In January 2024 adult monarch butterflies (Danaus plexippus (Linnaeus, 1758)) were found dead near their overwintering site in Pacific Grove, Monterey County, California, USA. Ten of the deceased monarchs (six females and four males) were collected from three sites by staff at the Pacific Grove Museum of Natural History and sent to the U.S. Geological Survey Organic Chemistry Research Laboratory for analysis. Each individual adult monarch was analyzed following methods in Black et al., 2023 and Gross et al., 2024a and 2024b for 181 pesticides and pesticide transformation products; 15 pesticides were detected and included 8 insecticides/insecticide transformation products, 2 fungicides, and 4 herbicides/herbicide transformation products. Concentrations of individual pesticides ranged from 1.0 to 2,645 nanograms per gram (ng/g) dry weight. Concentrations were highest for three pyrethroid insecticides; bifenthrin ranged from 18.8 to 855.3 ng/g, cypermethrin 6.7 to 2,645.1 ng/g and permethrin from not detected (less than 1.0 ng/g) to 1,349.3 ng/g, all other pesticides detected were less than 25 ng/g.

Wild bee and butterfly samples were collected from the margins of agricultural fields located on five Conservation Areas in Missouri. In 2016 and 2017, samples were collected and composited by genera for a total of 90 samples. Samples were extracted via pressurized liquid extraction and solid phase extraction cleanup. Samples were analyzed for 168 pesticides and degradates using both gas and liquid chromatography-tandem mass spectrometry. Overall, 16 pesticides were detected. Pesticides detected in greater than 2% of the composite samples included: metolachlor (24%), tebuconazole (22%), atrazine (18%), imidacloprid desnitro (13%), bifenthrin (9%), flumetralin (9%), p,p’-DDD (6%), tebupirimfos (4%), fludioxonil (4%), flutriafol (3%), cyproconazole (2%), and oxadiazon (2%). Concentrations for individual pesticides ranged from 2 to 174 ng/g. Results indicate that wild pollinators are exposed to a wide variety of pesticides.

Wild bee and butterfly samples were collected from the margins of agricultural fields located on five Conservation Areas in Missouri. In 2016 and 2017, samples were collected and composited by genera for a total of 90 samples. Samples were extracted via pressurized liquid extraction and solid phase extraction cleanup. Samples were analyzed for 168 pesticides and degradates using both gas and liquid chromatography-tandem mass spectrometry. Overall, 16 pesticides were detected. Pesticides detected in greater than 2% of the composite samples included: metolachlor (24%), tebuconazole (22%), atrazine (18%), imidacloprid desnitro (13%), bifenthrin (9%), flumetralin (9%), p,p’-DDD (6%), tebupirimfos (4%), fludioxonil (4%), flutriafol (3%), cyproconazole (2%), and oxadiazon (2%). Concentrations for individual pesticides ranged from 2 to 174 ng/g. Results indicate that wild pollinators are exposed to a wide variety of pesticides.

A set of experiments was conducted to determine the dietary clothianidin exposures that cause prepupal mortality in the absence of other adverse effects. Monarch larvae were raised from hatch to pupae on clothianidin contaminated swamp milkweed plants. Larval growth, larval survival, and prepupal survival were monitored throughout the experiments in which the exposures ranged from 1.4 – 2,793.1 ng/g leaf. Exposures of 5.4 – 46.9 ng/g leaf resulted exclusively in prepupal mortality while higher exposures of 1,042.4 – 2,793.1 ng/g leaf resulted exclusively in larval mortality. An LC50 and LC10 of 37 and 6 ng/g, respectively, were estimated based on prepupal mortality.

A set of experiments was conducted to determine the dietary clothianidin exposures that cause prepupal mortality in the absence of other adverse effects. Monarch larvae were raised from hatch to pupae on clothianidin contaminated swamp milkweed plants. Larval growth, larval survival, and prepupal survival were monitored throughout the experiments in which the exposures ranged from 1.4 – 2,793.1 ng/g leaf. Exposures of 5.4 – 46.9 ng/g leaf resulted exclusively in prepupal mortality while higher exposures of 1,042.4 – 2,793.1 ng/g leaf resulted exclusively in larval mortality. An LC50 and LC10 of 37 and 6 ng/g, respectively, were estimated based on prepupal mortality.

