Resistencia de la garrapata Boophilus microplus a los ixodicidas

Widespread acaricide resistance and multi-resistance in Rhipicephalus microplus in Ecuador and associated environmental and management risk factors

Rhipicephalus microplus is a cattle tick widely distributed in tropical and subtropical areas. Various acaricides are used and applied to control the ticks, but resistance is common. The objectives of this study were to evaluate the spatial distribution of resistance to the most commonly applied acaricides (amitraz, ivermectin, and alpha-cypermethrin) in ticks and assess potential risk factors associated with tick resistance in a strip between ±0.5° latitude of the continental part of Ecuador. Larval package tests were used to evaluate the level of acaricide resistance in 96 cattle farms. The association between 11 farm management and 8 ecological variables and acaricide resistance and multi-resistance was evaluated. Dose-response models were used to study the level of resistance. 72 % (69/96), 70 % (67/96), and 64 % (61/96) of farms had ticks resistant to amitraz, ivermectin, and alpha-cypermethrin, respectively. Multi-resistance was also widespread. Larger herds and dairy farms had a significantly higher probability of resistance for three commonly used acaricides. Environmental factors related to rainfall were also associated with acaricidal resistance presence. Ivermectin resistance was associated with use of the acaricide (OR = 8.9909; 7.7519-10.2300), mean temperature (OR = 1.3205;1.0742-1.6799)), and inversely associated with paddock rotation (OR = 0.1753; 0.0294-0.7836), and precipitation of the wettest month (BIO13) (OR = 0.9903; 0.9839-0.9957); amitraz with use of the acaricide (OR = 4.3934; 3.3679-5.4188), precipitation seasonality (BIO15) (OR=0.9742; 0.9542-0.9925), and precipitation (OR = 0.9995; 0.9994-0.9999); and alpha-cypermethrin with precipitation (OR=0.9995; 0.9990-0.9999) and use of the acaricide (OR = 14.4597; 13.4343-15.4852). In conclusion, acaricide resistance was widespread in our study area. Better-integrated tick management and environmentally friendly control strategies are required to reduce the use of acaricides while limiting tick-associated damage in herds.

Ixodicidal effect of extracts from Cordia boissieri, Artemisia ludoviciana and Litchi chinensis on Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

The ixodicidal activity of the methanolic extracts of Artemisia ludoviciana (Astereceae), Cordia boissieri (Boraginaceae) and Litchi chinensis (Sapindaceae) against two field populations of Rhipicephalus (Boophilus) microplus from the state of Nuevo Leon (NL) and Veracruz (VER) was evaluated. The extract of L. chinensis in the concentration of 150 mg/ml showed efficacies of 100% and 99% against engorged females and mortalities of 98% and 99% against larvae. C. boissieri in the same concentration showed efficacies of 71% and 37% against engorged adults and mortalities of 33.04% and 10.33% against larvae and A. ludoviciana had efficacies of 94% and 83% in adults and mortalities of 89.39% and 89.21% against larvae in both populations respectively. The enzymatic activity of Acetylcholinesterase (AChE), Carboxylesterase (CaE), Glutathione-S-Transferase (GST) and Alkaline Phosphatase (ALP) was measured in both populations of ticks. As a result, a significant difference between both populations was shown, being the VER population the one that exhibited a higher enzymatic activity (p ≤ 0.05). It can be concluded that the methanolic extract of the seed of L. chinensis shows potential ixodicidal activity and can be used as an alternative source of tick control, however, prior characterization, toxicity and formulation studies are necessary.

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.

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.

Acaricidal and Repellent Effects of Essential Oils against Ticks: A Review

Tick control is a priority in order to prevent the transmission of vector-borne diseases. Industrial chemical acaricides and repellents have been the most efficient tools against hard ticks for a long time. However, the appearance of resistances has meant the declining effectiveness of the chemicals available on the market. The trend today is to develop alternative control methods using natural products to replace nonefficient pesticides and to preserve the efficient ones, hoping to delay resistance development. Traditional in vitro evaluation of acaricidal activity or resistance to synthetic pesticides have been reviewed and they mainly focus on just one species, the one host tick (Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)). Recent reports have called for the standardization of natural product components, extraction techniques, and experimental design to fully discover their acaricidal potential. This study reviews the main variables used in the bibliography about the efficiency of natural products against ticks, and it proposes a unification of variables relating to ticks, practical development of bioassays, and estimation of ixodicidal activity.

