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1 March 2009 Impacts of Ultra-Low Volume Resmethrin Applications on Non-Target Insects
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Abstract

We studied the impacts of exposure to ultra-low volume (ULV) applications of resmethrin (Scourge®) on monarch butterfly (Danaus plexippus) larvae and adults. In a series of 3 experiments, we measured short- and long-term survival of monarch larvae and adults, and the impacts of consuming previously exposed host plants on monarch larvae. We measured efficacy during all experiments with caged sentinel mosquitoes, and during Experiments 1 and 2 with pretreatment, treatment, and posttreatment measurements of mosquito abundance in CO2 traps. Downwind monarch larval and adult mortality were higher than upwind or control mortality up to 120 m, but not 170 m, from the spray path. In 1 experiment, monarchs exposed to spray as larvae developed into smaller adults, suggesting sublethal impacts. Milkweed host plants sprayed 1, but not 2 or 4 days previously, resulted in increased monarch larval mortality. Sentinel mosquito mortality was generally high, and CO2 traps revealed substantially lower mosquito abundance immediately after the treatment (>90% reduction) but <20% reduction 24 h after treatment. Our results suggest that ULV resmethrin applications will impact lepidopteran larvae and adults that are directly exposed to the spray but that generalizations about other nontarget taxa will require additional research. The magnitude of population-level impacts on monarchs will depend on the proportion of the population that is exposed.

Karen S. Oberhauser, Stephen A. Manweiler, Rosemary Lelich, Meredith Blank, Rebecca V. Batalden, and Alma de Anda "Impacts of Ultra-Low Volume Resmethrin Applications on Non-Target Insects," Journal of the American Mosquito Control Association 25(1), 83-93, (1 March 2009). https://doi.org/10.2987/08-5788.1
Published: 1 March 2009
JOURNAL ARTICLE
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