Acaricides resistance in Rhipicephalus microplus and expression profile of ABC-transporter genes in the sampled populations.

Currently, livestock owners manage tick infestations using chemicals, but the method is increasingly losing effectiveness as resistant tick populations have established in the field conditions. Thus, to develop effective tick management strategies, monitoring of resistance in most predominant tick species, Rhipicephalus microplus was targeted. The ticks were collected from eleven districts of Madhya Pradesh and one district of Punjab and tested against deltamethrin (DLM), cypermethrin (CYP), coumaphos (CMP), ivermectin (IVM) and fipronil (FIP), through adult immersion and larval packet tests. The field isolates were highly resistant to DLM [Resistance factor (RF) = 3.98-38.84]. Against CYP, resistance was observed in BWN (Barwani; RF = 2.81) and MND (Mandsaur; RF = 3.23) isolates. Surprisingly, most of the isolates were susceptible to CMP (0.34-1.58). Emerging level of resistance against IVM (1.05-4.98) and FIP (0.40-2.18) was also observed in all the isolates. Significantly elevated production of esterases (p < 0.01) was 90% correlated with RF of DLM while no positive correlation between production of monooxygenase and Glutathione S-transferase with RF to DLM was noted. Multiple sequence analysis of S4-5 linker region of the sodium channel gene of all the isolates revealed a point mutation at 190th position (C190A) which is associated with DLM resistance. Treatment of resistant LDH (Ludhiana) isolate with IVM resulted in upregulation of RmABCC2 gene and insignificant upregulation of RmABCC1 and RmABCB10 genes indicating the probability of linking IVM resistance with over-expression of RmABCC2 gene. The possible tick management strategies are discussed.