In vivo and in vitro apoptosis induced by new acaricidal ethyl-carbamates in Rhipicephalus microplus

The ability of ethyl-4-bromophenylcarbamate (LQM 919) and ethyl-4-chlorophenylcarbamate (LQM 996) to induce in vivo apoptosis of Rhipicephalus microplus ovarian cells and in vitro apoptosis of tick and mammalian cell culture was evaluated. The ovaries of engorged females treated with 1 mg mL^-1 LQM 919 or LQM 996 presented more (p < 0.001) peroxidase-TUNEL-positive labeled cells (apoptotic cells) in situ than their respective control groups, and this increase was time-dependent (p < 0.001). The majority of apoptotic cells were observed in the epithelium and ovarian pedicel. HepG2, Vero and Rm-sus cells, as well as cells from primary cultures of R. microplus salivary glands, intestine and ovaries were exposed to different concentrations of the ethyl-carbamates. Both ethyl-carbamates induced a concentration-dependent reduction in the viability of all cell types (p < 0.001). Exposure to the ethyl-carbamates increased caspase 3 activity (p < 0.01) in primary cultures and cell lines, except in HepG2 cells. Fluorescent TUNEL-positive cells were observed in all cell types treated with 600 μM LQM 919 or LQM 996. These results indicate that both ethyl-carbamates induce apoptosis of the ovarian, intestinal and salivary glands cells in R. microplus and strongly suggest that this is their main mechanism of acaricidal action.

Genetic diversity of Bm86 sequences in Rhipicephalus (Boophilus) microplus ticks from Mexico: analysis of haplotype distribution patterns

Background

Ticks are a problem for cattle production mainly in tropical and subtropical regions, because they generate great economic losses. Acaricides and vaccines have been used to try to keep tick populations under control. This has been proven difficult given the resistance to acaricides and vaccines observed in ticks. Resistance to protein rBm86-based vaccines has been associated with the genetic diversity of Bm86 among the ectoparasite’s populations. So far, neither genetic diversity, nor spatial distribution of circulating Bm86 haplotypes, have been studied within the Mexican territory. Here, we explored the genetic diversity of 125 Bm86 cDNA gene sequences from R. microplus from 10 endemic areas of Mexico by analyzing haplotype distribution patterns to help in understanding the population genetic structure of Mexican ticks.

Results

Our results showed an average nucleotide identity among the Mexican isolates of 98.3%, ranging from 91.1 to 100%. Divergence between the Mexican and Yeerongpilly (the Bm86 reference vaccine antigen) sequences ranged from 3.1 to 7.4%. Based on the geographic distribution of Bm86 haplotypes in Mexico, our results suggest gene flow occurrence within different regions of the Mexican territory, and even the USA.

Conclusions

The polymorphism of Bm86 found in the populations included in this study, could account for the poor efficacy of the current Bm86 antigen based commercial vaccine in many regions of Mexico. Our data may contribute towards designing new, highly-specific, Bm86 antigen vaccine candidates against R. microplus circulating in Mexico.

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.

