Impacts of Ultra-Low Volume Resmethrin Applications on Non-Target Insects

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.

Monarchs in decline: a collateral landscape‐level effect of modern agriculture

“…() offered insights into the survival of immature monarchs from egg to fifth instar. Causes of immature monarch mortality include abiotic factors such as temperature (Zalucki, ; York & Oberhauser, ; Nail et al ., ) and insecticides (Oberhauser et al ., , ), as well as biotic factors including resource quality and availability (Malcolm, ; Malcolm & Zalucki, ; Zalucki & Lammers, ), disease (Altizer & Oberhauser, ), and natural enemies (Calvert, ; Oberhauser et al ., ; Stenoien et al ., ; McCoshum et al ., ). Mean summer survival of monarchs from egg to adulthood was estimated to be 5.8% in the North Central United States.…”

Aerial Ultra-Low-Volume Application of Naled: Impact on Nontarget Imperiled Butterfly Larvae (Cyclargus thomasi bethunebakeri) and Efficacy Against Adult Mosquitoes (Aedes taeniorhynchus)

“…As the small droplets do not settle quickly, they are capable of drifting extended distances with deposition occurring both within and beyond the target area. Oberhauser et al (2006Oberhauser et al ( , 2009) assessed the impact of permethrin residues and ULV applications of resmethrin (Scourge) on monarch butterßy larvae and adults. Their results indicated that both life stages suffer mortality if directly exposed to residues on host plants or by direct downwind applications, but the extent of impact on the larger monarch butterßy population depends on the proportion of the host plants or individual organisms exposed.…”

An Evaluation of Studies on the Potential Threats Contributing to the Decline of Eastern Migratory North American Monarch Butterflies (Danaus plexippus)

“…Studies also confirmed that range overlap with Bt-exposed fields Pleasants et al, 2001) could contribute to lower reproductive output (Stenoien et al, 2015), though larval mortality is not always associated with proximity to Bt-exposed fields (Zangerl et al, 2001). Similarly, insecticide use showed effects on individual survival (pyrethroids, Oberhauser et al, 2006Oberhauser et al, , 2009clothianidin, Pecenka andLundgren, 2015, λ-cyhalothrin, Stanley-Horn et al, 2001) and herbicide application (i.e., glyphosate) is known to influence population size (Thogmartin et al, 2017b). However, the strength of the effects varied depending on the agrochemical (i.e., significant effects not shown for dicamba and 2,4-dichlorophenoxyacetic acid use, Thogmartin et al, 2017b), geographic location (Thogmartin et al, 2017b), and life stage (Pan et al, 2017).…”