Determination and establishment of discriminating concentrations of malathion, coumaphos, fenvalerate and fipronil for monitoring acaricide resistance in ticks infesting animals

Discriminating concentrations (DCs) of malathion, coumaphos, fenvalerate and fipronil were determined to monitor acaricide resistance in field conditions. The LC99 values with 95% confidence interval for malathion, coumaphos, fenvalerate and fipronil were 5126.8 (5011.5–5240.7), 131.0 (120.4–142.5), 2257.5 (2198.1–2318.4) and 6.2 (5.87–6.55), respectively. The narrow confidence intervals in LC50 and LC99 of adult immersion test (AIT) and larval packet test (LPT) affirming the homogeneity of IVRI-I line. Variation in LPT based LC50 and LC99 values of malathion (55.9 ppm) and coumpahos (28.4 ppm) compared to those obtained in AIT indicating that larvae were more susceptible to these chemicals. The DCs for malathion, coumaphos, fenvalerate and fipronil against adults were determined as 10253.6, 262.0, 4515.0 and 12.4 ppm while against larvae the values were 111.8, 56.8, 4014.0 and 9.6 ppm, respectively. The working efficiency of DCs was successfully tested in field tick isolates. Establishment of country specific DCs of commonly used insecticides for monitoring of resistance in field ticks is emphasized for establishing tick control strategies.