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.

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.

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.

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.

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.

Citrated plasma samples were sent to the University of Miami Avian and Wildlife Laboratory for clinical determination of total protein, plasma electrophoresis (pre-albumin, albumin, alpha 1 globulins, alpha 2 globulins, beta globulins, gamma globulins) and aspartate aminotransferase and creatine phosphokinase activities.

Range finding trial in which kestrels were fed diets containing varying quantities of brodifacoum and signs of intoxication were monitored.

Citrated plasma samples were sent to the University of Miami Avian and Wildlife Laboratory for clinical determination of total protein, plasma electrophoresis (pre-albumin, albumin, alpha 1 globulins, alpha 2 globulins, beta globulins, gamma globulins) and aspartate aminotransferase and creatine phosphokinase activities.

- Observations of test subjects, - Body weight - Estimates of test diet consumption - Hematocrit - Clotting time parameters (prothrombin time, Russell’s viper venom time, fibrinogen concentration) - Residues of brodifacoum and chlorophacinone in tissue

- Observations of test subjects, - Body weight - Estimates of test diet consumption - Hematocrit - Clotting time parameters (prothrombin time, Russell’s viper venom time, fibrinogen concentration) - Residues of brodifacoum and chlorophacinone in tissue