Deltamethrin and cypermethrin resistance status of Rhipicephalus (Boophilus) microplus collected from six agro-climatic regions of India

Exploring the relationship between flumethrin resistance and Anaplasma marginale infection in Rhipicephalus (Boophilus) microplus ticks of cattle

The study explores the relationship between flumethrin resistance and Anaplasma marginale infection in Rhipicephalus (Boophilus) microplus of cattle in South Gujarat, India. Adult Immersion Test (AIT) was used to assess flumethrin resistance and polymerase chain reaction (PCR) to confirm A. marginale infection. Species-specific PCR resulted in the amplification of 576 bp of msp5 gene of A. marginale in 17.69% (49/277) groups of ticks, and subsequent digestion with EcoRI cleaved it into two distinct segments. Navsari district, noted level Ι resistance [resistance factors (RF) = 1.78-3.34], and A. marginale prevalence was 16.67, 15.38, 23.08, 15.38, and 11.76% in Navsari, Jalalpore, Gandevi, Chikhli, and Vansda sub-districts, respectively. Similarly, Vyara and Dolvan sub-districts of Tapi observed level Ι resistance (RF = 1-3.63), with A. marginale positivity of 21.43 and 22.22%, while Valod and Songhad demonstrated susceptibility, with 14.29 and 12.50% of A. marginale, respectively. Moving to Surat, the Mahuva, Bardoli, Mandvi, Palsana, and Kamrej sub-districts observed the level Ι resistance (RF = 1.94-2.89), coupled with 14.29, 17.65, 20, 20, and 21.43% of A. marginale, respectively. Lastly, in Valsad district, Dharampur, Kaparada, Valsad, and Umbergaon noted level Ι resistance (RF = 1.67-1.81), and corresponding A. marginale positivity rates of 18.18, 19.23, 15.00, and 20.00%. The scatter plot unveiled a significant moderate positive correlation between RF and A. marginale positivity% (p = 0.0362), characterized by a Pearson correlation coefficient (r) of 0.4963. The covariance (1.1814) highlighted fluctuations, while the coefficient of determination (r2) (0.2463) clarified that 24.63% of the variability in A. marginale positivity% could be attributed to the RF.

Efficacy of hydroethanolic extract of Randia aculeata seed against the southern cattle tick Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) on naturally infested cattle under field conditions

The cattle tick Rhipicephalus (Boophilus) microplus is a major problem of concern for cattle industry in tropical and subtropical areas. Control of cattle tick is based mainly on the use of chemical acaricides, which has contributed to the emerging problem of selection of resistant tick lineages. Plants have been used as an alternative to conventional acaricidal drugs. On the other hand, the acaricidal activity of hydroethanolic extract of Randia aculeata seed (EHRA) has been demonstrated against R. microplus under laboratory conditions. However, the utility of EHRA seed as a potential acaricidal needs to be determined under field conditions. For this reason, the aim of this study was to evaluate the efficacy of the EHRA against R. microplus sprayed on naturally infested calves, determine the effect of the EHRA seed on acetylcholinesterase activity in R. microplus larval and identify the chemical composition of EHRA. Forty-five male calves were divided in three groups and treated with: G1 water; G2 EHRA 20% w/v and G3 coumaphos 0.2% v/v. Acetylcholinesterase (AChE) activity in R. microplus larvae was determined by a colorimetric assay. The chemical composition of EHRA was accessed through HPLC/MS. Significantly fewer ticks were observed after 24 h on the treated group compared to control group. EHRA significantly inhibited in vitro AChE activity in R. microplus at all tested concentrations. Chlorogenic acid, vanillinic acid, p-coumaric acid, caffeic acid. rutin, quercetin, (-)-epicatechin, 4-hydroxybenzoic acid, quercetin, vanillin, 2,4-dimethoxy-6-methylbenzoic acid, scopoletin and ferulic acid were identified in the extract. The results provided new data for the elucidation of the mechanisms of EHRA acaricide action and to further evaluate the use as a new alternative control agent against R. microplus under in vivo conditions.

Acaricides resistance in Rhipicephalus microplus and expression profile of ABC-transporter genes in the sampled populations

Currently, livestock owners manage tick infestations using chemicals, but the method is increasingly losing effectiveness as resistant tick populations have established in the field conditions. Thus, to develop effective tick management strategies, monitoring of resistance in most predominant tick species, Rhipicephalus microplus was targeted. The ticks were collected from eleven districts of Madhya Pradesh and one district of Punjab and tested against deltamethrin (DLM), cypermethrin (CYP), coumaphos (CMP), ivermectin (IVM) and fipronil (FIP), through adult immersion and larval packet tests. The field isolates were highly resistant to DLM [Resistance factor (RF) = 3.98-38.84]. Against CYP, resistance was observed in BWN (Barwani; RF = 2.81) and MND (Mandsaur; RF = 3.23) isolates. Surprisingly, most of the isolates were susceptible to CMP (0.34-1.58). Emerging level of resistance against IVM (1.05-4.98) and FIP (0.40-2.18) was also observed in all the isolates. Significantly elevated production of esterases (p < 0.01) was 90% correlated with RF of DLM while no positive correlation between production of monooxygenase and Glutathione S-transferase with RF to DLM was noted. Multiple sequence analysis of S4-5 linker region of the sodium channel gene of all the isolates revealed a point mutation at 190th position (C190A) which is associated with DLM resistance. Treatment of resistant LDH (Ludhiana) isolate with IVM resulted in upregulation of RmABCC2 gene and insignificant upregulation of RmABCC1 and RmABCB10 genes indicating the probability of linking IVM resistance with over-expression of RmABCC2 gene. The possible tick management strategies are discussed.

Acaricide Resistance Development in Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) Populations against Amitraz and Deltamethrin on Communal Farms of the King Sabata Dalindyebo Municipality, South Africa

Chemical acaricides are widely used to control ticks and tick-borne pathogens in cattle. However, prolonged and indiscriminate use of these chemicals inevitably leads to the selection of resistant ticks. In-vitro bioassays (adult and larval immersion tests) were conducted to assess amitraz and deltamethrin resistance in Rhipicephalus (Boophilus) microplus populations from communal farms of the King Sabata Dalindyebo municipality of South Africa. Data generated on percentage inhibition of oviposition (%IO) revealed that all the tick populations assessed showed resistance (%IO ≤ 95%) to at least one of the acaricides. All six tick populations assessed for efficacy (%IO ≥ 95%) at the DD) with deltamethrin were resistant (%IO ≤ 95%) and only one of the six tick populations assessed for efficacy with amitraz was susceptible. Based on the resistance ratios (RR), the adult immersion test detected amitraz and deltamethrin resistance in three (RR ranging from 2.30 to 3.21) and five (RR ranging from 4.10 to 14.59) of the six tick populations, respectively. With the larval immersion test, deltamethrin and amitraz resistance (larval mortality < 90% at the DD) was detected in all four and three of four R. (B.) microplus populations assessed, respectively. These data are critical for the design of an effective and sustainable tick control strategy on the communal farms.

Transcriptome Profiling of Rhipicephalus annulatus Reveals Differential Gene Expression of Metabolic Detoxifying Enzymes in Response to Acaricide Treatment

Ticks are hematophagous ectoparasites of economic consequence by virtue of being carriers of infectious diseases that affect livestock and other sectors of the agricultural industry. A widely prevalent tick species, Rhipicephalus (Boophilus) annulatus, has been recognized as a prime vector of tick-borne diseases in South Indian regions. Over time, the use of chemical acaricides for tick control has promoted the evolution of resistance to these widely used compounds through metabolic detoxification. Identifying the genes related to this detoxification is extremely important, as it could help detect valid insecticide targets and develop novel strategies for effective insect control. We performed an RNA-sequencing analysis of acaricide-treated and untreated R. (B.) annulatus and mapped the detoxification genes expressed due to acaricide exposure. Our results provided high-quality RNA-sequenced data of untreated and amitraz-treated R. (B.) annulatus, and then the data were assembled into contigs and clustered into 50,591 and 71,711 uni-gene sequences, respectively. The expression levels of the detoxification genes across different developmental stages of R. (B.) annulatu identified 16,635 transcripts as upregulated and 15,539 transcripts as downregulated. The annotations of the differentially expressed genes (DEGs) revealed the significant expression of 70 detoxification genes in response to the amitraz treatment. The qRT-PCR revealed significant differences in the gene expression levels across different life stages of R. (B.) annulatus.

