Widespread exposure to neonicotinoid insecticide in bobcats (Lynx rufus), fishers (Pekania pennanti), and river otters (Lontra canadensis) in North Dakota, USA

Neonicotinoids are the most widely used class of insecticides and are marketed as being safe for wildlife because of their specificity to the nervous system of invertebrates. However, recent work has found widespread environmental exposure to neonicotinoids for several species, as well as an adverse effect on behavior and survival of captive white-tailed deer (Odocoileus virginianus) and other non-target species. Our objective was to measure imidacloprid in the spleens of three wild mesocarnivore species in North Dakota: bobcats (Lynx rufus), fishers (Pekania pennanti) and river otters (Lontra canadensis). We detected imidacloprid in 13% (n = 112), 15% (n = 100), and 35% (n = 100) of bobcats, fishers, and river otters with respective mean concentrations of 3.25, 4.07, and 3.33 ng/g. Mean imidacloprid concentrations found in spleens of mesocarnivores were nearly 10 times greater than the mean level of imidacloprid in spleens of captive white-tailed deer fawns that died during neonicotinoid experiments and were 5 times greater than in free-ranging deer (0.60 ng/g) in North Dakota. The probability of detecting imidacloprid was related to Julian date and peaked around 18 July for otters. The detection probability in these species increased as they increased their distance from water. Imidacloprid concentration also varied by minor watershed for river otters. Detection probability and imidacloprid concentration was not related to age, sex, Julian date, distance to water, or year for bobcats or fishers. Our findings confirm the presence of imidacloprid in vertebrate species unlikely to have direct contact with treated grain crops. This suggests that the perpetuation or maintenance of imidacloprid within food webs potentially extends well beyond the seasonal agricultural influx. Further research is needed to understand these dynamics, and their impact to animal and environmental health.