Resistance and control of cypermethrin and chlorpyrifos as acaricide for control of hard tick Haemaphysalis longicornis (acari: ixodidae)

Abstract : Chemotherapeutic treatment is still the foundation of tick control programs. This study investigated theacaricidal efficacy of cypermethrin alone and in combination with chlorpyrifos against Haemaphysalis (H.) longicornis.Unfed larval ticks were exposed to 0.1, 1.0, and 10 mg/mL cypermethrin for 60 min, after which the acaricidal efficacywas examined based on tick mortality. All compounds showed similar suppression curves, with the best control beingachieved by cypermethrin and chlorpyrifos (1 : 1 ratio) at 10 mg/mL. Effective cypermethrin concentrations for tickcontrol were two to seven times higher than the recommended doses, indicating resistance by H. longicornis.Keywords : acaricide, Haemaphysalis longicornis, tick control Tick-borne diseases are among the most important vector-borne diseases that cause significant losses to humans as aresult of damage to domestic and wild animals. A number ofdifferent tick control strategies have been used by livestockfarmers and animal practitioners, including grooming [10],genetic manipulation through increasing Bos indicus contentin the progeny [8], biological control in poultry [13], ento-mopathogenic fungi [15], immunological control throughproduction of vaccines against tick species [7], and ethnovet-erinary practices. Ticks transmit several disease pathogens,including Babesia and Theileria parasites, Borrelia bacteria,and the encephalomyelitis virus. To reduce or prevent thesediseases in domestic animals, control of the tick vector isnecessary. Tick monitoring is also important to detect itsearly stage. It helps to reduce the spread resistance and toobtain knowledge of distribution of acaricide resistance.Standard methods are needed to assess resistance evolutionand allow the comparison of resistance data between labora-tories. It is also important to study specific effects of selectedacaricide on specific species. There are a variety of methodsthat have been used to suppress tick vector populations [14];however, chemotherapeutic control remains the foundation oftick control programs for the eradication of livestock infesta-tions in the developing world [2]. A progressive decrease inthe efficiency of acaricidal drugs through the development ofresistance [1] would undermine this method. Epidemiologi-cal investigations have suggested that a reduction in acari-cide-treatment frequency that permits high tick attachmentrates allows for the development of endemic stability [9]. Tothis end, a regular screening of compounds is required todetermination their efficacy. Thus far, various groups of aca-ricides have been found to have significant efficacy for tickcontrol, including pyrethroids [20], avermectins, organophos-phates, organochlorines, carbamates, and insect growth regu-lators. Pyrethroid acaricides have been used for more than 40years and account for 25% of the worldwide acaricide mar-ket [3]. The pyrethroid class of acaricides was derived fromnatural compounds isolated from the Chrysanthemum genusof plants. The primary mode of pyrethroid action in bothinsects and mammals is disruption of voltage-sensitivesodium channel (VSSC) function, and any potential disrup-tor of VSSC function has potent acaricidal or toxicologicalactivity. Often, pyrethroids are sold and/or used as mixturescontaining a combination of two or more compounds. Gener-ally, the pyrethroid acaricide cypermethrin is used in combi-nation with chlorpyrifos. Chlorpyrifos is a toxic crystallineorganophosphate acaricide that inhibits acetylcholinesteraseand is used to control insect pests. The main objectives of this study were to detect the levelsof tick resistance to acaricides, to compare in vitro test meth-ods, and to investigate the lowest concentrations of cyper-methrin alone and cypermethrin in combination with chlorpyrifosfor maximum tick suppression. There is no available dataregarding the effects of these chemical compounds on thehard tick Haemaphysalis (H.) longicornis. We examined effi-