Control of Boophilus ticks on heifers with two pyrethroids applied as sprays.

The pyrethroid permethrin (25% cis to 75% trans) was sprayed on Hereford heifers infested with all parasitic stages of Boophilus microplus (Canestrini) at 0.05% and 0.1% active ingredient. At 0.05%, control was 66.7%; whereas at 0.1%, control was 93.3%. Replete females were collected daily for 28 days after treatment at both concentrations, indicating that at least some ticks treated as larvae or nymphs were able to reach repletion. The pyrethroid fenvalerate was sprayed on Hereford heifers infested with all parasitic stages of B microplus or B annulatus (Say) at 0.025% and 0.05% active ingredient. Fenvalerate was as effective as permethrin at a lower concentration. At 0.025%, control was 89.2% and 86.6% and at 0.05% was 92.5% and 90.1% for B microplus and B annulatus , respectively. Both these pyrethroids could provide adequate reduction in programs in which control is the aim; however, in an eradication program, both acaricides failed to provide the necessary reduction to achieve complete elimination.