Survey of acaricides resistance status of Rhipiciphalus (Boophilus) microplus collected from selected places of Bihar, an eastern state of India

Monitoring acaricide resistance in field ticks and use of suitable managemental practices are essential for controlling tick populations infesting animals. In the present study, the acaricide resistance status in Rhipicephalus (Boophilus) microplus ticks infesting cattle and buffaloes of five districts located in the eastern Indian state, Bihar were characterized using three data sets (AIT, Biochemical assays and gene sequences). Adult immersion test (AIT) was adopted using seven field isolates and their resistance factor (RF) was determined. Six isolates (DNP, MUZ, BEG, VSH, DRB and SUL) were found resistant to both deltamethrin and diazinon and except VSH all were resistant to cypermethrin. One isolate (PTN) was susceptible with a RF below 1.5. To understand the possible mode of resistance development, targeted enzymes and gene sequences of the para sodium channel and achetylcholinesterase 2 (AChE2) were analyzed. The esterase, monooxygenase and glutathione-S-transferase (GST) activity of reference susceptible IVRI-I line was determined as 2.47 ± 0.007 nmol/min/mg protein, 0.089 ± 0.0016 nmol/mg of protein and 0.0439 ± 0.0003 nmol/mg/min respectively, which increased significantly in the resistant field isolates. However, except esterases, the fold increase of monooxygenase (1.14-2.27 times) and GST (0.82-1.53 times) activities were not very high. A cytosine (C) to adenine (A) nucleotide substitution (CTC to ATC) at position 190 in domain II S4-5 linker region was detected only in one isolate (SUL) having RF of 34.9 and in the reference deltamethrin resistant line (IVRI-IV). However, the T2134A mutation was not detected in domain IIIS6 transmembrane segment of resistant isolates and also in reference IVRI-IV line despite of varying degree of resistance. The flumethrin specific G215T and the recently identified T170C mutations were also absent in domain II sequences under study. Four novel amino acid substitutions in AChE2 gene of field isolates and in organophosphate (OP) resistant reference IVRI-III line were identified which can possibly have a role in resistance development.

Integrated control of an acaricide-resistant strain of the cattle tick Rhipicephalus microplus by applying Metarhizium anisopliae associated with cypermethrin and chlorpyriphos under field conditions

The efficacy of the fungus Metarhizium anisopliae to control ticks has been shown in several in vitro experiments. However, few studies have been undertaken in field conditions in order to demonstrate the applicability of its use as a biological control of ticks and its combination with chemical acaricides. The aim of the present study was to evaluate the efficacy of M. anisopliae to control an acaricide-resistant strain of Rhipicephalus microplus under laboratory and field conditions. First, the compatibility of M. anisopliae strain (TIS-BR03) with commercial acaricides and its potential to control the cattle tick were evaluated in vitro. In general, acaricide treatments had mild effects on fungus viability. In the field experiment, the median of treatment efficacy with acaricide only, M. anisopliae only and combination of M. anisopliae with acaricide were 71.1%, 56.3% and 97.9%, respectively. There is no statistical difference between groups treated with M. anisopliae and acaricide alone. Thus, in this work we have demonstrated the applicability of M. anisopliae use associated or not with chemical acaricides on field conditions in order to control an acaricide-resistant strain of the cattle tick R. microplus.

First report of fluazuron resistance in Rhipicephalus microplus: a field tick population resistant to six classes of acaricides

The control of the cattle tick Rhipicephalus microplus is based mainly on the use of chemical acaricides, which has contributed to the emerging problem of selection of resistant tick populations. Currently, there are six main classes of acaricides commercially available in Brazil to control cattle ticks, with fluazuron, a tick growth regulator with acaricidal properties, being the only active ingredient with no previous reports of resistance. Ticks (designated the Jaguar strain) were collected in a beef cattle ranch located at Rio Grande do Sul state, Southern Brazil, after a complaint of fluazuron treatment failure. To characterise the resistance of this strain against acaricides, larval tests were performed and showed that the Jaguar strain was resistant to all of the drugs tested: cypermethrin (resistance ratio, RR=31.242), chlorpyriphos (RR=103.926), fipronil (RR=4.441), amitraz (RR=11.907) and ivermectin (3.081). A field trial was conducted to evaluate the efficacy of fluazuron treatment in heifers that had been experimentally infested with the Jaguar or a susceptible strain. Between 14 and 28 days after treatment, the average efficacy in cattle experimentally infested with the susceptible strain was 96%, while for the Jaguar strain the efficacy was zero. Additionally, the Jaguar strain response to fluazuron was evaluated in vitro using a modified adult immersion test (AIT) and the artificial feeding assay (AFA). With the AIT, 50 ppm of fluazuron inhibited 99% of larvae hatching in the susceptible strain (POA) and less than 50% in the Jaguar strain. Results of the AFA showed a larval hatching rate of 67% at 2.5 ppm of fluazuron with the Jaguar strain; conversely, only 3% of larvae of the susceptible strain hatched at the same fluazuron concentration. The results showed here demonstrated the first case of fluazuron resistance in R. microplus and the first tick population resistant to six classes of acaricides in Brazil.

