Distribution of Arsenic in MSMA-Treated Lodgepole Pines Infested by the Mountain Pine Beetle, Dendroctonus ponderosae (Coleoptera: Scolytidae), and Its Relationship to Beetle Mortality

Abstract

The LC50 of MSMA (monosodium methanearsonate) for first- and second-instar mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins, mining for 4 d in ground phloem tissue impregnated with methane arsonic acid (CH3AsO3H2), the pure form of arsenic in MSMA, was 102 ppm. Application of MSMA 3 wk after attack to axe-frills (cuts) near the root collar of five lodgepole pines, Pinus contorta var. latifolia Engelmann, resulted in high accumulations of arsenic in phloem and sapwood near the point of application and in foliage 11 wk later. MPB taken from bolts cut from MSMA-treated trees 1 m above the axe-frill were all dead. There was a strong relationship between amounts of arsenic in MPB and those in phloem tissue up to 2 m. At sampling points above 2 m on treated trees, arsenic residues in phloem and sapwood were, on average, not significantly different from those occurring naturally in tissues of lodgepole pine. Enough arsenic could have passed through the tissues to kill or inhibit the brood MPB within the trees, but MPB mortality was probably due to an interaction of many factors including moisture deficit and fungal invasion of the host tree.