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Castro Janer EA. Resistance of Rhipicephalus (Boophilus) microplus (ACARI: IXODIDAE) to fipronil: standardization of in vitro bioassays, detection of resistance in field populations and evaluation of cross-resistance with other drugs. [Ph.D. thesis (Philosofic Doctor in Sciences)]. São Paulo (Brasil): Instituto de Ciências Biomédicas da Universidade de São Paulo; 2010. Rhipicephalus (Boophilus) microplus is one of the main pests of cattle. The losses caused by this tick can be minimized by the use of acaricides. The arthropod, however, has developed resistance to most of them, constituting serious problem in control programs. For the success of management strategies is necessary to use practical tests, economical, fast and reliable that can detect the presence of resistant phenotypes in a population. Fipronil is a relatively new acaricide for use in cattle and there have been no standardized in vitro tests for the diagnosis of tick resistance. This study aimed to standardize in vitro bioassays for diagnosis of resistance to fipronil for their application in the detection of resistance in field populations (Brazil and Uruguay), in studies involving detoxification enzymes in the mechanism of resistance and on the occurrence of cross-resistance to other drugs (ivermectin, lindane). Assays were performed in triplicate for standardization of Adult Immersion Test (AIT, n = 26), Larval Immersion Test (LIT, n = 71) and Larval Packet Test (LPT, n = 41), using the strains susceptible (Mozo) and resistant to fipronil. AIT discriminated the populations in four variables: mortality, egg weight at 7 and 14 days, fertility index and fecundity index. For the tests with larvae the concentrationmortality curves were analyzed. The AIT and LIT were more sensitive than LPT, with higher resistance ratios (RR). The discriminating concentrations (DC) (2xCL99,9) for mortality in trials using AIT, LIT and LPT were: 4.98, 7.64 and 2365.8 ppm with strain Mozo. The RR of the resistant population were 202.4, 5.36 and 1.52. The tests were validated with field populations of Brazil (38) and Uruguay (28) derived, respectively, from ranches of milk and beef cattle. The use of LIT, allowed the early diagnosis of in vitro resistance to fipronil (RR≥2) in populations of cattle ticks in Brazil (19) and Uruguay (5), beside others with incipient resistance. In Uruguay, the resistant populations are limited to a mainly agricultural region where the use of endosulfan and fipronil in the cultures was intense. Ticks from Brazilian ranches that never used fipronil in animals, but that applied it to control termites, were resistant (LIT). Although the evidence is indirect, it appears that the control of agricultural pests can interfere in tick control. The DC currently stipulated was effective because in its use, all the resistant populations tested presented survivors. Metabolic resistance was assessed by use of enzymatic inhibitors: piperonyl butoxide (PBO), triphenylphosphate (TPP) and diethylmaleate (DEM). It was not detected significant drug synergism with PBO and TPP. Possibly the mechanism of resistance could be the target-site insensitivity determined by a mutation Rdl-type since, from 17 populations resistant to fipronil, 14 were resistant to lindane. It was not observed crossresistance with IVM (n = 29). Resistance to IVM in Uruguay is still incipient.

Resistência de Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) a fipronil: Padronização de bioensaios in vitro, detecção de resistência em populações de campo e avaliação sobre resistência cruzada com outras drogas.