Evaluation of cytotoxic effects of amitraz and fipronil on digestive, reproductive and neural processes of engorged Rhipicephalus microplus (Acari: Ixodidae) female

Fipronil and amitraz are potentially toxic compounds used for controlling ticks infesting pet and livestock. The use of fipronil on large animals was limited because of its high costs while amitraz is still persisting in the market since its introduction over four decades ago. Though resistance in ticks against these pesticides has been reported worldwide since 2000, the toxicity of these chemicals at cellular level in ticks is still poorly understood. The present study aimed to examine the gross and cellular impact of fipronil and amitraz on the gut, ovaries and synganglion of engorged Rhipicephalus microplus females. Fipronil and amitraz treated tick groups showed formation of a large number of vacuoles of different size throughout the cytoplasm of generative cells whereas sessile, residual and detached digestive cells were very low in numbers. The treatment of ticks resulted in the formation of vacuolations at periphery of all oocytes. Ultra-thin sections of the synganglion revealed severe rupture of neural lamella and perineurium with apoptosis of neural cells after fipronil treatment whereas in the amitraz treated ticks, severe destruction of neuropile region and extensive vacuolation of type I and II cells of cortical region as compared to the unexposed ticks were noted.

Synergistic property of piperonyl butoxide, diethyl maleate, triphenyl phosphate and verapamil hydrochloride with deltamethrin and ivermectin against Rhipicephalus microplus ticks

The present study was taken up to evaluate the synergistic properties of piperonyl butoxide (PBO), diethyl maleate (DEM), triphenyl phosphate (TPP) and verapamil (VER) with deltamethrin (DLM) and ivermectin (IVM) against DLM and IVM resistant tick populations collected from Madhya Pradesh and Punjab states of India. The collected field tick populations were resistant to DLM (Resistance Factor [RF] in the range of 21.71-32.98) and IVM (RF in the range of 1.89-4.98). A strong synergism between DLM and, IVM with PBO and IVM with VER was noticed. The synergistic efficacy of PBO and VER with IVM in reducing the lethal concentration 50 (LC50) value (1.69-5.72 times for PBO and 3.00-10.62 times for VER) of IVM in resistant ticks suggest that a combination of these synergists with IVM can significantly enhance the effectiveness of IVM against IVM-resistant Rhipicephlaus microplus populations gradually establishing in the different parts of the country. The synergistic efficiency of PBO with DLM in reducing the LC50 value was 2.65 and 18.01 times, respectively, against DLM- resistant two R. microplus populations (KTN and LDH). The study revealed the gradual establishment of DLM and IVM resistant populations in the surveyed states suggesting the need to adopt required resistance management strategies. The use of synergists with DLM and IVM has emerged as an effective approach for controlling the acaricide-resistant ticks.

In vitro acaricidal activity of Piper longum L. against amitraz resistant Rhipicephalus microplus (Acari: Ixodidae)

The cattle tick, Rhipicephalus microplus Canestrini (Acari: Ixodidae) is one of the most important tick species severely affecting health and causes huge losses to dairy industry. Chemical acaricides are mainly applied for tick control but development of resistance, environmental pollution and contamination of milk and meat products with residues has led to exploration alternative eco-friendly tick control strategies. The dried fruits of Piper longum L. (Indian long pepper, Thippali or Pippali) generally used as flavoring agent have also been shown to have insecticidal property. Different concentrations (0.625%-10%) of alcoholic and aqueous extracts of Piper longum L. were prepared and evaluated for acaricidal activity against amitraz resistant R. microplus adult and larval stages. Against larval stages a dose-dependent mortality response was recorded for both extracts and higher acaricidal property was exhibited by the alcoholic extract with LC₅₀ and LC₉₅ (95% CL) values of 0.488% (0.48-0.49) and 1.39% (1.35-1.44), respectively. Similarly, against adult engorged females, ethanolic extract showed higher acaricidal property with LC₅₀ and LC₉₅ (95% CL) values of 4.67% (4.61-4.74) and 12.38% (12.05-12.73), respectively. Significant (p < 0.05) reduction was recorded in reproductive index of ticks treated and but no effect on hatchability of eggs was recorded in treated groups. The present study establishes acaricidal activity of P. longum fruit extracts against both larval and adult stages of amitraz resistant population of cattle tick.

Acaricides Resistance in Ticks: Selection, Diagnosis, Mechanisms, and Mitigation

Ticks are blood-feeding ecto-parasites that have a cosmopolitan distribution in tropical and subtropical regions of the world. Ticks cause economic losses in the form of reduced blood, meat and dairy products, as well as pathogen transmission. Different acaricides such as organochlorines, organophosphates, formamidines (e.g. amitraz), synthetic pyrethroids, macrocyclic lactones, fipronil, and fluazuron are currently used sequentially or simultaneously to control tick infestations. Most acaricide treatments now face increasingly high chances of failure, due to the resistance selection in different tick populations against these drugs. Acaricide resistance in ticks can be developed in different ways, including amino acid substitutions that result in morphological changes in the acaricide target, metabolic detoxification, and reduced acaricide entry through the outer layer of the tick body. The current literature brings a plethora of information regarding the use of different acaricides for tick control, resistance selection, analysis of mutations in target sites, and resistance mitigation. Alternatives such as synergistic use of different acaricides, plant-derived phytochemicals, fungi as biological control agents, and anti-tick vaccines have been recommended to avoid and mitigate acaricide resistance. The purpose of this review was to summarize and discuss different acaricides applied for tick control, their mechanisms of action and resistance selection, genetic polymorphisms in their target molecules, as well as the approaches used for diagnosis and mitigation of acaricide resistance, specifically in Rhipicephalus microplus ticks.

Establishment of antitick efficacy of a phytoformulation prepared from Annona squamosa leaf extracts for the management of acaricide resistant tick infestations on cattle

To combat the problem of acaricide resistance in ticks, efforts have been made to develop eco-friendly herbal acaricides which are safe for animal use with no possibilities of evoking environment and residual toxicity. In the present study, the acaricidal properties of a commonly available plant, Annona squamosa have been established to develop a novel antitick phytoformulation using leaf extract, suitable solvents and emulsifier for managing resistant tick infestations in animals. The quality control of the safe and stable phytoformulation using Rutin as a major constituent was maintained by HPTLC profiling. Several phytformulations (A-E) were prepared and formulation 'C' is identifried as the most effective showing 52.5-75% antitick activity against in vitro treated resistant strains of R. microplus (IVRI-IV and V) with 33.8-40.2% inhibition of oviposition while 65-85% mortality against multiacaricide resistant field populations. The phytoformulation provided 70.4% efficacy after first larval challenge in experimentally infested animals. The field efficacy of the formulation in different multilocational field trials was 68.53-77.8%. The detail antitick efficacy of the formulation along with safety and stability are explained as a component of antitck technology to manage resistant tick problem in livestock.

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.

Detection of deltamethrin, cypermethrin and flumethrin efficacy against buffalo lice-Haematopinus tuberculatus

The cattle and buffalo farm practices have been adopted differently by farmers in India but the infestation of ectoparasites including louse has been advocated in high population of animals across the country. The aim of this study was to identify the louse morphologically and determine the in vitro efficacy of the insecticides deltamethrin, cypermethrin and flumethrin against the buffalo louse, Haematopinus tuberculatus. The present research work was conducted using lice collected from organized buffalo dairy farms of Mhow block, Indore district of Madhya Pradesh, India. The adult's lice were collected from heavily infested regions of the body and tail of buffaloes. Some of the collected adult's lice were preserved for morphological identification in 70% alcohol. Briefly, in vitro treated surface bioassay utilizing a cloth rectangle that allows lice to move freely has been used. The concentrations were prepared as 30, 60, 90 and 120 ppm for deltamethrin and flumethrin, whereas for cypermethrin, 100, 200, 300 and 400 ppm concentrations were prepared in distilled water. The 600 μl of each concentration was spread evenly over a cloth rectangle held in the bottom of a Petri plate. Ten adult lice were used for each concentration in triplicate (n = 30) and the same is maintained for control. The vitality of the louse was assessed at various intervals: 30, 60, 120, 180 and 240 min. The lousicidal efficacy was determined by using in vitro bioassays with deltamethrin, cypermethrin and flumethrin. It is observed that as the concentration of insecticides increases with exposure time, mortality of lice is also increased. The current study reveals that cypermethrin and flumethrin were effective in their recommended doses but in the case of deltamethrin, the lice showed a low level of resistance. Furthermore, this type of study on buffalo louse has not conducted in Mhow region of Madhya Pradesh where heavy infestation of lice occurs on buffalo.

