Control of Bovicola Equi (Phthiraptera: Trichodectidae) with Dimilin and Permethrin

Authors: Reeves, Will; Miller, Myrna

Submitted to: Journal of Vector Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2009
Publication Date: 6/8/2009
Citation: Reeves, W.K., Miller, M.M. 2009. Control of Bovicola Equi (Phthiraptera: Trichodectidae) with Dimilin and Permethrin. Journal of Vector Ecology. Vol 34: 160.

Interpretive Summary: Lice are wingless ectoparasitic insects that can irritate and injure their hosts and transmit pathogens. Horses and ponies can be infested with a chewing louse that irritates the animals, creates skin lesions, causes hair loss, and generally reduces animal fitness. Chemical control of lice has been accomplished with a wide range of insecticides, but many are no longer available. Dimilin has been shown to be effective in controlling lice on cattle. We report on the insecticidal activity of Clean-UpTM (KMG Chemicals, Houston, TX), a pour-on insecticide containing 5% Dimilin mixed with 5% permethrin in for the control of lice on ponies. Louse infestations were measured on 5 naturally infested ponies. Treatment animals were treated with 3 ml/45 kg of Clean-UpTM as a pour-on along the back-midline. After 6 weeks the ponies were haltered and lice were enumerated as previously described. The average louse infestation for the pre-treatment ponies was 8 lice/182 cm2. Post treatment louse numbers increased on control animals to an average 36 lice/182 cm2 and there were no lice found on treated. Based on our data a mixture of 5% Dimilin with 5% permethrin in an oil based solution will control B. equi.

Technical Abstract: Lice are wingless ectoparasitic insects that can irritate and injure their hosts and transmit pathogens. Horses and ponies can be infested with a chewing louse, Bovicola equi (Denny) (Phthiraptera: Trichodectidae) that irritates the animals, creates skin lesions, causes hair loss, and generally reduces animal fitness. In addition to irritating their hosts some lice of livestock have been associated with pathogens. Chemical control of lice has been accomplished with a wide range of systemic and topical insecticides. Many pesticides used for louse control are no longer available. Benzoylphenylureas such as diflubenzuron (Dimilin) and triflumuron are chitin synthesis inhibitors. Dimilin has been shown to be effective in controlling Bovicola bovis L. on cattle. We report on the insecticidal activity of Clean-UpTM (KMG Chemicals, Houston, TX), a pour-on insecticide containing 5% Dimilin mixed with 5% permethrin in an oil-based solution, for the control of B. equi on naturally infested Shetland ponies. Five Shetland ponies were housed in the laboratory animal facility. These ponies were naturally infested with B. equi. Louse infestations were measured on each animal by counting all lice in a known area. Briefly, ponies were haltered, numbered, and 182 cm2 of hair were sheared with an electric clippers from the flank, midline, and hindquarters. The hair was clipped down to the skin and all hair and clippings were collected in individual plastic bags. The sheared areas were visually checked for lice and if lice were found they were placed in the plastic bags. Ponies were randomly sorted into a control and treatment groups and isolated in pens with no physical contact with other horses. Treatment animals were treated with 3 ml/45 kg of Clean-UpTM as a pour-on along the back-midline. After 6 weeks the ponies were haltered and lice were enumerated as previously described. Animals were sheared on the opposite side. The average louse infestation for the pre-treatment ponies was 8 lice/182 cm2. Post treatment louse numbers increased on control animals to an average 36 lice/182 cm2 and there were no lice found on treated. Based on our data a mixture of 5% Dimilin with 5% permethrin in an oil based solution will control B. equi.