Comparative study on the effects of three insecticides (fipronil, imidacloprid, selamectin) on developmental stages of the cat flea (Ctenocephalides felis Bouche 1835): a light and electron microscopic analysis of in vivo and in vitro experiments

The effects of three insecticides (fipronil, imidacloprid and selamectin) o n developmental stages of cat fleas (Ctenocephalides felis) were studied in vivo, in vitro and by means of light and electron microscopy. The results were documented by video. Adult fleas were attached to the skin of dogs tha t had been treated 7 days before with one of the three compounds. Furthermo re, adult fleas were exposed exclusively to the hair and skin debris of suc h treated dogs or were placed on filter papers that had been impregnated wi th one of these three compounds or with the blood of treated dogs. Larval f leas were exposed to hair of treated dogs, to debris obtained by combing tr eated dogs, to dried blood samples of treated dogs or were placed onto filt er papers impregnated with one of the three compounds. In these experiments with adult and larval fleas, it was noted that none of the three insectici des had a repellent effect on adult or larval fleas. Imidacloprid was the o nly compound that acted exclusively by body contact, and was apparently tak en up by adult and larval fleas via the thin, non-sclerotized intersegmenta l membranes of the flea's body, shown when flea stages were exposed to hair s taken from dogs treated with one of the compounds or placed onto drug-imp regnated filter papers. Imidacloprid killed larvae and adult fleas within 1 h, while it took at least 24 h until all adult fleas had died on fipronil- or selamectin-treated dogs, thus allowing longer feeding periods, increasi ng the risk of transmission of flea-derived diseases. Flea larvae covered w ith debris from dogs topically treated 7 days before with fipronil, imidacl oprid or selamectin died. like the untreated control, within 16-28 h after exposure. This was, however, probably mainly due to a drying effect. Adult and larval fleas exposed to filter papers impregnated with the blood of tre ated dogs survived longer than 7 days, as did the untreated controls. All t hree drugs apparently acted on nerves and muscles and thus stopped motility .