Development of acaricide resistance in tick populations of cattle: A systematic review and meta-analysis

The development of acaricide resistance in ticks infesting cattle is a major problem in the livestock industry in tropical and subtropical regions worldwide. To determine the current global trends and prevalence of acaricide resistance development (ARD) in tick populations of cattle, a systematic review and meta-analysis with an emphasis on Rhipicephalus (Boophilus) microplus was conducted. Data searches from five English electronic databases yielded 88 journal articles published between 1992 and 2020. In total, 218 in - vitro bioassays were used to investigate 3939 tick populations of cattle; of these, the 57.6% that exhibited ARD were largely limited to South America (Brazil), Central America (Mexico), and Asia (India). A total of 3391 of these tick populations were R. (B.) microplus, of which 2013 exhibited ARD. Random effects meta-analyses indicated that the exhibition of ARD was higher in R. (B.) microplus (66.2%) than in other tick species. Global prevalence estimates of ARD in R. (B.) microplus vary as a function of geography, detection methods, and acaricide compounds. In general, high heterogeneity was noted among the studies. However, homogeneity was observed among studies from India, suggesting the establishment of acaricide resistance in Indian R. (B.) microplus populations. Current tick control interventions are urgently required to limit the evolution and implications of resistance development.

Evaluation of acaricidal resistance status of Rhipicephalus microplus ticks from the hilly state (Uttarakhand) of India and evaluation of efficacy of a natural formulation for the management of resistant ticks

The resistance status against deltamethrin, cypermethrin, coumaphos and ivermectin was assessed of Rhipicephalus microplus from five districts of Uttarakhand, through adult immersion test and larval packet test. The field isolates were highly resistant to deltamethrin (median resistance ratio [RR₅₀] = 9.10-29.13-fold) followed by cypermethrin (2.23-3.55). Surprisingly the isolates were susceptible to coumaphos (0.34-3.17). Emerging resistance against ivermectin (1.55-3.27) was also observed in all the isolates. Elevated levels of esterases (enzyme ratio = 2.93-5.84-fold), glutathione S-transferases (5.10-10.06) and monooxygenases (1.68-4.02) in resistant fields isolates were highly correlated (47.4-86.0%) with the resistant factor (RR₅₀) determined by bioassay. All the isolates except Uttarkashi possess mutation at the 190th position in domain II of the sodium channel gene. As a mitigation strategy an Ageratum conyzoides-based characterized natural formulation was tested against all the isolates and was found effective at the concentration of 10.1-11.5%. The possibility of using the natural formulation for the management of multi-acaricide resistant ticks is discussed.

Characterization of deltamethrin, cypermethrin, coumaphos and ivermectin resistance in populations of Rhipicephalus microplus in India and efficacy of an antitick natural formulation prepared from Ageratum conyzoides

Rhipicephalus microplus is posing a serious threat to productive animal husbandry. Excessive use of synthetic chemicals in tick management has led to the development of resistant tick populations. Characterization of resistance to deltamethrin, cypermethrin, coumaphos and ivermectin in ticks is necessary to develop a suitable and sustainable control strategy. Based on adult immersion test and larval packet test, the resistance ratios (RR₅₀) for adults and larvae of R. microplus populations from two Indian states ranged from 3.8 to 19.4 and 1.35-25.0 against deltamethrin, 0.061-26.3 and 0.22-19.2 against cypermethrin, and 0.2-9.5 and 0.01-3.1 against coumaphos, respectively, were recorded. Moreover, the RR₅₀ for adults ranged from 0.212 to 3.87 against ivermectin. The RR₅₀ for different acaricides was significantly (p<0.01) correlated with esterases, Glutathione S-transferase and monooxygenase activity. A point mutation at the 190th position of the domain II S4-5 linker region of the sodium channel gene in synthetic pyrethroids (SP) resistant populations was also detected. An antitick natural formulation prepared from the plant Azeratum conyzoides and containing two major compounds, Precocene-I (7‑methoxy-2, 2-dimethyl 2H-chromene) and Precocene II (6, 7-dimethoxy-2, 2-dimethyl- 3-chromene), was developed and tested against the resistant ticks. The LC₅₀ values of the natural formulation against the resistant populations were in the range of 4.31-5.33% irrespective of their RR₅₀ values. Multi-acaricide resistant populations of R. microplus are established in India and the A. conyzoides based natural formulation can be used for its management.

Comparative susceptibility of Rhipicephalus microplus collected from the northern state of India to coumaphos, malathion, deltamethrin, ivermectin, and fipronil

The chemical-based tick management method is gradually losing its clutch due to the establishment of resistant ticks. For development of region-specific tick management strategies, the present study was aimed to evaluate the comparative resistance profile of Rhipicephalus microplus isolates collected from seven districts of Uttar Pradesh, a northern state of India. Comparative analysis of the dose-response data using adult immersion test (AIT) against coumaphos, malathion, deltamethrin, ivermectin, and fipronil revealed that all the isolates were resistant to discriminating concentration of deltamethrin having LC₅₀ of 295.12-436.52 ppm with a resistance ratio of 22.02-32.58. An emerging low level of ivermectin resistance (resistance ratio, RR₅₀ = 1.03-2.26) with LC₅₀ in the range of 22.39-48.98 ppm was found across the isolates. The coumaphos was highly effective against all except Amethi (AMT) isolate. Similarly, malathion was efficacious against most of the isolates except Pratapgarh (PRT) and Sultanpur (SUL) isolates showing LC₅₀ of 5128.61 and 5623.41 ppm, respectively. All the isolates were responsive to fipronil. Comparative detoxifying enzymes profiles revealed a significant correlation between the increased activity of esterase and deltamethrin resistance. The GST activity was 51.2% correlated with RR₅₀ of malathion while esterase activity was significantly correlated (68.9%) with RR₅₀ of coumaphos. No correlation between the ivermectin resistance and enzyme activity was established. Multiple sequence analysis of S4-5 linker region of the sodium channel gene of all the isolates revealed a point mutation at 190th position (C190A) which is associated with deltamethrin resistance. The possible tick management strategies in this part of the country are discussed.

Acaricidal activity of the hexanic and hydroethanolic extracts of three medicinal plants against southern cattle tick Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

The southern cattle tick Rhipicephalus microplus is a major problem for the cattle industry in tropical and subtropical areas worldwide. Chemical products are commonly applied to control it; however, their indiscriminate use has resulted in the appearance of resistant lineages. In the last decades, plants have been used as an alternative to conventional acaricidal drugs, as several plant compounds repel activity, decrease the reproductive potential and reduce the survival rate of ticks. For this reason, the in vitro efficacy of hexanic and hydroalcoholic extracts of Randia aculeata, Moringa oleifera and Carica papaya were evaluated against the larvae and engorged females of R. microplus. Larval packet tests and adult immersion tests were performed with seven concentrations of each of the extracts. The extracts obtained with hydroethanolic solution (polar solvent) exhibited a higher acaricidal activity than extracts prepared with n-hexane (non-polar solvent). Hydroethanolic extracts of R. aculeata seed and shell showed the highest larvicidal activity against R. microplus (100 and 91% mortality, respectively) at a concentration of 100 mg/mL. Randia aculeata (seed and shell), M. oleifera and C. papaya treatments at the same concentration (100 mg/mL) also resulted in adult mortality of 85, 75, 66 and 55%, respectively. The adult immersion test showed that hydroethanolic extracts derived from R. aculeata seed significantly reduced the index of egg laying and increased the percentage inhibition of oviposition of female ticks at a concentration of 100 mg/mL. These results indicate that the tested extracts exhibit acaricidal activity and could be considered as potential agents for the development of alternative natural acaricides against R. microplus.

