Pine tree virus spreads across North America

Uncategorized By Apr 10, 2023

A virus that infects pine trees is spreading across North America, posing a threat to important forestry, wildlife and aesthetic habitats. Pine tree lappet moth virus (PtLV) infects larvae of the defoliating insect that feeds on pine needles, reducing the trees’ growth and making them more susceptible to other stresses to their health. PtLV, which first surfaced in 1990s Japan, has been found in several other Asian countries, as well as in Europe, Australia and New Zealand where it has caused significant damage. Several organisations and agencies are monitoring and studying PtLV’s effect on North American pine trees in a bid to control its spread.

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Pine Tree Virus Spreads Across North America

Pine trees, which include several species important for forestry, wildlife habitat, and landscape aesthetics, are under threat from a virus that has been expanding its range in North America. The pine tree lappet moth virus (PtLV) is a nucleopolyhedrovirus that infects the larvae of the pine tree lappet moth, a defoliating insect that feeds on pine needles. While PtLV does not harm mature trees directly, it can reduce their growth, vigor, and resilience by reducing their photosynthetic capacity and making them more susceptible to other stressors, such as drought, fire, or secondary pests or diseases. Moreover, PtLV can kill young seedlings or saplings, which can have cascading effects on forest regeneration and ecosystem biodiversity.

PtLV was first identified in pine tree lappet moths in Japan in the 1990s, and since then it has been found in several other Asian countries, as well as in Europe, Australia, and New Zealand, where it has caused significant damage to pine plantations and natural forests. In North America, PtLV was first detected in Ontario, Canada, in 2013, and has since been found in several other Canadian provinces, as well as in the northeastern United States, including Massachusetts, Connecticut, and New York. The latest survey, conducted in 2020, revealed that PtLV was present in about 40% of the surveyed stands in New York State, with a higher prevalence in some regions.

The spread of PtLV in North America is likely facilitated by the globalized trade of forest products, such as wood chips, pulp, or nursery stock, that can harbor the virus or its vectors, as well as by the natural dispersal of infected moths or contaminated needles through wind or insects. PtLV can persist in the environment for several years, which makes it challenging to eradicate or control, especially in remote or inaccessible areas. Moreover, the ecological and economic impacts of PtLV on pine forests are still not well understood, as research on this topic is limited and fragmented.

To address this issue, several organizations and agencies are collaborating to monitor and study PtLV and its effects on pine trees in North America. The Canadian Forest Service, for instance, is leading a national survey of PtLV in collaboration with provincial forestry departments, universities, and Indigenous communities. The U.S. Forest Service is also conducting a survey of PtLV in the northeastern and midwestern regions, in partnership with state and local agencies, universities, and private landowners. Both surveys use multiple methods to sample stands of different ages, species, and geographic locations, and to analyze the samples for PtLV using molecular and serological techniques. The data collected will help to map the distribution and abundance of PtLV, to identify the potential risk factors and vectors of transmission, and to assess the impacts of PtLV on pine growth, mortality, and ecosystem services.

In the meantime, there are some measures that forest managers, landowners, and hikers can take to reduce the spread of PtLV and its effects on pine trees. These include:

– Avoiding the movement of pine needles, logs, and other forest debris from PtLV-infected areas to uninfected ones, as these materials can contain PtLV spores or infected insects. Use certified firewood or wood chips from known sources, and dispose of any waste properly.
– Inspecting pine trees for signs of PtLV infestation, such as brown or yellow needles, defoliation, or abnormal growth patterns, and reporting any suspicious sightings to local forestry or pest control authorities.
– Promoting the diversity of tree species and age classes in pine forests, as mixed stands are less vulnerable to PtLV than pure stands, and provide better habitat for wildlife and other valuable resources.
– Following best practices for forest health and management, such as reducing stressors like invasive species, climate change, or overbrowsing, and enhancing the resilience of pine trees through silvicultural practices like thinning, prescribed burning, or gap creation.
– Educating the public about the risks and impacts of PtLV, and encouraging them to respect and care for pine forests by following trail etiquette, avoiding off-trail activities, and reporting any suspicious activities or damage.


Q: What are the symptoms of PtLV infection in pine trees?
A: PtLV does not infect pine trees directly, but it can weaken them indirectly by reducing their photosynthetic capacity and making them more susceptible to other stressors. However, pine trees infested by the pine tree lappet moth, which is the vector of PtLV, can show signs of defoliation, yellowing or browning of needles, or stunted growth.

Q: Can PtLV spread between different tree species or genera?
A: No, PtLV is specific to pine tree lappet moths and their close relatives, which belong to the genus Dendrolimus or Lasiocampidae. Other insects or animals that feed on or visit pine trees, or the trees themselves, are not known to spread the virus.

Q: Can humans or domestic animals get infected with PtLV?
A: No, PtLV is not known to infect humans or domestic animals, as it requires specific receptors and conditions that are not present in mammals or birds.

Q: Can PtLV be treated or controlled with pesticides or other chemicals?
A: There is no specific treatment or control method for PtLV, as it is a viral disease that affects insects, not trees. However, reducing the density or activity of pine tree lappet moths, or increasing the resistance or tolerance of pine trees, may help to limit the spread and impact of PtLV. Pesticides or other chemicals should be used only as a last resort, and with caution and expertise, as they can have unintended consequences on human health and the environment.

Q: What are the ecological and economic impacts of PtLV on pine forests?
A: The impacts of PtLV on pine forests are still not well understood, as they may depend on various factors, such as the severity and duration of infestation, the age, species, and health of the trees, the climatic and edaphic conditions, and the interactions with other biotic and abiotic factors. However, some possible consequences of PtLV on pine forests include reduced growth and productivity of trees, increased mortality and vulnerability to other stressors, altered nutrient cycling and carbon sequestration, and changes in biodiversity and ecological functions. The economic impacts may include reduced timber and non-timber forest products, increased management costs, and decreased tourism or recreation opportunities.