Resistance to Cypermethrin Is Widespread in Cattle Ticks (Rhipicephalus microplus) in the Province of Punjab, Pakistan: In Vitro Diagnosis of Acaricide Resistance

Control of the cattle tick Rhipicephalus (R.) microplus mainly relies on chemical acaricides and cypermethrin is the most widely used acaricide in Pakistan. Farmers frequently complain about its low efficacy, thus, the present study was designed to quantify the frequency of cypermethrin resistance in cattle ticks. Engorged female R. microplus were collected and tested for the efficacy of cypermethrin using the FAO-recommended larval packet test. Resistance factors (RF) were estimated at both the lethal concentration for 50% (LC₅₀) and 99% (LC₉₉) of ticks. Thirty-three samples were tested, of which 8/33 (24.24%) were classified as resistant based on the RF₅₀, and all 33 were classified as resistant based on the RF₉₉. In District Sargodha, when only the RF₅₀ was considered, 45.5% of samples were classified as resistant, but at RF₉₉, all tested samples were identified as resistant. In District Okara, the variation in RF₅₀ estimates was 2.2-8.3 and variation in RF₉₉ estimates was 10.6-1139.8. Similar results were found in District Attock, where variations in RF₅₀ were 0.8-8.5 and RF₉₉ ranged from 9-237.3. The study showed that cypermethrin resistance is prevalent in these three districts of Pakistan and is likely to be overestimated by classification based on the RF₉₉.