Hybrid sunflower production occurs near Sacramento in Northern California where seed treatments are commonly used. In this study, four locations were sampled in 2016 as matched pairs; half of each field was sown with thiamethoxam treated seed and half without. In addition to the thiamethoxam seed treatment, all seeds were coated with two fungicides, fludioxonil and mefenoxam/metalaxyl. Both wild bee and honey bee pesticide exposure was assessed by analyzing field soil, sunflower pollen and nectar, honey bees (pollen and nectar foraging) and a sunflower specialist wild bee, Melissodes agilis. Samples were extracted via pressurized liquid extraction (except nectar which underwent a room temperature solvent extraction) with an organic solvent followed by solid phase extraction cleanup. Samples were analyzed for 168 pesticides and degradates using both gas and liquid chromatography-tandem mass spectrometry. While only one of the three seed coating pesticides (thaimethoxam) was detected, 25 other pesticides and degradates were also measured. In total, 5 insecticides, 9 herbicides, 7 fungicides, and 5 degradates detected across all matrices. There were 7 pesticides and degradates detected in M. agilis, 4 in honey bees, 6 in nectar, 6 in pollen, and 23 in soil. These results indicate the bees visiting sunflower fields are exposed to more pesticides than those used as seed coatings including those pesticides applied to other nearby crops (e.g., rice, tomatoes and walnuts).

Hybrid sunflower production occurs near Sacramento in Northern California where seed treatments are commonly used. In this study, four locations were sampled in 2016 as matched pairs; half of each field was sown with thiamethoxam treated seed and half without. In addition to the thiamethoxam seed treatment, all seeds were coated with two fungicides, fludioxonil and mefenoxam/metalaxyl. Both wild bee and honey bee pesticide exposure was assessed by analyzing field soil, sunflower pollen and nectar, honey bees (pollen and nectar foraging) and a sunflower specialist wild bee, Melissodes agilis. Samples were extracted via pressurized liquid extraction (except nectar which underwent a room temperature solvent extraction) with an organic solvent followed by solid phase extraction cleanup. Samples were analyzed for 168 pesticides and degradates using both gas and liquid chromatography-tandem mass spectrometry. While only one of the three seed coating pesticides (thaimethoxam) was detected, 25 other pesticides and degradates were also measured. In total, 5 insecticides, 9 herbicides, 7 fungicides, and 5 degradates detected across all matrices. There were 7 pesticides and degradates detected in M. agilis, 4 in honey bees, 6 in nectar, 6 in pollen, and 23 in soil. These results indicate the bees visiting sunflower fields are exposed to more pesticides than those used as seed coatings including those pesticides applied to other nearby crops (e.g., rice, tomatoes and walnuts).

This data release includes sampling location, pesticide concentrations in passive samplers (silicone bands) and bees foraging in Conservation Reserve Program fields. Sampling took place during July and August of 2019. Fields were located on private land managed for the U.S. Department of Agriculture Conservation Reserve Program in eastern central Iowa, U.S.A. First posted - December 14, 2022(available from author) Revised - October 2023 (version 2.0)

This data release includes sampling location, pesticide concentrations in passive samplers (silicone bands) and bees foraging in Conservation Reserve Program fields. Sampling took place during July and August of 2019. Fields were located on private land managed for the U.S. Department of Agriculture Conservation Reserve Program in eastern central Iowa, U.S.A. First posted - December 14, 2022(available from author) Revised - October 2023 (version 2.0)

Recent concern for the adverse effects from neonicotinoid insecticides has centered on risk for insect pollinators in general and bees specifically. However, natural resource managers are also concerned about the risk of neonicotinoids to conservation efforts for the monarch butterfly (Danaus plexippus) and need additional data to help estimate risk for wild monarch butterflies exposed to those insecticides. In the present study, monarch butterfly larvae were exposed in the laboratory to clothianidin via contaminated milkweed plants from hatch until pupation, and the effects upon larval survival, larval growth, pupation success, and adult size were measured. Soils dosed with a granular insecticide product led to mean clothianidin concentrations of 10.8 – 2193 ng/g in milkweed leaves and 5.8 – 58.0 ng/g in larvae. Treatment of soils also led to clothianidin concentrations of 2.6 – 5.1 ng/g in adult butterflies indicating potential for transfer of systemic insecticides from the soil through plants and larvae to adult butterflies. Estimated LC50s for total mortality (combined mortality of larvae and pupae) and EC50 for larval growth were variable but higher than the majority of concentrations reported in the literature for clothianidin contamination of leaves.