Toxicity and nicotinic acetylcholine receptor interaction of imidacloprid and its metabolites in Apis mellifera (Hymenoptera: Apidae)

• Published in: Pest management science Vol. 57; no. 7; pp. 577 - 586
• Main Authors: Nauen, Ralf, Ebbinghaus-Kintscher, Ulrich, Schmuck, Richard
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.07.2001; Wiley
• Subjects: acetylcholine receptor; Animal, plant and microbial ecology; Animals; Apidae; Apis mellifera; Applied ecology; Bees - metabolism; Biological and medical sciences; Biological Assay; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on protozoa and invertebrates; Electrophysiology; Fundamental and applied biological sciences. Psychology; imidacloprid; Imidazoles - chemistry; Imidazoles - metabolism; Insecticides - chemistry; Insecticides - metabolism; Lethal Dose 50; nAChR; Neonicotinoids; neurons; Neurons - drug effects; Nicotinic Agonists - pharmacology; Nitro Compounds; Receptors, Nicotinic - metabolism; toxicity; Agonist; Insecticide; Ligand; Metabolite; Toxicity; Insecta; Non target effect; Apidae; Electrophysiology; Binding site; Apis mellifera; Cholinergic receptor; Apoidea; Chemical control; Nicotinic receptor; Aculeata; Nitroguanidine derivatives; Pesticides; Guanidines; Voltage clamp method; Pollinator; Lethal dose 50; Arthropoda; Neurotoxin; Concentration metabolism relation; Acetylcholine; Hymenoptera; Invertebrata; Non target organism
• ISSN: 1526-498X; 1526-4998
• DOI: 10.1002/ps.331

Acute oral and contact toxicity tests of imidacloprid, an insecticide acting agonistically on nicotinic acetylcholine receptors (nAChR), to adult honeybees, Apis mellifera L var carnica, were carried out by seven different European research facilities. Results indicated that the 48‐h oral LD50 of imidacloprid is between 41 and >81 ng per bee, and the contact LD50 between 49 and 102 ng per bee. The ingested amount of imidacloprid‐containing sucrose solution decreased with increasing imidacloprid concentrations and may be attributed to dose‐related sub‐lethal intoxication symptoms or to antifeedant responses. Some previously reported imidacloprid metabolites occuring at low levels in planta after seed dressing, ie olefine‐, 5‐OH‐ and 4,5‐OH‐imidacloprid, showed lower oral LD50 values (>36, >49 and 159 ng per bee, respectively) compared with the concurrently tested parent molecule (41 ng per bee). The urea metabolite and 6‐chloronicotinic acid (6‐CNA) exhibited LD50 values of >99 500 and >121 500 ng per bee, respectively. The pharmacological profile of the [3H]imidacloprid binding site in honeybee head membrane preparations is consistent with that anticipated for a nAChR. IC50 values for the displacement of [3H]imidacloprid by several metabolites such as olefine, 5‐OH‐, 4,5‐OH‐imidacloprid, urea and 6‐CNA were 0.45, 24, 6600, >100 000, and >100 000 nM, respectively. Displacement of [3H]imidacloprid by imidacloprid revealed an IC50 value of 2.9 nM, thus correlating well with the observed acute oral toxicity of the compounds in honeybees. Neurons isolated from the antennal lobe of A mellifera and subjected to whole‐cell voltage clamp electrophysiology responded to the application of 100 µM acetylcholine with a fast inward current of between 30 and 1600 pA at −70 mV clamp potential. Imidacloprid and two of the metabolites (olefine‐ and 5‐OH‐imidacloprid) acted agonistically on these neurons, whereas the others did not induce currents at test conencentrations up to 3 mM. The electrophysiological data revealed Hill coefficients of approximately 1, indicating a single binding site responsible for an activation of the receptor and no direct cooperativity or allosteric interaction with a second binding site. © 2001 Society of Chemical Industry