Establishment of anti-tick activity of green nano-formulation for the management of acaricide-resistant cattle tick, Rhipicephalus microplus - An in vitro, in vivo and field study.

The increasing incidence of acaricide resistance in Rhipicephalus microplus necessitates development of alternative strategies for control. The present study evaluated the anti-tick efficacy of a green nano-formulation (GNF) against reference acaricide susceptible and resistant strains of R. microplus. Dose-response bioassay against the susceptible IVRI-I strain revealed a concentration dependent increase in mortality and oviposition inhibition with an estimated LC50 and LC95 values of 4.76% and 8.76%, respectively, indicating potent acaricidal activity. Complete egg-laying inhibition was observed at 10% concentration. At 10% concentration 86% of treated pyrethroid-resistant (IVRI-IV) and multi-acaricides resistant (IVRI-V) ticks died within the experimental period. The GNF exhibited 81.5-94.2% mortality with significant oviposition inhibition of 25.1-50.9% against the field isolates resistant to multiple acaricides. Besides adults, a 100% mortality of larvae of susceptible and resistant tick strain and a drastic reduction of hatching percentages of eggs was noted after treatment of tick stages with 10% GNF. Stability studies indicated a consistent efficacy of GNF of >85% up to nine months at varying storage temperatures. Under in vivo conditions, GNF treatment resulted in a immediate mortality of 79.1% ticks used in experimental infestation of animals with significant reduction in engorged female weight, egg masses and subsequent tick emergence. In naturally infested animals, efficacy was >85% in low to moderately infested group after a single application, while repeat treatment eliminated heavy infestations by 10th day. Field trials conducted in Bareilly and Rampur districts further confirmed consistent efficacies of 78.7% and 93.8%, respectively. The findings clearly demonstrated the acaricidal and larvicidal activities of GNF against R. microplus populations resistant to multiple acaricides and have strong potential to use in the field conditions for the management of tick infestations on animals.