Potential impacts of climate variation on the American burying beetle, Nicrophorus americanus Oliver: Overwintering, voltinism, and phoretic mites

The American burying beetle (ABB), Nicrophorus americanus Oliver, is North America’s largest burying beetle. This species is a habitat generalist that uses small carrion to feed and breed. ABB has been lost from nearly 90% of its range and was classified as federally threatened in 2020. Research on its population decline continues, but its response to climate change, overwintering survival, and reproduction are understudied. Population surveys were conducted for ten Silphinae species including ABB in Oklahoma at Camp Gruber Military Reserve (Muskogee County) and the Tallgrass Prairie Preserve (Osage County). Results demonstrated a decline in species presence from 2023 to 2024 and an overall lower number of beetles present in Osage County compared to Muskogee County. Data showed ABB to favor grassland habitats in Muskogee County and savannah habitats in Osage County. Using laboratory bred beetles, the mean (±S.E.) lethal maximum temperature of ABB was determined to be 35.85°C (±0.68) when exposed to continuous increase of temperature. When beetles were exposed to temperature increases at 10-minute periods, average lethal maximum was increased to 37.78°C (±0.17). Overwintering trials were conducted on ABB in Stillwater, Oklahoma where a decline in beetle survival was observed in second-year trials. To better understand why this may have occurred, the supercooling point (SCP) of ABB was determined where the average was -1.98°C (±0.2). Differences in precipitation rather than temperatures appear to explain the differences between years in both summer populations and overwinter survival. Finally, the relationship of burying beetles and their phoretic mites that can become overcrowded, especially after breeding, was determined. Lethal maximum temperature for mites without their host beetles at a constant increase with 10-minute intervals was 36.9°C (±0.15) and was lower at 34.5°C (±0.33) with a constant temperature increase. Mites at densities greater than 200 per beetle left their host at 33.64°C (±0.47). This suggests that beetles can reduce mite loads by increasing their temperatures. The results of these experiments highlight reduction in populations during drought, lowered overwinter survival under dry conditions, and a mechanism to reduce mite load by increasing body temperature.