Genotyping of Deltamethrin Resistance in Rhipicephalus (Boophilus) microplus Population in Kerala, South India

PURPOSE

Genotyping of Rhipicephalus (Boophilus) microplus for polymorphisms in deltamethrin-resistant loci of sodium channel gene by allele-specific PCR (AS-PCR).

METHODS

Adult R. (B.) microplus ticks were collected from naturally infested cattle in Kerala. The larval packet test (LPT) was performed with deltamethrin and dose response data were analysed by probit method. Adult and larval tick DNA were amplified by PCR and later sequenced to identify mutations, if any, in the domain II S4-5 linker and domain III S6 regions in para voltage-gated sodium channel gene, at loci that were previously documented to be associated with deltamethrin resistance. Allele-specific PCR was performed for the amplification of target gene locus (C190A and T2134C) to genotype 1000 larvae each, at these loci. Genotype frequency was statistically analysed by Chi-square test.

RESULTS

Bioassay using LPT revealed that LC₅₀ and LC₉₅ values of all the R. (B.) microplus isolates in this study were more than double the reported values of reference susceptible strain. Sequence analysis of the PCR amplicons of domain II S4-5 linker of voltage-gated sodium channel gene revealed C190A mutation, A271G mutation as well as A-G mutation at 217th position. AS-PCR done to genotype C190A mutations revealed a frequency of 6%, 15% and 64%, respectively for homozygous-susceptible (SS), heterozygous (RS) and homozygous-resistant (RR) genotypes. In domain III S6 region of the gene, C2121T and A2102T mutations were observed. AS-PCR to genotype the previously reported T2134C mutation revealed 100% SS genotype in R. (B.) microplus isolates of Kerala.

CONCLUSIONS

Genotyping of R. (B.) microplus isolates of Kerala for target site mutations reportedly associated with deltamethrin resistance revealed a significantly high frequency of resistant genotypes at II S4-5 linker of voltage-gated sodium channel gene. This study forms the first report of such mutations in Kerala, south India and demands serious attention in the light of increased prevalence of tick-borne haemoparasitic infection.

Ivermectin resistance in the multi-host tick Hyalomma anatolicum (Acari: Ixodidae) in India

The multi-host tick, Hyalomma anatolicum is a widely distributed vector of many pathogens of veterinary and public health importance. Ivermectin (IVM), as an alternative to control pyrethroid-resistant ticks, has been used extensively for the past 4-6 years in tropical and sub-tropical countries including India resulting in declining tick control efficacy. The present study used adult immersion test (AIT) to examine the resistance status of H. anatolicum collected from three districts in the Indian state of Gujarat against ivermectin. Probit analysis was used for calculation of concentration-mortality regressions; concentrations required for 50% mortality (LC₅₀) and 95% mortality (LC₉₅), along with confidence intervals; slope of mortality; % inhibition of oviposition; and discriminating concentration (DC). The calculated LC₅₀ and LC₉₅ estimates were utilized to determine resistance ratios (RR₅₀, RR₉₅) and the resistance levels (RL) of the field ticks compared to the susceptible population. The DC (2 x LC₉₅) for IVM was calculated as 84.48 ppm, using susceptible H. anatolicum ticks (KHD). Lower estimates of the coefficient of non-determination (1-R²) for AIT ranged from 0.06 to 0.27, and the range of RR₅₀ and RR₉₅ values against IVM was estimated to be from 1.43 to 52.06 and 1.14 to 71.99, respectively, which indicated a varying degree of resistance among the field tick populations. Based on RR₅₀ values, tick populations from Danta and Palanpur showed resistance level IV and II, respectively. Another four populations (Vadgam, Kankrej, Saraswati and Sidhpur) were classified as having level I resistance status against IVM. To our knowledge, this is the first report of ivermectin resistance in H. anatolicum from Gujarat, India.

Assessment of acaricidal activity of nanoscale ZnO encapsulated piperine formulation against Rhipicephalus microplus

This study aims to synthesise and evaluate the acaricidal activity of nanoscale zinc oxide piperine formulation (NZPF) against Rhipicephalus microplus ticks. NZPF was prepared by using zinc oxide nanoparticles (ZnONPs) and piperine by employing encapsulation technique; characterised by UV spectroscopy, Fourier transformed infrared analysis, X-ray diffraction, dynamic light scattering, zetapotential and scanning electron microscopy. Acaricidal activity of the NZPF on R. microplus was evaluated using larval packet test (LPT) and adult immersion test (AIT). LPT against R. microplus larvae showed an LC₅₀ at 1 mg/l for NZPF followed by 2 and 3 mg/l for ZnONPs and piperine, respectively. AIT against R. microplus showed an LC₅₀ at concentration of 3 mg/l for NZPF followed by 6 mg/l for ZnONPs and 7 mg/l for piperine. In both LPT and AIT, LC₅₀ values of ZnONPs and NZPF were significantly lower compared to deltamethrin. NZPF showed significant ovulation inhibitory activity with lower IC₅₀ and IC₉₉ values compared to ZnONPs and piperine. NZPF has been proved to be the better alternative to routine chemical acaricides for control of tick infestation of cattle in the wake of acaricidal resistance, but safety issues need to be addressed before clinical application.

A retrospective review on ixodid tick resistance against synthetic acaricides: implications and perspectives for future resistance prevention and mitigation

The ending of the nineteenth-century was characterized by an escalation of ticks and tick-borne diseases that resulted in the death of many cattle. This necessitated the search for an effective means of tick control. Arsenicals were introduced in Australia in 1895, and arsenic-based dipping vats went on to be used for about 40 years until resistance was found in ticks and more effective alternatives - chemical acaricides - were developed after World War II. However, the development of resistance by ticks, environmental persistence, and mammalian toxicity militated against the sustained use of subsequent chemical acaricides. Furthermore, the development of resistance is a phenomenon that would always evolve, and the multiple mechanisms underlying the synthetic acaricides resistance are of great importance for future integrated control of ticks and tick-borne diseases. Hence, this study retrospectively reviewed the development of synthetic acaricides and the underlying mechanisms of tick resistance against synthetic acaricides in the hope of providing the implications and perspectives for resistance prevention and mitigation for future tick control.

Development of an efficient antitick natural formulation for the control of acaricide-resistant ticks on livestock

Animal production has a key role in global economic development and food security. Ticks, specifically Rhipicephalus microplus cause substantial economic and health impacts on more than eighty percent of the world cattle population. Though synthetic acaricides play a major role in tick management, their injudicious usage has caused environmental pollution and also promote the establishment of multi-acaricide resistant tick populations which is a matter of great concern. To provide an effective tool for controlling these resistant ticks, the present work was aimed to develop safe and inexpensive antitick natural formulations. Our bioprospection studies of Ageratum conyzoides plant established it as a species potentially having strong acaricidal activity due to the presence of potent acaricidal phyto-chemicals. To develop a suitable antitick natural formulation, 41 samples/fractions/formulations were prepared from the dry powder of the whole aerial part of the A. conyzoides plant using different techniques and delivery matrices. The strongest antitick effect was recorded for formulation ACF6, which demonstrated 87 ± 6% mean mortality with 57 % inhibition of oviposition in treated female ticks. Ticks treated with the ACF6 formulation showed a significant (p < 0.001) reduction in cuticular protein (1.238 ± 0.01 mg/mL) as compared to control ticks (2.928 ± 0.01 mg/mL) but no significant difference in chitin content of treated ticks and control ticks was observed. The formulation was found safe in a rat model as no significant differences in biochemical and haematological parameters among treated and control rats were noted. Histopathological studies indicated no sign of hepatocellular necrosis and no significant changes in the weights of liver and spleen was recorded. The overall in vivo efficacy of the formulation was 85 % for experimentally infested cattle with direct mortality of more than 80 % within 96 h post-application. The lethal effect of the formulation was in the form of drying and dead ticks 1-2 d after application. The developed formulation has the potential to be adopted as an alternative tick control measure in an ecofriendly manner.

