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Rapid Pest Risk Analysis for Lambdina fiscellaria


Executive Summary
The hemlock looper, Lambdina fiscellaria, is a North American forest pest of coniferous and broadleaved trees. The pest has a complicated taxonomy. It is widely reported as having three subspecies on the basis of differences in feeding preferences of the larval stages, but there are no morphological differences and some authors argue the pest should be treated as a single species. All three subspecies are considered in this PRA, which examines the risk of this pest to the island of Ireland (the PRA area), consisting of Ireland and Northern Ireland.

Lambdina fiscellaria fiscellaria, also known as the eastern hemlock looper, is distributed in eastern North America and larvae show a preference for Abies balsamea (balsam fir) but will also feed on Picea glauca (white spruce), Tsuga canadensis (eastern hemlock) and a number of broadleaved trees. Lambdina fiscellaria lugubrosa, also known as the western hemlock looper, is distributed in the Pacific Northwest, with a larval feeding preference of Tsuga heterophylla (western hemlock), though the pest has also been recorded infesting stands of Picea sitchensis (Sitka spruce). Lambdina fiscellaria somniaria, also known as the Garry oak looper or western oak looper, is found in Oregon, Washington and south coastal British Columbia and shows a strong preference for Quercus garryana (Garry oak) as larvae, sometimes spreading into Pseudotsuga menziesii plantations.

All three subspecies cause periodic mass outbreaks in forest stands in North America which have very large economic impacts. The fist instars (very young caterpillars) of L. fiscellaria require freshly flushed foliage in order to survive, but as larvae mature they can feed on older foliage. During outbreak years, larvae can be found feeding on a significant number of tree species as well as understory plants. Recorded outbreaks have led to high mortality of trees and losses in timber. For example between 1910 and 1975, Natural Resources Canada estimate outbreaks of L. f. fiscellaria have caused losses of 36 million cubic metres of timber in the provinces of Newfoundland and Quebec. Economic impacts of the pest in its current distribution are very large, with low uncertainty.

Lambdina fiscellaria is considered unlikely to enter the PRA area. The pest is largely restricted to forested areas, and reports of infestations in nurseries are rare. Damage to trees is normally severe enough that plants would be unmarketable, making entry in association with plants for planting very unlikely. Lambdina fiscellaria lays its eggs, and pupates within, the mosses and lichens found on the trunks and branches of trees as well as fallen logs, stumps and the forest floor. In North America, these mosses and lichens are sometimes harvested and exported, fresh, including to the UK which includes Northern Ireland, within the PRA area. First instar larvae of L. fiscellaria do have some natural dispersal capacity, as eggs are often not laid directly on suitable host trees, and so there is a risk of larvae hatching from eggs inadvertently imported along this pathway and transferring to a suitable host, depending on the final use of the mosses and lichens. Overall likelihood of entry on this pathway was rated as unlikely, with high uncertainty, as more information is required on the final use of imported fresh mosses and lichens from the USA. Wood that has not been subject to any treatments (e.g. debarking, heat treatment) is also considered to pose a risk of introducing the pest, as egg masses and pupae may be associated with this commodity. Woods of the preferred hosts of L. fiscellaria are subject to phytosanitary measures that should eliminate the risk of the pest being associated with the commodity, but during outbreak year’s pupation and egg laying may occur on a very diverse range of timber species. Overall risk of entry on this pathway is unlikely, with high uncertainty.

The different subspecies of L. fiscellaria were judged to have different risks of establishing in the PRA area. All three subspecies are present in regions with similar climates to the PRA area, though L. f. fiscellaria is generally present in regions which have colder winters. It is uncertain if L. fiscellaria could adapt to feed on species within the PRA area as its primary host, especially L. f. somniaria which shows a very strong preference for Quercus garryana, a species not found in the PRA area. Likelihood of establishment of L. f. somniaria is moderately likely with high uncertainty, as it is unknown if larvae could adapt to feed on European species of oak. Likelihood of establishment of L. f. fiscellaria was rated as likely, with high uncertainty – this is because of the potential for the milder winters of the PRA area to cause earlier egg hatch of this subspecies. There may potentially be asynchrony between egg hatch and bud burst of suitable hosts, meaning larvae would starve. It is also uncertain if this subspecies could adapt to using P. sitchensis or other hosts grown in the PRA area as a primary host. Likelihood of establishment of L. f. lugubrosa is very likely with medium uncertainty; this species is present in regions with a very similar climate to the PRA area and feeds on hosts that are widespread on the island of Ireland including P. sitchensis.

Potential impacts in the PRA area are subject to high uncertainty. This is due to several reasons, one of the main reasons is it is uncertain what hosts in the PRA area will prove to be suitable for L. fiscellaria. It is also uncertain if conditions in the PRA area are suitable for the build up of outbreak populations. Most outbreaks in North America initiate in mature or over-mature coniferous stands (>100 years old), and the majority of coniferous stands in the PRA are < 50 years old. The pest also has a low capacity for natural spread. Lambdina fiscellaria are slugglish fliers, especially females that are heavily burdened by eggs and cannot fly long distances. This means that should the pest be introduced, industry would be able to adapt by developing monitoring and control techniques well ahead of the pest reaching its maximum distribution within the PRA area. Containment of outbreaks is also feasible due to the pest’s limited dispersal capacity, but outbreaks could still occur on a local scale and cause defoliation and death of trees. Potential economic impacts in the PRA area were rated as moderate, with high uncertainty.

Potential environmental impacts are also highly uncertain, as this will depend on where outbreaks occur and again, what species L. fiscellaria may be able to feed on in the PRA area. Environmental impacts may also be incurred if control measures such as felling or aerially spraying of control products is necessary, and potential environmental impacts were rated as moderate with high uncertainty.

Lambdina fiscellaria may cause social impacts by causing outbreaks in forested areas used for recreation, defoliating trees and killing them, reducing their aesthetic value. Killed trees may also pose a safety hazard, meaning public access has to be limited to some sites. Visitor numbers may be reduced as infested sites, leading to knock on impacts for the local economy. Potential social impacts in the PRA area are rated as moderate, with high uncertainty.

Exclusion is the best risk management option for the pest. Lambdina fiscellaria is a potential pest not only for the island of Ireland but for a number of EU Member States. Since it is absent from the EU, it could be regulated as a quarantine pest in the plant health legislation (Plant Health Directive 2000/29/EC). It is recommended that this pest is subject to a PRA at EU or EPPO level to further analyse if regulation of the pest is technically justified.

More research is needed to ascertain what the potential host range of L. fiscellaria in the PRA area could be. In addition, there needs to be further analysis to ascertain if egg hatch of L. fiscellaria in the PRA area would occur in relative synchrony with bud burst, which is necessary for high survival of the first instar larvae.


  • Lambdina fiscellaria
  • Lambdina fiscellaria lugubrosa
  • Lambdina fiscellaria somniaria


  • Abies balsamea
  • Picea glauca
  • Picea sitchensis
  • Pseudotsuga menziesii
  • Quercus garryana
  • Tsuga canadensis
  • Tsuga heterophylla


Type File Size
Pest Risk Analysis Download 1,13MB

PRA Area

  • Ireland