During the migration of the 3rd instar nymph across the neck and body of the animal, the nymph will climb onto horn flies and other flies and be carried to another animal, thus spreading between animals and herds. Cattle tail-lice may be carried into a herd by the addition of an infested animal. It is desirable to inspect cattle for lice before purchase or as they are handled for branding, vaccination, or other purposes. Most of the insecticides registered by the government for lice control on beef cattle are designed to kill the feeding nymphs and adults, not the eggs. However, because of the environmental influence on egg-hatching time, certain times of the year are more preferable for treatment.
Warm weather allows for rapid egg-hatching.
Hence, re-treatment would be necessary. In general, early spring treatment will control the newly hatched nymphs from the over-winter buildup of eggs as well as aid in controlling horn flies. Proper fall treatments will reduce the nymph and adult populations, thus preventing a winter build-up of eggs. A common practice in Florida is to apply an insecticide pour-on and to dip the tail in diesel fuel to kill the eggs. This practice has been work quite successfully, my only suggestion is to use this technique during cool or cold weather.