web Barry Lyons, Canadian Forest Service, Bugwood.org 768x512 / 1536x1024
Damage (shoots with clipped off needles) by pine false webworm on young plantation-grown red pine Barry Lyons, Canadian Forest Service, Bugwood.org 768x512 / 1536x1024
Defoliation in pine plantations in Simcoe Co., Ontario, due to pine false webworm Barry Lyons, Canadian Forest Service, Bugwood.org 768x512 / 1536x1024
Figure 3. (Left) Neonate larva of pine false webworm emerging from the egg, and (right) ultimate instar larva climbing on silk strands outside the web Figure 4. Damage (shoots with clipped off needles) by pine false webworm on young plantation-grown red pine Figure 5. Defoliation in pine plantations in Simcoe Co., Ontario, due to pine false webworm

Important biological control agents related to this pest species

Since this is an invasive species in North America, the parasitoids from its native range in Europe have been investigated for introduction. The most important such species is the tachinid Myxexoristops hertingi Mesnil, which has been released in Ontario, Canada.

Web links for information on pine false webworm

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