Pesticide Treatments Affect Mountain Pine Beetle Abundance and Woodpecker Foraging Behavior

Abstract

In British Columbia, Canada, management efforts used to control mountain pine beetle (Dendroctonus ponderosae Hopkins) outbreaks have included treatment of infested trees with an organic arsenic pesticide, monosodium methanearsonate (MSMA). Cumulative pesticide applications over a large geographic area have generated concerns about arsenic loading in the environment and potential toxicity to nontarget wildlife. We investigated woodpecker foraging patterns in infested stands with and without MSMA treatment using a combination of tree debarking indices, point count surveys, and radiotelemetry methods in addition to insect flight traps to measure mountain pine beetle emergence. Debarking indices indicated woodpecker foraging of MSMA-treated trees was significantly lower than nontreated trees in all sampling years. However, approximately 40% of MSMA trees had some evidence of foraging. Focal observations of foraging woodpeckers and point count surveys in MSMA treatment areas further confirmed that several species of woodpeckers regularly used MSMA stands during the breeding season. Radio-tagged Hairy (Picoides villosus) and Three-toed (Picoides dorsalis) Woodpeckers spent on average 13% and 23% (range 0-66%) of their time, respectively, in treated stands, despite the fact that these areas only comprised on average 1-2% of their core home range (1 km2). MSMA strongly reduced the emergence of several bark beetle (Coleoptera, Scolytidae) species including the mountain pine beetle, and there was a highly significant positive relationship between Dendroctonus beetle abundance and Three-toed Woodpecker abundance. This study identifies the potential negative impact that forest management practices using pesticides can have on woodpecker populations that depend on bark beetles and their host trees.

Foraging Behaviour in Magellanic Woodpeckers Is Consistent with a Multi-Scale Assessment of Tree Quality

“…Previous studies suggest that Magellanic woodpeckers feed preferentially on standing trees that exhibit an advanced decay stage [ 32 , 34 , 38 , 39 ]. These preferences are consistent with natural and experimental studies that demonstrate the ability of woodpeckers to recognize the type and amount of food (e.g., larvae) present in trees (e.g., [ 40 – 42 ]). Although theoretical studies suggest that foraging woodpeckers respond perceptually and cognitively to habitat heterogeneity over different spatial scales [ 43 ], the spatio-temporal scales at which woodpeckers assess the tree quality in the wild remains to be determined.…”

Trophic Transfer of Arsenic from an Aquatic Insect to Terrestrial Insect Predators

“…Arsenic accumulation was similarly negligible in mice living in a contaminated seasonal wetland, whose diet consisted of seeds, plants, and arthropods that accumulated significant concentrations of arsenic (up to 0.419 mg kg −1 in arthropod prey) [23]. In contrast, studies addressing the affects of organoarsenical pesticides on woodpeckers and their prey, the mountain pine beetle, found that the birds accumulated potentially toxic levels of arsenic from the beetles [24], and that these levels caused both lethal [25] and sublethal [26] effects. The much more toxic effects of arsenic moving up the food chain in these studies may be the result of the organic form of arsenic in which beetles and birds were exposed versus inorganic forms in the Hopkins et al [22] and Torres and Johnson [23] studies, as well as the concentrations accumulated in the mountain pine beetles.…”

“…The trophic transfer of arsenic between an invertebrate prey and insect [16]–[19] or vertebrate [20], [21] predators has been documented for aquatic systems. However, in terrestrial systems, trophic transfer of arsenic has only been evaluated for movement to vertebrate predators [22]–[26].…”

Chemical control in forest pest management

“…As the beetles are dead, the trap tree does not have to be burned on site or removed, but simply allowed to decompose. MSMA treatment was favoured in British Columbia, because it was effective, relatively inexpensive and easy to apply in remote areas (British Columbia Ministry of Forests 1995;Morrissey et al 2008). From 1995 to 2004, 5080 kg of MSMA was applied to almost 500 000 trees in British Columbia for mountain pine beetle control (Morrissey et al 2007).…”