Abstract
In Kuro island of Okinawa Prefecture, to control Boophilus microplus, coumaphos 50% wettable powderhas been used for about sixteen years, and BPMC 20% emulsifiable concentrate for about six months. Recently, in most pastures, control of ticks with these tickicides has become considerably difficult. Thus, susceptibility of unfed larval ticks collected from 7 pastures in the island to one organophosphorus (coumaphos), two carbamates (BPMC and propoxur), and one pyrethroid (flumethrin) was examined in the laboratory using the knockdown method. The KT50 values of coumaphos and two carbamates for the ticks tested were larger than that of a cultured reference tick which is susceptible to several tickicides. On the contrary, KT50 value of flumethrin for ticks tested was smaller than that of a cultured reference tick. According to this result, pyrethroid tickicide was used for tick control in all the pastures. As a result, ticks disappeared completels in all the pastres. Based on these observations, it was suggested that the ticks tested are resistant to the organophosphorus and carbamates tickicides, and the knockdown method is useful for measuring susceptibility of ticks to several tickicides, as well as for choice of effective tickicides.
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