Novel mode of action of spinosad: Receptor binding studies demonstrating lack of interaction with known insecticidal target sites

The ability of spinosyn A to either enhance or displace binding to selected insecticidally-relevant receptors was investigated using a number of radioligands including, [H-3]imidacloprid and [H-3]livermectin in tissues from the ventral nerve cord (VNC) membranes of the American cockroach, Periplaneta americana and head membranes from the housefly, Musca domestica. In these insect neural tissues, spinosyn A does not appear to alter the binding of a number of radioligands suggesting that spinosyn A does not interact directly with a variety of known receptors, including nicotinic or gamma-aminobutyric acid (GABA)-based insecticidal target sites. However, available data are consistent with spinosyn A interacting with a site distinct from currently known insecticidal target sites, thus Supporting a novel insecticidal mechanism of action for the spinosyns. (C) 2009 Elsevier Inc. All rights reserved.