Evaluation of cytotoxic effects of amitraz and fipronil on digestive, reproductive and neural processes of engorged Rhipicephalus microplus (Acari: Ixodidae) female

Fipronil and amitraz are potentially toxic compounds used for controlling ticks infesting pet and livestock. The use of fipronil on large animals was limited because of its high costs while amitraz is still persisting in the market since its introduction over four decades ago. Though resistance in ticks against these pesticides has been reported worldwide since 2000, the toxicity of these chemicals at cellular level in ticks is still poorly understood. The present study aimed to examine the gross and cellular impact of fipronil and amitraz on the gut, ovaries and synganglion of engorged Rhipicephalus microplus females. Fipronil and amitraz treated tick groups showed formation of a large number of vacuoles of different size throughout the cytoplasm of generative cells whereas sessile, residual and detached digestive cells were very low in numbers. The treatment of ticks resulted in the formation of vacuolations at periphery of all oocytes. Ultra-thin sections of the synganglion revealed severe rupture of neural lamella and perineurium with apoptosis of neural cells after fipronil treatment whereas in the amitraz treated ticks, severe destruction of neuropile region and extensive vacuolation of type I and II cells of cortical region as compared to the unexposed ticks were noted.