Holstein heifers in a confined feedlot setting on a southern California dai
ry were either sprayed individually along the ventral midline using 0.2% pe
rmethrin (250 ml/animal) (two pens) or were not treated (two pens). Treatme
nts (n = 6 dates) were applied every 2 wk during the peak fall bluetongue v
irus transmission season (22 August-29 October). Animals seronegative for b
luetongue virus antibodies at the initial bleeding on 15-18 September (n =
106 in the treatment pens and n = 117 in the control pens) were bled again
for testing 2 mo later (12-13 November). Seroconversion rates were not sign
ificantly different: 56% for the treated animals and 48% for the controls (
P > 0.2). The area has many essentially contiguous confinement dairies with
wastewater ponds that produce large numbers of Culicoides sonorensis Wirth
& Jones, the primary bluetongue virus vector. Further, these dairies presu
mably provided a large reservoir of virus-infected cattle to infect vectors
in the immediate area. Under these severe virus challenge conditions, perm
ethrin applied at 2-wk intervals failed to reduce exposure to bluetongue vi
rus.