Toxicological Studies on Dichlorvos Feed-Additive Formulations to Control House Flies and Face Flies in Cattle Feces1

Abstract

Polyvinyl chloride resin formulations of dichlorvos (DDVP) designed for rapid release (XP-515) and slow release (XP-602) were tested for efficacy in controlling house fly, Musca domestica L., larvae, in manure when mixed in cattle feed for 33 and 32 days, respectively. Bioassays of manure from cattle receiving the feed formulations at 0.5, 1.0, 2.0, and 1.0 mg/kg per day exhibited excellent fly control. Blood cholinesterase levels of animals receiving XP-515 showed no depression at 0.5 and 1.0 mg/kg level but a significant depression occurred at 2.0 and 4.0 mg/kg. XP-602 caused no depression at 0.5 mg/kg but significant depressions at 1.0, 2.0 and 4.0 mg/kg levels. Weight gains, feed consumption, palatability, and feed conversion were generally unaffected. No clinical signs of toxicity to cattle were observed and no gross pathological changes were evident. The comparative toxicity of dichlorvos to larvae of the house fly and face fly, M. autumnalis DeGeer, was studied by mixing purified dichlorvos in bovine manure before implanting it with newly hatched larvae. Face fly larvae were approximately twice as susceptible as house fly larvae with LD60’s of 0.013 and 0.028 µg/gm, respectively. In view of the greater susceptibility of the face fly to dichlorvos in manure, the PVC resin formulations would be expected to control both species at the dosage levels tested.