Toxilogical effects and resistance to pyrethroids in Boophilus micropuls from Goiás, Brazil

RESUMO

In order to monitor the susceptibility of Boophilus microplus to acaricides and improve control measures, the effects of cypermethrin, deltamethrin on larvae obtained in the city of Goiânia in the Brazilian state of Goiás were studied. Although these pyrethroids are already sold as acaricides, their cost-benefit efficiency has been questioned. Fasting 14-21 day-old larvae were immersed in solutions of the acaricides under test, maintained at 27+/-§C, and relative humidity over 80 per cent, and observed under the stereoscope within an apparatus ariginally designed for studying the non-parasitic phase of the tick life cycle. The observed toxicological effects were excitability, repetitive motion, decreased motor ability, detachment, paralysis, knock-down and cuticular proliferation of liquids and gases. The materials used in the manufacture of this apparatus consisted of disposable Petri dishes, "organza" cloth and paraffin, none of which are toxic to tick larvae. Mean death rates after 24h were 76.3 per cent, 87.5 per cent, 77.6 per cent, 91.2 per cent, 86.2 per cent and 100 per cent for 25 and 50ppm deltamethrin, 150 and 300ppm cypermethrin and 1250 and 2500ppm permethrin, respectively. The ticks were resistant to commercial concentrations of deltamethrin and cypermethrin. Only 2500ppm permethrin produced the mortality recommended by the Brazilian Ministry of Agriculture