Effects of 2 Neonicotinoid Insecticides on Blood Cell Profiles and Corticosterone Concentrations of Wood Frogs ( Lithobates sylvaticus )

Abstract

Neonicotinoids are widely used insecticides that are detectable in agricultural waterways. These insecticides are of concern due to their potential impacts on nontarget organisms. Pesticides can affect development of amphibians and suppress the immune system, which could impact disease susceptibility and tolerance. No previous studies on amphibians have examined the effects of these insecticides on differential blood cell proportions or concentrations of corticosterone (a general stress hormone). We investigated the effects of chronic exposure to 2 neonicotinoids, thiamethoxam and clothianidin, on immunometrics of wood frogs (Lithobates sylvaticus). Frogs were exposed to single, chronic treatments of 2.5 or 250 µg/L of clothianidin or thiamethoxam for 7 wk from Gosner stages 25 to 46. The juvenile frogs were then maintained for 3 wk post metamorphosis without exposure to neonicotinoids. We measured water‐borne corticosterone twice: at 6 d and 8 wk after exposure in larval and juvenile frogs, respectively. We assessed differential blood cell profiles from juvenile frogs. Corticosterone was significantly lower in tadpoles exposed to 250 µg/L of thiamethoxam compared with other tadpole treatments, but no significant differences in corticosterone concentrations were found in treatments using juvenile frogs. Anemia was detected in all treatments compared with controls with the exception of tadpoles exposed to 2.5 µg/L of clothianidin. Neutrophil‐to‐leukocyte and neutrophil‐to‐lymphocyte ratios were elevated in frogs exposed to 250 µg/L of thiamethoxam. Collectively, these results indicate that chronic exposure to neonicotinoids has varied impacts on blood cell profiles and corticosterone concentrations of developing wood frogs, which are indicative of stress. Future studies should investigate whether exposure to neonicotinoids increases susceptibility to infection by parasites in both larval and adult wood frogs. Environ Toxicol Chem 2019;38:1273–1284. © 2019 Crown in the right of Canada. Published by Wiley Periodicals Inc. on behalf of SETAC.

Neonicotinoid pesticides exert metabolic effects on avian pollinators

“…Studies using techniques which require additional animal handling have identified cell-mediated immune suppressive effects of neonicotinoid exposure on birds 34 . This immune suppression in vertebrates is thought to be related to elevated levels of stress hormones including corticosterone 39 . Future studies should include periods of more than 3 d between treatment with neonicotinoids and tissue collection to allow for adequate turnover of lymphocytes 54 .…”

“…We used heterophil/lymphocyte ratios as a biomarker of stress-induced suppression of the humoral immune response for its advantages as a low cost, low sample volume, and relatively time-insensitive technique for measuring stress in birds 38 . We predicted that birds would exhibit an increase in heterophil/lymphocyte ratios, a result that has been observed in vertebrates exposed to neonicotinoids 39 . We also performed cholinesterase activity assays to test for effects of short-term, sub-lethal imidacloprid exposure on the cholinergic system of hummingbirds.…”

Association between Haematological Parameters and Exposure to a Mixture of Organophosphate and Neonicotinoid Insecticides among Male Farmworkers in Northern Thailand

“…Based on these findings, we hypothesized that exposure to CLO can cause kidney injury in the same manner as THX, leading to less secretion of EPO and consequently less production of Hb in RBCs. Although limited human studies have reported data, a few animal studies provided evidence that NEOs affect blood cell profiles [23]. For instance, Ghaffar et al found that the levels of RBCs and Hb decreased after exposure to THX in fresh-water fish, suggesting that poor efficiency of fresh-water fish to deliver enough amount of oxygen to other tissues [73].…”

“…Currently, the most sensitive biomarkers of NEO exposure are urinary concentrations of NEO and their specific metabolites such as N-desmethyl-acetamiprid (N-dm-ACE), a metabolite of ACE, desmethyl-clothianidin (dm-CLO), a metabolite of CLO, imidacloprid-olefin (Of-IMI), a metabolite of IMI and thiacloprid-amide (THI-AM), a metabolite of THI [17,18,[20][21][22]. A few animal studies have shown that exposure to NEOs can affect the blood profile and immune system [23,24].…”

Stream Salamander and Benthic Macroinvertebrate Community Responses to Imidacloprid Exposure

“…For example, larval western tiger salamanders (Ambystoma mavortium) had higher corticosterone levels in agricultural wetlands with elevated levels of neonicotinoid insecticides, compared to reference wetlands(Davis et al In Press). In contrast, wood frog (Lithobates sylvaticus) tadpoles experimentally exposed to environmentally relevant concentrations of the neonicotinoid thiamethoxam had lower corticosterone concentrations, and there was no difference in corticosterone concentrations in juveniles(Gavel et al 2019). Male African clawed frogs (Xenopus laevis) had elevated corticosterone concentrations when exposed to the pesticide concoction(Hayes et al 2006).…”