A comparative study on cypermethrin resistance in Rhipicephalus (Boophilus) microplus and Hyalomma anatolicum from Punjab (India)

A study to evaluate cypermethrin resistance in Rhipicephalus (Boophilus) microplus and Hyalomma anatolicum collected from Muktsar and Mansa districts of Punjab state, India, was conducted by using adult immersion test (AIT). The regression graphs of probit mortality of ticks plotted against log values of concentrations of cypermethrin was utilized for the determination of slope of mortality, lethal concentration for 50% (LC50), and the resistance factor (RF). On the basis of the data generated on variables (mortality, egg mass weight, reproductive index, and percentage inhibition of oviposition), the resistance levels were categorized. Resistance to cypermethrin was categorized as level II and I in R. (B.) microplus collected from Muktsar and Mansa districts, respectively, whereas, H. anatolicum from both locations showed a susceptible status. The RF values of Muktsar and Mansa field samples of engorged R. (B.) microplus (5.48 and 2.18, respectively) were much higher as those of engorged H. anatolicum (1.12 and 0.82, respectively) indicating a lower level and slower rate of development of cypermethrin resistance in multi-host ticks. The data generated in the current study might be of immense help in formulating suitable control measures against ticks and tick-borne diseases of animals.

Eficacia de los extractos hidroalcohólicos de dos plantas sobre garrapatas adultas Rhipicephalus (Boophilus) microplus

Se determinó la eficacia del extracto natural de Verbena officinalis L. y de Ruta graveolens L. en el control in vitro de la garrapata adulta Rhipicephalus (Boophilus) microplus. El extracto de cada planta se obtuvo mediante la técnica de maceración. Para las pruebas, se utilizaron garrapatas adultas de dos tamaños (pequeñas y medianas), que fueron expuestas a los extractos de cada planta, utilizando la técnica de inmersión de garra­patas adultas. A las 24, 48, 72 y 96 h de exposición, se realizó la lectura de mortalidad, donde se tomó como mínimo eficaz una mortalidad de 60%. Las pruebas ini­ciales se realizaron con extractos puros y cuando éstos mostraban eficacia se procedía a realizar diluciones cre­cientes, hasta encontrar la concentración mínima eficaz. Las pruebas fueron realizadas en clima frío. El extracto de R. graveolens (ruda) mostró efectividad en garrapata pe­queña y mediana, sólo con el extracto puro; V. officinalis (verbena negra) mostró eficacia sobre garrapata pequeña y mediana en la dilución 5:10. V. officinalis mostró ma­yor eficacia y se observó que los mejores resultados se obtuvieron con las mayores concentraciones.

Survey of pyrethroids resistance in Indian isolates of Rhipicephalus (Boophilus) microplus: identification of C190A mutation in the domain II of the para-sodium channel gene