Vaccine approaches applied to controlling dog ticks

Ticks are considered the most important vectors in veterinary medicine with a profound impact on animal health worldwide, as well as being key vectors of diseases affecting household pets. The leading strategy applied to dog tick control is the continued use of acaricides. However, this approach is not sustainable due to surging tick resistance, growing public concern over pesticide residues in food and in the environment, and the rising costs associated with their development. In contrast, tick vaccines are a cost-effective and environmentally friendly alternative against tick-borne diseases by controlling vector infestations and reducing pathogen transmission. These premises have encouraged researchers to develop an effective vaccine against ticks, with several proteins having been characterized and used in native, synthetic, and recombinant forms as antigens in immunizations. The growing interaction between domestic pets and people underscores the importance of developing new tick control measures that require effective screening platforms applied to vaccine development. However, as reviewed in this paper, very little progress has been made in controlling ectoparasite infestations in pets using the vaccine approach. The control of tick infestations and pathogen transmission could be obtained through immunization programs aimed at reducing the tick population and interfering in the pathogenic transmission that affects human and animal health on a global scale.

Control of Rhipicephalus annulatus resistant to deltamethrin by spraying infested cattle with synergistic eucalyptus essential oil-thymol-deltamethrin combination

The current study investigated the synergistic effect of combinations containing deltamethrin (D), Eucalyptus essential oil (E), and the thyme essential oil component thymol (T), against a field population of Rhipicephalus annulatus in Egypt that was characterized to be resistant to D. Solutions of T, E, or TE at concentrations of 1.25-5% were combined with 5% deltamethrin at different dilutions (0.25-2 mL/L). Results of the adult immersion test used to estimate the in vitro acaricidal activity of these combinations at 5% yielded LC₅₀ values for D, E-D, T-D, and TE-D of 3.87 mL/L, 3.89 mL/L, 0.14 mL/L, and 0.05 mL/L, respectively. Biochemical analyses using whole-body homogenate of ticks from the in vitro tests revealed that the lowest acetylcholinesterase and glutathione peroxidase activity, and the maximum lipid peroxidation were recorded in ticks treated with 5% TE-D. Glutathione content significantly decreased (p ≤ 0.05) in all treated ticks. Three groups, each containing five cross breed cattle naturally infested with R. annulatus from the same area where resistance to D was detected, were sprayed twice at two-week intervals using 1 mL/L of 5% solutions of D, T-D, or TE-D. Overall efficacy of the D, T-D, and TE-D sprays by day 30 post-treatment was 21.6, 88.3, and 95 %, respectively. Ticks collected from infested cattle three days after treatment with the D spray deposited egg masses that were able to hatch, deposited small masses of eggs unable to hatch when exposed to the T-D spray, and laid few eggs that didn't hatch when sprayed with the TE-D combination. Values for liver and kidney function parameters were comparable in cattle before and after treatment with the combination sprays tested. The TE-D spray overcame the insensitivity to D of this R. annulatus population in Egypt, which also highlighted the significant synergistic effect of thymol on the acaricidal activity of deltamethrin observed in vitro. Acaricidal activity of the TE-D combination apparently has deleterious effects on multiple tick systems involving inhibition of acetylcholinesterase, increased lipid peroxidation, and oxidative stress. These findings document that combinations of natural and synthetic products can be part of integrated management solutions to the problem with widespread resistance to pyrethroids like deltamethrin in populations of cattle ticks, including R. annulatus, around the world.

Acaricidal Activity of Artemisia nilagirica Leaves Against Rhipicephalus (Boophilus) annulatus Ticks

Since time immemorial, human beings have used various parts of plants in either prevention or treatment of ailments. Plants are rich sources of secondary metabolites such as alkaloids, steroids, terpenoids, flavonoids, and phenolic compounds with a high structural diversity. Many plants/herbs with specific biological activities such as antitumor, antioxidant, anti-inflammatory, antifungal, sedative, and acaricidal activity have been reported. Artemisia nilagirica (C. B. Clarke) Pamp. (Compositae) is a plant traditionally used for insect control in the southern part of India. Previous studies have demonstrated the activity of Artemisia species against pests. The present study thus evaluates the acaricidal activity of crude ethanolic extract of A. nilagirica leaves and its fractions against Rhipicephalus (Boophilus) annulatus. Ticks are ectoparasites that transmit several protozoal, viral, and rickettsial diseases. In south India, R. (B.) annulatus is the commonly observed tick species. Control of these acarine parasites that adversely affect milk and meat production is a tough task. Chemical acaricides such as organophosphates, synthetic pyrethroids, amitraz, and ivermectin are commonly used in tick control. The high cost, environmental hazards, and development of acaricidal resistance are some of the drawbacks of these chemical acaricides. Plant-based formulations are one of the promising approaches for the control of ectoparasites. Previously, extracts from various medicinal/aromatic plants were reported for acaricidal activity from our laboratory, such as Tetrastigma leucostaphylum (Dennst.) Alston, Chassalia curviflora (Wall.) Thwaites, Jatropha curcas L., and Ageratum conyzoides Hieron. Biochemical quantification, fluorescence analysis, and primary phytochemical analysis are already reported for the ethanolic extract and its fractions of areal parts of A. nilagirica. Phytochemical characterization of ethanolic extract of A. nilagirica from Kerala, India was shown to have the presence of terpenoids, flavonoids, steroids, saponins, fixed oils and fats, tannins, and glycosides.

Genotyping amitraz resistance profiles in Rhipicephalus microplus Canestrini (Acari: Ixodidae) ticks from Punjab, India

Acaricide resistance is one of the greatest threats to sustainable and effective control of vector ticks worldwide. The amitraz resistance status in cattle tick, Rhipicephalus microplus populations collected from 18 districts of Punjab in north-western India were characterized using bioassay and molecular assays. The modified larval packet test was used and the resistance factors (RF) against amitraz for the field populations were in the range of 0.36-4.85, indicating level I resistance status in ten populations. Characterization of a partial segment of the octopamine/tyramine (OCT/Tyr) receptor gene of R. microplus field populations from Punjab revealed a total of 18 nucleotide substitutions in the coding region out of which 5 were non-synonymous substitutions. Three of these non-synonymous substitutions (T8P, V15I and A20 T) were earlier reported in American and South African populations of R. microplus. Among the two single nucleotide polymorphisms (A22C-T8P; T65C-L22S) potentially linked to amitraz resistance in American, South African and Zimbabwean resistant populations, only the T8P substitution was recorded from the Barnala population. The PCR-RFLP assay using EciI restriction enzyme was used for genotyping of the larvae as homozygous resistant (RR), homozygous susceptible (SS) and heterozygous (SR). Genotyping of 514 larval DNA samples from 18 field populations revealed 92.8 % larval population as SR and the remaining 7.2 % as RR genotypes. The percentage of resistant alleles in the tick populations was 53.6 (range 50.0-57.2) indicating its moderate distribution in the region. The present study is the pioneer report establishing the hypothesis that amitraz-resistance is recessively inherited and heterozygous individuals show phenotypic susceptibility to the drug in the Indian tick populations.

The potential of Allium sativum and Cannabis sativa extracts for anti-tick activities against Rhipicephalus (Boophilus) microplus

The efficacy of Allium sativum and Cannabis sativa against Rhipicephalus microplus ticks was evaluated using the adult immersion and the larval packet test. In addition, an in silico approach was utilized by performing a docking study in order to identify the active ingredients from both plants. Results showed a comparatively high lethal effect of A. sativum and C. sativa on egg laying (index of egg laying = 0.26 and 0.24, respectively), egg hatching (33.5 and 37.1, respectively), and total larval mortality (100%, both), at 40 mg/mL. When applied to cattle which had been inoculated with larvae ticks, it was observed that a 45% solution of both herbal extracts significantly reduced the number of ticks by 96 h post treatment. We analyzed in silico 27 known active molecules from both plants and identified in the PubChem database to explore the hypothesis that the effect found on ticks was based on inhibition of acetylcholinesterase (AChE). Vitamin E and cannabidiol are the most potent AChE inhibitors with docking scores of -15.85 and -14.38, respectively. Based on these findings, we conclude that A. sativum and C. sativa may potentially be used for the control of R. microplus, and should be further investigated as a potential supplement to or replacement of synthetic acaricides.

