The non-target effects of anazadirachtin-based systemic insecticide used for control of wood-boring insect pests in trees were assessed on litter-dwelling earthworms, leaf-shredding aquatic insects, and microbial communities in terrestrial and aquatic microcosms. The insecticide was injected in to the trunks of ash trees at a rate of 0.2g azadirachtin / cm tree diameter in early summer. At the time of senescence, foliar concentrations in most (65%) leaves where at or below detection (0.01 mg/kg total azadirachtin) and the average concentration among leaves over all at senescence was 0.19 mg/kg. Leaves from the azadirachtin-treated trees at senescence were added to microcosms and responses by test organisms were compared to those in microcosms containing leaves from non-treated ash trees (controls). No significant reductions were detected among earthworm survival, leaf consumption rates, growth rates, or cocoon production, aquatic insect survival and leaf consumption rates, and among terrestrial and aquatic microbial decomposition of leaf material in comparison to controls. In a further set of microcosm tests containing leaves from intentional high-dose trees, the only significant, adverse effect detected was a reduction in microbial decomposition of leaf material, and only at the highest test concentration (aprox. 6 mg/kg). Results indicated no significant adverse effects on litter-dwelling earthworms or leaf-shredding aquatic insects at concentrations up to at least 30X the expected field concentrations at operational rates, and at 6X expected field concentrations for adverse effects on microbial decomposition. We conclude that when azadirachtin is used as a systemic insecticide in trees for control of insect pests such as the invasive wood-boring beetle, emerald ash borer, resultant foliar concentrations in senescent leaf material are likely to pose little risk of harm to decomposer invertebrates.
Ecotoxicology and Environmental Safety (2011 in press)
David Kreutzweiser, Dean Thompson, Susana Grimalt, Derek Chartrand, Kevin Good, and Taylor Scarr