Comparative efficacy of fenthion, dichlorvos/fenitrothion and permethrin against the flea, Ctenocephahdes felis, on the dog

In a series of three replicated and controlled trials, nine dogs artificially infected with Ctenocephalides felis were treated with a systemically active ‘spot-on’ formulation of fenthion, six with a topical spray containing dichlorvos and fenitrothion and six with a surface active ‘spot-on’ preparation containing permethrin, all at recommended dose rates. Good knockdown efficacy was apparent at eight hours with the dichlorvos/fenitrothion combination and at 24 hours with the other formulations. Efficacy values in excess of 95 per cent persisted for at least 22 days in the case of the systemic fenthion preparation and the permethrin product and eight days for the dichlorvos and fenitrothion combination. Twenty-nine days after treatment there was still substantial protection in the fenthion- and permethrin-treated animals, indicated by an 88 and a 77 per cent reduction in flea counts in the two groups, respectively.