Detection of single nucleotide polymorphism in the para-sodium channel gene of Rhipicephalus annulatus populations from Egypt resistant to deltamethrin

Rhipicephalus annulatus field populations collected from small cattle farms in Beni-Suef province in Egypt were evaluated for deltamethrin resistance by toxicological in vitro bioassays (adult immersion test-AIT and larval packet test-LPT). Moreover, a quantitative PCR high resolution melting (PCR-HRM) technique was used to detect nucleotide substitutions in the voltage-gated sodium channel (Na-channel) gene. By the in vitro bioassays, the examined ticks were phenotypically categorized as deltamethrin susceptible (populations El-Wasta - A, and El-Hakamna - C) or resistant (populations El-Wasta - B, El-Hakamna - D, EL-Halabia - E, and Kom-abokhalad - F). Based on LPT findings, the phenotypic resistant populations were found to have a resistance ratio between 6.5 - 10.8. The PCR-HRM genotyping of the ticks showed variable melting curves among the populations in domain II of the Na-channel gene. Analysis of the curves showed the presence of wild type, mutant homozygous, and mutant heterozygous tick individuals. By sequencing the PCR amplified fragments, the C190A mutation was the only detected nucleotide polymorphism of domain II among the phenotypically resistant populations, which was present in 39.5 % (34/86) of the ticks tested. On the other hand, the phenotypically susceptible populations A and C did not show C190A mutant homozygous (RR) individuals. Meanwhile, in domain III all of the examined populations revealed melting curves like the wild type. Furthermore, the sequence analysis of these populations confirmed the absence of SNPs in domain III. The C190A single point mutation was detected for the first time in domain II of the Na-channel gene of deltamethrin-resistant R. annulatus in Egypt using PCR-HRM. Screening for efficacy of chemical compounds used by farmers to control ticks on cattle should be considered as part of animal health programs to manage the emerging resistance to acaricides in R. annulatus populations.

Toxicity, repellency and anti-cholinesterase activities of thymol-eucalyptus combinations against phenotypically resistant Rhipicephalus annulatus ticks

The current study was designed to compare the acaricidal activity of pure thymol (T) crystals, eucalyptus oil (E), and their combinations (T + E) at concentrations ranging from 0.625 to 10% against phenotypically deltamethrin-resistant Rhipicephalus annulatus ticks. The adulticidal, larvicidal, ovicidal, and repellent activities of the tested compounds and their possible mechanism of action were studied. Thymol showed 93.3% adulticidal activity at 10% concentration, whereas at 2.5% it achieved 100% larvicidal activity. Eucalyptus oil had a significant effect on tick adults at concentrations > 5%, and at 10% concentration it showed 96.7% adulticidal activity and stopped the egg hatching. On deltamethrin-resistant larvae, the median lethal concentration (LD₅₀) was 0.61, 7.5, and 0.61% for T, E, and T + E combinations, respectively, and repellent activities were 85.7, 62.5, and 100% at the 10% concentration used. Combinations of T + E did not induce additional effects as adulticidal and larvicidal in a comparison with T treatments. The tick's acetylcholinesterase significantly decreased as a result of all treatments including deltamethrin, whereas lipid peroxidation significantly increased compared with the control untreated ticks. The glutathione content significantly decreased as a result of all treatments except for treatments with 10% thymol and its combination with eucalyptus oil. Moreover, 10% eucalyptus oil significantly decreased the tick's glutathione peroxidase and catalase activities reflecting the attenuation of antioxidant defense in the ticks. In conclusion, thymol and eucalyptus oil showed excellent activities against deltamethrin-resistant R. annulatus isolates. Their action may be mediated via acetylcholinesterase inhibition. The effect of thymol-eucalyptus combinations recorded higher activities as an ovicidal and as a repellent.

Emergence of fipronil resistant Rhipicephalus microplus populations in Indian states

The intensive usage of chemical acaricides for the control of the cattle tick Rhipicephalus microplus has resulted in the development and establishment of multi-acaricide resistant populations. Fipronil, a phenylpyrazole insecticide, is currently marketed in India for the management of this important veterinary tick species. Here, we tested Indian isolates of R. microplus which have developed multi-acaricide resistance, for their susceptibility to fipronil. Twenty-five field isolates from five agro-climatic zones of the country were collected and tested by adult immersion test (AIT) and larval packet test (LPT). Sixteen isolates with resistance factor (RF) in the range of 1.56-10.9 were detected using LPT, whereas only 11 isolates with RF ranging from 1.05 to 4.1 were detected using AIT. A significant variation of RF between both tests was found, which raises doubt about the suitability of larva-based assays in screening of fipronil resistance. The data indicated possible cross-resistance between groups of acaricides in fipronil-resistant tick populations.

Standardization of tick specific biochemical tools for estimation of esterases, monooxygenases and glutathione S-transferase for characterization of acaricide resistance

Protocols to determine metabolic resistance in ticks were mainly derived from reports published using mosquitoes and agriculturally important insects without prior standardization. In the present study, biochemical assays were standardized to quantify acaricide metabolizing enzymes in tick homogenates. Three variables viz., age, number of larvae and reaction time were optimized using reference susceptible IVRI-I and deltamethrin resistant IVRI-IV (Resistance Factor = 194) tick strains. The optimum conditions for estimation of general esterases were 10-15 day old 40 larvae with 15 mins reaction time, 15-20 day old 40 larvae with 20 mins reaction time for Glutathione S- transferase, while 10-15 day old 80 larvae with 5 mins reaction time for monooxygenase. The standardized protocols were further validated in multi acaricide resistant strain (IVRI-V) and in nine field isolates having variable resistant factors to different acaricides. In all the nine heterogeneous field isolates, a significant correlation (p < .05) between resistance to synthetic pyrethroids and over-expression of esterases and monooxygenase was noticed. Similarly, esterases and GST activities were significantly correlated with resistance to organophosphates. The details of the assay protocol are explained for adoption in different laboratories.

Characterization of acaricide resistance in Rhipicephalus microplus populations infesting cattle in northeastern India and assessment of local plant extracts for tick management

In the present study, the tick isolates were collected from Assam state, of northeastern region (NER) and characterized using in vitro bioassay, biochemical and molecular assays. Comparing LC₅₀ value of susceptible IVRI-I and larvae of field isolates, revealed that RF against deltamethrin was highest for Morigaon (MGN = 21.8) and lowest for Sonitpur (SNP = 3.3) isolate. The RF against cypermethrin was highest for Nagaon (NGO = 5.0) and lowest for Barpeta (BPT = 1.2) isolate. Against coumaphos, the highest RF of 4.5 was calculated for BPT (4.5) and lowest for NGO (1.3) isolate. While using adults based assay, highest RF of 24.68 against deltamethrin and lowest RF of 4.96 was determined for MGN and SNP isolate, respectively. In contrast to the results obtained using larvae, against cypermethrin, highest RF was recorded for Kamrup Metropolitan (KMP) while it was NGO isolate using larvae. In case of coumaphos, both larvae and adults of BPT isolate were also highly resistant and lowest RF was detected in SNP (2.30) isolate. All the isolates were susceptible to ivermectin. A significant correlation (p < 0.01) between deltamethrin resistance and higher expression of glutathioneS-transferase was observed while no correlation with esterase and monooxygenase enzymes activity was noted. For the development of possible ecofriendly control measure, different accessions of Argemone mexicana and Datura metel plant species were collected, extracted and screened against adult ticks. Two accessions, NEA-03 and NED-06 collected from Amlighat and Diphu (East Karbi Anglong) were more than 90 % effective. Further dose response study of these accessions determined the LC₅₀ values of 4.86 and 3.96 %, respectively.The resistance status of the collected tick isolates was compared with the data generated from other regions having higher livestock population and possibility of exploitation of identified plant species for the development of natural antitick product is discussed.

