Persistence of cattle grubs (Diptera: Oestridae) on a Canadian ranch with long-term, continuous therapeutic control.

Sero-prevalence of cattle grubs (Diptera: Oestridae) was monitored on two large western Canadian ranches from 1992 to 1999. One ranch has had a long-term programme for therapeutic control of cattle grubs as required by legislation in the province of Alberta. The other ranch, located in southeast Saskatchewan, has not used any treatment for grub control for an extended period of time. Serum from calves was tested each fall for the presence of antibodies to Hypoderma spp. using an ELISA. Percent positive sera on the Ranch 1 ranged from 8.0 to 73.3%. There was substantial variation among years and among two separate herds maintained on the ranch. Percent infested calves on the Ranch 2 ranged from 76.5 to 99.0%. Improved surveillance for cattle grubs using serological techniques is the only effective means to monitor the status of this important parasite.