Residual activity of selected pesticides on laying hens treated for northern fowl mite control by dipping.

Aqueous suspensions of malathion, stirofos, Ravap, and carbaryl formulations (.25 to 1.0%) were tested as dips for control of the northern fowl mite (NFM), Ornithonyssus sylviarum (Canestrini and Fanzago), on caged White Leghorn hens. Hens treated with Ravap showed symptoms of organophosphorus insecticide poisoning soon after treatment and some died as a result of the dip; however, dipping with the other insecticides did not result in any apparent toxic effects. Malathion gave residual control of mites for about 4 weeks posttreatment, but both stirofos and carbaryl dips gave complete control for at least 6 weeks against repeated challenges with the NFM. There were no significant differences in the percent hen-day egg production, feed consumption, or body weight of the hens that could be attributed to any of the chemical treatments.