Menace of acaricide resistance in cattle tick, Rhipicephalus microplus in India: Status and possible mitigation strategies

Livestock in general and dairy sector in particular plays a vital role in the Indian economy and in the socio-economic development of millions of people. Rhipicephalus microplus, a one-host and the most prevalent cattle tick in various agro climatic zones of India. This tick species is responsible for severe economic losses to livestock owners both through the direct effects of blood sucking, injection of toxins and indirectly by transmitting pathogens. Due to inadvertent and indiscriminate use of chemicals to kill ticks, field tick population has developed resistance to almost all chemicals that are used to manage them. The intention of this review is to provide the current status of resistance in ticks, the possible mechanisms of resistance operating in the tick population, factors contributing to the development of resistance and the managemental strategies.

Acaricide resistance in Rhipicephalus microplus collected from selected districts of Madhya Pradesh, Uttar Pradesh and Punjab states of India

The isolates of Rhipicephalus microplus collected from Madhya Pradesh (MP), Punjab (PJB) and Uttar Pradesh (UP) states of India were characterized using laboratory standardized adult immersion test (AIT) against macrocyclic lactone (ivermectin), synthetic pyrethroids (cypermethrin and deltamethrin), organophosphates (coumaphos and diazinon) and phenylpyrazole compounds (fipronil). Out of the six isolates tested, five isolates except MTH were resistant to deltamethrin and cypermethrin at level II with RF ranging from 16.4 to 24.02 and 7.05 to 13.2, respectively. In case of organophosphates, coumaphos was less effective showing resistance level II (RF 8.52-11.2) in all the six populations compared with diazinon to which three isolates (MHW, RWA and AGS) were resistant at level II. Except MTH, other five isolates were categorized at level I with RF ranging from 1.53 to 3.02 against ivermectin. The phenylpyrazole compound however was found effective, and none of the isolates could survive at a discriminating concentration. The possible strategy for the management of multi-acaricide-resistant ticks in the surveyed districts was discussed in the present study.

Comparative impact of coumaphos, amitraz and plant extract of Ageratum conyzoides on the oogenesis of Rhipicephalus microplus

The present experiment was conducted to evaluate and compare the impact of Ageratum conyzoides plant extract (ACE) with routinely used synthetic acaricides i.e., amitraz and coumaphos on the oogenesis of engorged adult females of Rhipicephalus microplus tick. On the day of dropping from the host, panoistic ovary of R. microplus appeared white in colour, horseshoe shaped, hollow tubular organ with immature oocytes predominantly in dorsal groove. Different developmental stages of oocytes (I-V) proceed simultaneously and asynchronously. Oocytes showed gradual increase in size, deep brown colored with accumulation of eggs in oviduct during 24-72 hours of development.At LC₉₀ concentration a highly significant (p < 0.001) cessation of egg laying after exposure to amitraz and ACE while significant reduction (p < 0.01) of egg laying in coumaphos treated ticks was observed. Upon dissection of treated ticks, uterus and oviduct packed with eggs, which failed to pass out was observed. The histo-architectural alterations including presence of extensive vacuolation, alteration of oocyte morphology, deformation of chorion and disorganization of yolk granules were observed in the treated ovaries. Histochemically, low level of storage or synthesis of essential elements viz., proteins, polysaccharides and lipids in treated oocytes responsible for reduction of fertility and inhibition of progress of vitellogenesis was observed.

The effect of sublethal concentrations of deltamethrin and alphacypermethrin on the fecundity and development of Ixodes ricinus (Acari: Ixodidae) eggs and larvae

Two pyrethroids, deltamethrin (D) and alphacypermethrin (AC), have been used as commercial products for tick control worldwide. However, the effects of sublethal doses of these compounds on various tick species and their developmental stages have not been fully explored yet, although such knowledge could contribute to a more effective application of both pyrethroids and simultaneous reduction of their costs and undesirable side effects, including the harmful impact on other organisms and environmental contamination. This study investigates the effect of sublethal concentrations of D and AC applied to engorged females on the fecundity, development of eggs and larvae, and the number of offspring in the Ixodes ricinus (L.) tick, which is the most important vector of tick-borne diseases of humans in Europe. After detachment from rabbit's skin, fully engorged I. ricinus females were treated with 20 μl of pyrethroid solutions at five concentrations from 0.01562 to 0.25% and kept at 28 °C and 75% relative humidity. The impact of the pyrethroids on maturation and development of eggs as well as development of larvae was assessed based on parameters of the preoviposition and oviposition periods and the course of embryogenesis and egg hatch. The investigations have shown that both tested acaricides reduce the reproductive rate in I. ricinus females by inhibition of egg development and disturb embryonic development and larval hatch. Females did not lay eggs at concentrations higher than 0.0625% AC and 0.125% D. The lower concentrations of both pyrethroids disturbed or inhibited the embryogenesis and egg hatch in I. ricinus.

In vitro assessment of synergistic combinations of essential oils against Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

Rhipicephalus (Boophilus) microplus (Acari: Ixodidae), is one of the most important ectoparasite of cattle, responsible for causing severe economic losses in the tropical and subtropical regions of the world. The development of resistance to most of the commonly used chemical acaricides has stimulated the search for new herbal products as an eco-friendly tick control alternative. The aim of the present study was to evaluate the in vitro acaricidal activity of essential oils (EOs) of cloves (Syzygium aromaticum), bark of cinnamon (Cinnamomum zeylanicum) and leaves of lemon grass (Cymbopogon citratus) against unfed larvae of R. (B.)microplus by larval packet test. Also, various combinations were prepared by mixing of equal concentrations of any two and all three EOs and used to study the effects of interactions of mixtures against larvae of R. (B.) microplus. The lethal concentrations at 50% (LC₅₀), 90% (LC₉₀) and 99% (LC₉₉) with 95% confidence limits (CL) were estimated by Probit analysis using PoloPlus. The computer software, CompuSyn, was used for determining the effects of interactions (synergistic, additive or antagonistic) of EO mixtures by calculation of Combination index (CI) and Dose-reduction index (DRI). Among the individual and mixture of two EOs, cinnamon EO and cinnamon EO + lemon grass EO combination showed highest acaricidal activity against R. (B.) microplus larvae. Further, the combination of cinnamon EO + lemon grass EO showed high synergism with CI value of 0.381, followed by cinnamon EO + clove EO showing moderate synergism whereas, clove EO + lemon grass EO showed only additive effect, with favorable dose reduction for each constituent drug in all three combinations. The combination of all three EOs (1:1:1) showed high synergism (CI value of 0.376) and favorable dose reduction (DRI index of 8.19, 25.64 and 4.64 for clove, cinnamon and lemon grass EOs, respectively) against R. (B.) microplus larvae.

Acaricidal efficacy of deltamethrin-zinc oxide nanocomposite on Rhipicephalus (Boophilus) annulatus tick

In the veterinary field, there is a great concern about the issue of acaricides resistance in cattle ticks. A comparative study was designed to evaluate the in vitro acaricidal efficacy of imidacloprid nano-emulsion, zinc oxide nanoparticles (ZnO NPs), silver nanoparticles (Ag NPs), deltamethrin, deltamethrin-ZnO NPs, and deltamethrin-Ag NPs. In addition, the novel formulations of deltamethrin (deltamethrin-ZnO NPs and deltamethrin-Ag NPs) against Rhipicephalus (Boophilus) annulatus were also evaluated by in vivo animal efficacy trials. Nanoparticles and their loaded forms, deltamethrin-Ag NPs and deltamethrin-ZnO NPs, were characterized by Transmission Electron Microscope (TEM) and Fourier-Transform Infrared Spectrum (FTIR). The adulticidal activity of deltamethrin-ZnO NPs at different concentrations; 2 mL/L, 1 mL/L, 0.5 mL/L and 0.25 mL/L induced a significant (P ≤ 0.05) lethal effect on adult ticks compared to deltamethrin-Ag NPs at the same concentrations. The larvicidal efficacy of deltamethrin-ZnO NPs resulted in a complete larval mortality within 24 h of exposure, while deltamethrin and deltamethrin-Ag NPs exhibited 100% immobility of larvae 48 h post-exposure. Furthermore, the in vivo experiments showed a considerable reduction in the tick's survival after using deltamethrin-ZnO NPs. There was no significant effect of different treatments on liver or kidney function tests at pre- and post-treatment of animals. In conclusion, deltamethrin-ZnO nanocomposite was the most effective adulticide and larvicide against R. (B.) annulatus. To the best of our knowledge, this is the first report for using deltamethrin-ZnO NPs as an acaricide.

