Studies on the Mode of Action of Spinosad: The Internal Effective Concentration and the Concentration Dependence of Neural Excitation

• Published in: Pesticide biochemistry and physiology Vol. 60; no. 2; pp. 103 - 110
• Main Authors: Salgado, Vincent L., Sheets, Joel J., Watson, Gerald B., Schmidt, Arthur L.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01.07.1998; Elsevier
• Subjects: Agronomy. Soil science and plant productions; BIOASSAYS; Biological and medical sciences; CENTRAL NERVOUS SYSTEM; Chemical control; Control; ENSAYO BIOLOGICO; Fundamental and applied biological sciences. Psychology; Generalities. Biometrics, experimentation. Remote sensing; Generalities. Information. Documentation. Research; INSECTICIDAL PROPERTIES; INSECTICIDAS; INSECTICIDE; insecticide mode of action; INSECTICIDES; MANDUCA SEXTA; Medically important nuisances and vectors, pests of stored products and materials: population survey and control; MUSCA DOMESTICA; NEUROTOXICITY; Nuisances; PERIPLANETA AMERICANA; Phytopathology. Animal pests. Plant and forest protection; Protozoa. Invertebrates; radiotracer; SISTEMA NERVIOSO CENTRAL; spinosad; spinosoid; spinosyn; SPINOSYNS; SYSTEME NERVEUX CENTRAL; TEST BIOLOGIQUE; tobacco hornworm; TOXICIDAD; TOXICITE; TOXICITY; Tracer Naturalyte insect control; spinosoid; radiotracer; spinosad; spinosyn; Tracer Naturalyte insect control; insecticide mode of action; tobacco hornworm; Muscidae; Insecticide; Entomology; Insecta; Central nervous system; Electrophysiology; naturalytes; Radioactive tracers; Sphingidae; Ganglion; Macrocycle; Blattidae; Periplaneta americana; Activity concentration relation; Excitation; Mechanism of action; Dictyoptera; Labelled compound; Phytopharmacology; Musca domestica; spinosoids; Pesticides; Lactone; Natural compound; Experimental study; Biological activity; Neurophysiology; spinosyn A; Microbial origin; Larva; Arthropoda; Lepidoptera; Concentration effect; Manduca sexta; Poisoning; Invertebrata; Diptera
• ISSN: 0048-3575; 1095-9939
• DOI: 10.1006/pest.1998.2333

This is the second in a series of reports that define the mode of action of spinosyns, a novel class of naturally derived insecticidal macrocyclic lactones. The concentration dependence of central nervous system (CNS) stimulation was determined using ganglia isolated from cockroaches, house fly larvae, and tobacco hornworm larvae. The tobacco hornworm nervous system was most sensitive, with a steep dose-response relation and an ED50of 5 nM for spinosyn A. The response of the housefly CNS was comparable, showing no clear effect at 3 nM and near-maximal stimulation at 10 nM spinosyn A. The cockroach CNS also displayed a steep dose-response relation, with a threshold of 10 nM and an EC50of 32 nM. That the nerve cords of cockroaches are exposed to comparable levels of spinosyn A during poisoning was established by comparison of the concentration of spinosyn A taken up by cockroach nerve cords during exposurein vivo,in cockroaches treated with a threshold dose, with that in isolated nerve cords equilibrated with a solution of spinosyn A in saline. A saline concentration of 21 nM was estimated to give the same nerve cord concentration as found at the threshold dose for prostration. We can conclude that during poisoning, spinosyn A reaches a concentration inside the insect that is sufficient to directly excite the central nervous system.