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.
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1 March 2009
Impacts of Ultra-Low Volume Resmethrin Applications on Non-Target Insects
Karen S. Oberhauser,
Stephen A. Manweiler,
Rosemary Lelich,
Meredith Blank,
Rebecca V. Batalden,
Alma de Anda
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Journal of the American Mosquito Control Association
Vol. 25 • No. 1
March 2009
Vol. 25 • No. 1
March 2009
Adult mosquito control
monarch butterflies
nontarget impacts
resmethrin
ultra-low volume ground applications