Synthetic pyrethroid resistance in Rhipicephalus (Boophilus) microplus ticks from north-western Himalayas, India

In the present study, adult immersion test (AIT) was used for evaluation of resistance against synthetic pyrethroids (deltamethrin and cypermethrin) in Rhipicephalus (Boophilus) microplus ticks collected from nine districts of three agro-climatic zones of north-western Himalayan region of India. Resistance factors (RFs) were calculated between 0.94 to 50.71 for deltamethrin and 0.32 to 13.18 for cypermethrin. Resistance to deltamethrin was detected at level I in two, level II in four, level III and level IV in one isolate each while one isolate was susceptible. Against cypermethrin, resistance at levels I and II was detected in three isolates each while three isolates were found susceptible. The low altitude sub-tropical zone revealed higher density of resistant ticks where intensive animal husbandry practices were followed and the synthetic pyrethroid usage was common. Data generated on pyrethroid resistance status of ticks in north-western Himalayan region will provide new insights in acaricidal resistance particularly from remote areas of this region and will help in formulating suitable control measures.

In vitro acaricidal activity of Piper nigrum and Piper longum fruit extracts and their active components against Rhipicephalus (Boophilus) microplus ticks

In vitro acaricidal activity of Piper nigrum and P. longum fruit extracts and their active components (piperine for P. nigrum and piperine and piperlonguminine for P. longum) was evaluated against adults engorged females of Rhipicephalus (Boophilus) microplus using adult immersion test. Three concentrations of each extract with four replications were used in the bioassay. Extracts significantly affected mortality rates of ticks in dose-dependent manner ranged 12.5-95.8% for P. nigrum and 29.2-87.5% for P. longum, with an additional effect on the reproductive physiology of ticks by inhibiting oviposition (28.1-96.9% by P. nigrum and 36.1-89.3% by P. longum). However, the acaricidal and oviposition limiting properties were decreased significantly when the active component(s) of each extract was tested separately. However, the combination of piperine and piperlonguminine (obtained from P. longum extract) caused 79.2% mortality of ticks which is equivalent to the corresponding concentration (~ 5%) of the extract. It can be concluded that the fruit extracts of P. nigrum and P. longum had both acaricidal and oviposition limiting actions against the adults of R. (B.) microplus which could make it a valuable component of developing sustainable strategy for integrated tick management.

Molecular mechanism of synthetic pyrethroid and organophosphate resistance in field isolates of Rhipicephalus microplus tick collected from a northern state of India

The frequently used chemical control method to manage Rhipicephalus microplus is limited by the emergence of resistance populations. Understanding of resistance mechanisms is essential to develop strategy for sustainable management. The present study was focused on working out the molecular mechanisms of resistance against synthetic pyrethroids (SPs) and organophosphates (OPs) in field isolates of R. microplus collected from six districts of Uttar Pradesh, India. Adult immersion test with discriminating concentrations (AIT-DC) was used to determine resistance status of isolates to SPs (deltamethrin, cypermethrin) and OPs (diazinon, coumaphos). All the six isolates were found resistant to SPs with resistance factor (RF) of 2.9-58.6 and to one of the OP compounds, diazinon having RF of 3.5-13.7 but susceptible to coumaphos (RF < 1.4). Three R. microplus genes, viz. para-sodium channel domain II S4-5 linker, carboxylesterase (372 bp) and acetylcholinesterase 2 (1692 bp) were sequenced and compared with respective sequences of reference susceptible IVRI-I, reference OP resistant population (IVRI-III), IVRI-IV and multi-acaricide resistant population (IVRI-V) of R. microplus. A C190A mutation in the domain II S4-5 linker region of sodium channel gene leading to L64I amino acid substitution was detected in all six isolates. The G1120A mutation in the carboxylesterase gene could not be detected in any isolate. Five nucleotide substitutions viz., G138A, G889A, T1090A, C1234T and G1403A were identified in the acetylcholinesterase 2 gene leading to four amino acid substitutions. The findings of the study corroborate the role of mutation in sodium channel and acetylcholinesterase 2 genes in SP and OP resistance in this part of India.

Molecular detection of Rhipicephalus (Boophilus) annulatus resistance against deltamethrin in middle Egypt

This study was designed to investigate the susceptibility/resistance of Rhipicephalus (Boophilus) annulatus to commercial deltamethrin 5%. The work was based on in vitro bioassays; adult immersion test (AIT) and larval packet test (LPT). Fully engorged female ticks were collected from 11 locations in Beni-Suef Governorate, Egypt (Alfashin, Eminelaros, Ehnasia, Smusta, Belifia, Aldiabia, Alhalabia, Beshnna, Alkom, Nasr and Beba). Two concentrations of commercial deltamethrin 5% (200 and 400 ppm) were tested by AIT on R. (B.) annulatus. The mortality of ticks at 400 ppm was higher than 200 ppm which was not reached to 100%. Ehnasia tick population was the least susceptible to deltamethrin while Alfashin population was the most susceptible one. Different deltamethrin concentrations (0.000625, 0.00125, 0.0025, 0.005, 0.010 and 0.020) were used in LPT to evaluate the larval mortality. The highest LC₅₀ appeared in Ehanasia tick population (0.01) with 95% confidence interval (0.005 to 0.01) meanwhile, the lowest LC₅₀ appeared in Alfashin (0.0006) with 95%CI (0.0005 to 0.0007). Thus, it is possible to deduce that one population was considered susceptible; seven populations were resistant level I and three populations were resistant level II. Additionally, PCR revealed that the resistant alleles (R) appeared in two localities (Ehnasia and Aldiabia). It was concluded that at least two tick populations of the investigated locations were of possible resistant to deltamethrin.

In vitro efficacy of amitraz, coumaphos, deltamethrin and lindane against engorged female Rhipicephalus (Boophilus) annulatus and Haemaphysalis bispinosa ticks

The present study compares the in vitro efficacy of four chemical acaricides, viz. amitraz, coumaphos, deltamethrin and lindane, against Rhipicephalus (Boophilus) annulatus and Haemaphysalis bispinosa ticks based on adult immersion tests. Amitraz, at 350 ppm, elicited 29.2 ± 4.17% mortality against R. (B.) annulatus, 100% inhibition of fecundity and absence of hatching of eggs laid by treated ticks. The same compound at 300 ppm caused 62.5 ± 12.5% mortality against H. bispinosa, 96.7% inhibition of fecundity and complete blocking of eclosion. The LC₅₀ value of amitraz against susceptible H. bispinosa was 181 ppm. Deltamethrin at 400 ppm, elicited 25.0 ± 4.81% adult R. (B.) annulatus mortality, 97.5% inhibition of fecundity and absence of egg hatching. Complete blocking of egg hatching was observed even at 30 ppm. However, deltamethrin (at 50 ppm) elicited 75.0 ± 10.76% mortality against H. bispinosa, 65.8% inhibition of fecundity and very low egg hatching (10%). The LC₅₀ for deltamethrin against susceptible H. bispinosa was 33.8 ppm. Coumaphos at 50 ppm, caused mortality of 70.8 ± 4.17% with R. (B.) annulatus whereas 100% mortality was observed against H. bispinosa. The LC₅₀ values of coumaphos against R. (B.) annulatus and H. bispinosa were 9 and 8.75 ppm, respectively. Complete inhibition (100%) of fecundity was observed even at 30 ppm against both parasites. Complete blocking of egg hatching was also observed even at 10 ppm of coumaphos. Lindane at 1000 ppm caused mortality of 87.5 ± 7.98% against R. (B.) annulatus and 83.3% mortality against H. bispinosa at 100 ppm. The LC₅₀ values of lindane against R. (B.) annulatus and H. bispinosa were 157 and 8.61 ppm, respectively. Complete inhibition of fecundity was observed with R. (B.) annulatus treated with lindane above 200 ppm and with H. bispinosa at a concentration above 50 ppm. Complete blocking of egg hatching was observed in R. (B.) annulatus, even at 100 ppm. Lindane caused 100% blocking of egg hatching at 1 ppm in the case of H. bispinosa.