Acaricide resistance in Boophilus microplus ticks collected from two ecological Zones of Khyber Pakhtunkhwa, Pakistan

Boophilus microplus is a major cattle tick specie causing great economic loss to the dairy industry throughout the globe including Pakistan. Trichlorfon and Deltamethrin are used to control bovine ticks, and their sprays are also used in other pest control programs that exert pressure on ticks to gain resistance. This study is aimed to examine the resistance level of Rhipiciphalus microplus against trichlorfon and deltamethrin. The engorged ticks were collected from two ecological regions of Khyber Pakhtunkhwa, KPK Pakistan i.e., Swat & Dir (zone-1), and Charsadda & Nowshera (zone-2). Four concentrations of acaricides in two-fold and ten-fold ppm with three replicates for each were used in both bioassays. Egg hatch assay and adult immersion tests were used to assess the resistance status. The probit analysis of egg hatch assay showed the highest hatching percentage in zone 1 on both dilutions (67-76% on two-fold and 68-88% on ten-fold dilution) while lethal concentration (LC95) was found to be 2.187 ppm and discriminating dose (DD) as 4.374 ppm for trichlorfon. In zone 2, hatching percentage was 73-84 on two-fold and 72-91% on ten-fold dilution while LC95 was recorded as 0.599 ppm and DD as 1.198 ppm. The same parameters were studied for deltamethrin and in zone 1 the hatching percentage was found as 38-56% on two-fold dilution and 37-80% on ten-fold dilution while LC95 was recorded as 0.001 ppm and DD as 0.002 ppm. In zone 2, the hatchability was recorded as 42-58% on two-fold and 43-85% on ten-fold dilution. The values for LC95 was recorded as 0.001 ppm and DD as 0.002 ppm. Further, analysis of adult immersion test against trichlorfon revealed the values of LC50 as 2.85 ppm and LC95 as 4.71 ppm in zone 1 and in zone 2 as 3.14 ppm and 5.28 ppm, respectively. Similarly, LC50 and LC95 against deltamethrin was recorded as 0.79 ppm & 1.71 ppm in zone 1 and 0.45 ppm & 4.325 ppm in zone 2, respectively. Based on the findings of this study, the isolated Rhipicephalus microplus was found to be more resistant to the widely used acaricides i.e., trichlorfon than deltamethrin. In order to maintain the efficacy of acaricides at country level, the study recommends continuous monitoring of resistance.

Insecticide susceptibility status and major detoxifying enzymes activity in Anopheles subpictus from Kasur, Pakistan

Anopheles subpictus s.l. Grassi (Diptera: Culicidae) is a malaria vector in South Asia, where insecticides are the mainstay for vector control interventions. Information on any variation in metabolic enzyme levels in mosquitoes is helpful with respect to adapting alternative strategies for vector control. The scarce data on the biochemical basis of insecticide resistance in malaria vectors of Pakistan limit the available information for vector control interventions within the country. The insecticide susceptibility status and its biochemical basis against dichlorodiphenyltrichloroethane (DDT) (4%), deltamethrin (0.05%) and permethrin (0.75%) in An. subpictus s.l. collected from all Tehsils of district Kasur were evaluated. For this purpose, a World Health Organization susceptibility bioassay was performed followed by the detection of altered metabolic enzyme activity using biochemical assays. Similarly, a significant difference in knock-down effect was observed among field collected and susceptible strain against all insecticides 24 h post exposure. The overall mean mortality rates of DDT, deltamethrin and permethrin were 27.86% [95% confidence interval (CI) = 29.65-26.06], 44.89% (95% CI = 46.23-43.54) and 78.82% (95% CI = 80.16-77.47), respectively. The biochemical assays revealed an elevated level of metabolic enzymes in the field population. The results provide evidence of resistance against organochlorine and pyrethroid groups in a field population of An. subpictus s.l. from district Kasur mediated by multiple metabolic mechanisms, including acetylcholinesterases, esterases, cytochrome P450 and glutathione S-transferases.