Although important for forest regeneration, the Mountain Pine Beetle outbreak has become the largest insect epidemic ever recorded in North America. Warm winters and dry summers during the mid-1990s, combined with fire suppression and an increase in monoculture plantations, have caused a population explosion that has destroyed half of the commercial pine in British Columbia. It is projected that by 2015 almost 70% of harvestable pine in the interior of the province will be affected.

From 1995 to 2004, in an attempt to control the outbreak, forest workers applied 5000 kg of monosodium methanearsonate (MSMA)--a toxic pesticide containing arsenic--to half a million trees across 14% of British Columbia.

As the only pesticide registered for Mountain Pine Beetle control in the province at the time, MSMA presented an easy and affordable option for industry response. Relatively small amounts of the chemical were injected directly into trees, quickly killing both the beetle and the tree. The direct application was thought to reduce the risk of widespread contamination posed by traditional aerial spraying. However, concerns soon arose that treating large swaths of forests with arsenic-based pesticides could impair ecosystem functioning and reduce the biodiversity and productivity of the region.

It was unclear, and in some cases unknown, how MSMA would affect wildlife. Without concrete scientific data, it was difficult for resource managers to determine the best course of action.

Seeking Solutions through S&T

In 2002, wildlife toxicologists at Environment Canada began a series of studies, in partnership with researchers at Simon Fraser University (SFU) and the University of British Columbia (UBC), to understand how MSMA might affect the beetle’s natural predators, namely woodpeckers and other forest birds.

Scientists collected beetles and conducted arsenic analysis. Beetles were found to survive high concentrations of MSMA and, when ingested, were extremely toxic to woodpeckers. Studies indicated that the pesticide was actually 30% less effective at killing the insect than previously thought.

The MSMA method also involved pre-baiting, using Mountain Pine Beetle pheromone packs, which concentrated beetles in the treatment zones. Using radio transmitters, researchers found that woodpeckers, as insectivores, were attracted to areas of beetle outbreaks and spent a disproportionate amount of time in MSMA-treated stands, consuming many thousands of beetles a day and increasing their exposure to the chemical.

MSMA was less acutely toxic than some other forms of arsenic, but laboratory analysis showed that it became much more potent as it was metabolized. Ingestion exposed the birds to a highly toxic intermediate during metabolic conversion. This may have been the toxic mechanism causing the observed effect of substantial weight loss in woodpeckers.

Researchers also analyzed arsenic residue in woodpecker blood and feathers. They found that high concentrations and long-term exposures made the birds susceptible to reproductive dysfunction, behavioural abnormalities, growth reductions and even death.

Impact On Decision Making

As early as 2003, Environment Canada scientists presented preliminary findings to scientific audiences at the United States / Mexico Pesticide Information Exchange Program and the Society for Environmental Toxicology and Chemistry. Encouraged by interest and additional funding, the research team conducted further studies until, in 2005, they had sufficient information to show that MSMA posed a significant risk to forest birds. They decided to convene a workshop where stakeholders could exchange information on MSMA.

Twenty-eight participants--representing federal and provincial governments, the Workers’ Compensation Board, UBC, SFU, industry consultants and concerned citizens--discussed MSMA, its use and effects. The science presented helped convince British Columbia’s Ministry of Environment to use the new Integrated Pest Management Act to revoke the province’s permit to use MSMA.

The high-profile action increased awareness of organic arsenicals in the United States, where MSMA is still used. In 2006, the United States Environmental Protection Agency (US EPA) decided to regulate arsenic-based pesticides, including MSMA, due to concerns over human and environmental health. As of 2011, it is used only on cotton crops, with restrictions in place to protect drinking water. The US EPA is currently phasing out the use of organic arsenicals in favour of lower-risk chemicals.

In the face of scientific evidence, the US EPA decision, public pressure and mounting evidence that existing management activities were not containing the beetle problem, British Columbia’s Ministry of Forests, Lands and Natural Resources Operations and its Range Program destroyed remaining stocks and did not pursue further use of MSMA.

One problem remained: what to do with the half a million “legacy trees” treated with MSMA. Did they still pose risks? In 2004, an audit by the Forest Practices Board recommended that a policy be developed to guide the management of legacy trees.

To develop this policy framework, British Columbia’s Ministry of Forests, Lands and Natural Resources Operations and its Range Program hosted a public forum at which Environment Canada and other government institutions, non-governmental organizations, academia, industry and other stakeholders met to develop a policy framework and make recommendations to the provincial Chief Forester on how to incorporate and manage legacy trees. In 2007, a final policy was released that guides action for legacy trees and provides clear procedures on how pesticides for Mountain Pine Beetle control are to be introduced.

The Ministry developed an MSMA website featuring information, databases and maps of legacy trees and the health and environmental risks associated with the chemical.

Benefits to Canadians

British Columbia represents 16% of Canada’s forested area but accounts for over half of Canada’s forestry production, valued at $10 billion in 2008, or almost 1% of the nation’s gross domestic product. Although the Mountain Pine Beetle outbreak has slowed in recent years, impacts on the forestry industry are still being felt.

Organic arsenicals, including MSMA, have been banned in Canada. Environment Canada’s collaborative research contributed to a greater understanding of the efficacy and effects of MSMA, and showed that assumptions about the efficacy and safety of the product were incorrect.

Scientists were concerned that effects of MSMA, in combination with altered availability of food and reduced habitat--due to beetle damage and increased logging--might make woodpeckers susceptible to other stressors and population decline. Loss of the beetle’s natural predators from the ecosystem could allow further expansion of the beetle population and the resulting damage could intensify.

With the MSMA threat to woodpeckers eliminated, their role as a beetle predator can function more naturally in the forest ecosystem. This research has contributed to a more environmentally responsible approach to integrated pesticide management within forest ecosystems, bringing economic and environmental benefits to all Canadians.

For more information:

Albert, C.A., T.D. Williams, C.A. Morrissey, V.W.M. Lai, W.R. Cullen, and J.E. Elliott. 2008. Dose-dependent uptake, elimination and toxicity of monosodium methanearsonate in adult zebra finches (Taeniopygia Guttata). Environmental Toxicology and Chemistry 27(3): 605-611.

Morrissey, C.A., C. A. Albert, P.L. Dods, W.R. Cullen, V.W.M. Lai, and J.E. Elliott. 2007. Arsenic Accumulation in Bark Beetles and Forest Birds Occupying Mountain Pine Beetle Infested Stands Treated with Monosodium Methanearsonate. Environmental Science and Technology 41(4): 1494-1500.

Morrissey, C.A., P.L. Dods, and J.E. Elliott. 2008. Pesticide treatments affect mountain pine beetle abundance and woodpecker foraging behavior. Ecological Application 18(1): 172-184.

Morrissey, C. and J.E. Elliott.  2011. “Toxic trees: arsenic pesticides, woodpeckers and the mountain pine beetle,” In J.E. Elliott, C.A. Bishop, and C.A. Morrissey (eds.), Wildlife Ecotoxicology: Forensic Approaches, Springer, New York, pp 239-266.

Reimer, K.J., and W.R. Cullen. 2009. Arsenic concentrations in wood, soil and plant tissue collected around trees treated with monosodium methanearsonate (MSMA) for bark beetle control. Report prepared for the British Columbia Ministry of Forests and Range.