Toxic Trees: Arsenic Pesticides, Woodpeckers, and the Mountain Pine Beetle

Abstract

During the mid-1990s, an unprecedented outbreak of the Mountain Pine Beetle (Dendroctonus ponderosae) in the economically valuable pine forests of British Columbia triggered a major campaign by forest managers to try and control the beetle damage. The result was a major change in the landscape from harvesting and prescribed burns in addition to the wide scale application of a systemic insecticide known as monosodium methanearsonate (MSMA). Since MSMA contains arsenic, is highly stable, and was being applied in increasingly large quantities, our study evaluated the potential impacts to forest birds, particularly woodpeckers. From 2002 to 2006, we investigated the exposure of breeding woodpeckers to MSMA ingested via contaminated bark beetles. We measured high levels of arsenic in beetles from treated trees, and found that significant amounts of debarking on many MSMA-treated trees indicating woodpeckers were feeding on them. Radio-telemetry confirmed that woodpeckers breeding near MSMA treatments regularly used those stands. Blood samples of woodpeckers and other forest birds revealed elevated arsenic concentrations. Through a concurrent laboratory dosing study of Zebra finches (Taeniopygia guttata), we estimated that woodpeckers were receiving enough MSMA through ingestion of contaminated beetles to cause poorer growth and mortality of young birds and mass loss in adults. We concluded that the combination of extensive harvesting in the region in combination with the large numbers of treated MSMA trees was potentially detrimental to forest bird populations. By the end of our study, MSMA approval for use in Canada was revoked and the Ministry of Forests did not pursue re-registration of MSMA. We clearly demonstrated that large-scale MSMA use had the potential to cause serious harm to forest birds, while appearing to have limited efficacy in beetle control. This was a landmark study in the field of wildlife ecotoxicology – a first to evaluate the exposure and effects of a toxic chemical to woodpeckers in forest ecosystems.