Studies on the Mode of Action of Synergized Bayer 21/199 and Its Corresponding Phosphate in the House Fly12

Abstract

The toxicity and the in vitro and in vivo anticholinesterase activity of Bayer 21/199, more recently called Co-Ral® (O-(3-chloro 4-methylumbelliferone) O,O-diethyl phosphorothioate), and its corresponding phosphate, with and without piperonyl butoxide, have been studied in the house fly (Musca domestica L.). Bayer 21/199 and its corresponding phosphate were isotoxic when administered topically to flies. Both compounds were approximately 2.8 times more toxic when administered jointly with piperonyl butoxide. The phosphate of 21/199 was a 435 times more potent anticholinesterase agent in vitro. No increase in inhibition was found with the addition of piperonyl butoxide in vitro but this compound markedly synergized the anticholinesterase activity of 21/199 in vivo. Bayer 21/199 apparently was converted to its corresponding phosphate in vivo and pipcronyl butoxide did not appear to be associated with its oxidative metabolism. A reversibility in cholinesterase inhibition occurred in flies treated with 21/199 with or without piperonyl butoxide.