Monitoring acaricide resistance and understanding the underlying mechanisms are critically important in developing strategies for resistance management and tick control. Eighteen isolates of Rhipicephalus (Boophilus) microplus collected from four agro-climatic regions of India were characterized and the resistant data were correlated with bioassay results, esterase enzyme activities and with the presence/absence of point mutation in the para-sodium channel gene. The adult immersion test was standardized to assess the level of resistance and resistant factors (RF) in the range of 1.2-95.7 were detected. Out of eighteen isolates, three were categorized as susceptible (RF<1.4), five isolates at level I (RF=1.5-<5), eight at level II (RF=5.1-<25), and one isolate each at level III (RF=26-<40) and level IV (RF=>41). The esterase enzyme ratio and survival% of tick isolates was observed significantly (p<0.001) correlated with correlation coefficient (r) in α- and β-esterase activity. The correlation of determination (R(2)) for α- and β-esterase activity indicated that 73.3% and 55.3% data points of field isolates were very close to the correlation lines. For detection of point mutation, three sites (mutation in domain IIS6, T2134A mutation in domain IIIS6 and C190A mutation in domain IIS4-5 linker) of sodium channel gene were amplified and sequenced. Comparative sequence analysis identified a cytosine (C) to adenine (A) nucleotide substitution (CTC to ATC) at position 190 in domain II S4-5 linker region of para-sodium channel gene in six isolates and in reference deltamethrin resistant IVRI-IV line. The occurrence of mutation in the tick isolates having high resistance factor suggested that target site insensitivity and enhanced esterase activity is the possible mechanism of resistance to deltamethrin in the Indian isolates of R. (B.) microplus. These results also concluded that the mutation site in Indian tick isolates is similar to Australian and Brazilian tick isolates while it is different in tick isolates from Mexico and North America. This is the first report of occurrence of mutation in para-sodium channel gene of deltamethrin resistant Indian isolates of R. (B.) microplus.

First report of a Rhipicephalus microplus tick population multi-resistant to acaricides and ivermectin in the Mexican tropics

We document the presence of a Rhipicephalus microplus tick population resistant to acaricides (organophosphates (OP), synthetic pyrethroids (SP), amitraz) and macrocyclic lactones (ML) (ivermectin). Engorged females of R. microplus were collected from a cattle farm in Veracruz, Mexico, to evaluate acaricide and ivermectin resistance. The modified larval packet test (LPT) was used to detect OP (chlorpiriphos and diazinon) and SP (flumethrin, deltamethrin and cypermethrin) resistance and the larval immersion test (LIT) to detect resistance to amitraz and ivermectin. Both, LPT and LIT were performed twice at different times with different collected samples. Mortality data with ivermectin were subjected to probit analysis to obtain lethal concentrations and resistance ratios (RR) using an ivermectin-susceptible strain (Deutch) as a reference. The R. microplus population showed resistance to all acaricides tested, with different mortalities at the discriminate dose: chlorpiriphos (1%), diazinon (24.2%), flumethrin (92.8%), deltamethrin (94.2%), cypermethrin (98.0%) and amitraz (1.5%). The studied tick population also showed resistance to ivermectin with a resistance ratio at 99% of 9.58 and 6.52 in the first and second evaluation, respectively. We report for the first time a R. microplus population in Mexico with different levels of resistance to OP, SP, amidines (Am) and ivermectin. The uncontrolled use of these products in the study area may promote the complete failure of tick control within a short period of time.

A novel amino acid substitution in the para-sodium channel gene in Rhipicephalus microplus (Acari: Ixodidae) associated with knockdown resistance

Resistance acquired by the tick Rhipicephalus microplus (Canestrini) to different types of ixodicides in Mexico has had a negative impact on national and local livestock, mainly due to the transmission of diseases such as babesiosis and anaplasmosis, among others. The technique used for the diagnosis of resistance was that in the bioassays noted in the Norma Oficial Mexicana (NOM-006-ZOO-1994). The purpose of this investigation was the determination of resistance to pyrethroids through isoleucine-phenylalanine mutation in the gene KDR, in a population of ticks from Montemorelos, NL, Mexico. Preliminary bioassays demonstrated resistance to cypermethrin and deltamethrin (27.4%) and flumethrin (36.7-34.7%). To identify the mutation, DNA was extracted from 100 mg of larvae (pools), 10 pools were assessed by PCR, in which a pair of primers designed with the program Oligo 2.0 and Amplify 1.2 amplified a 136 bp fragment containing the mutation. The PCR product was subsequently sequenced to confirm the presence of the mutation. A strain susceptible to pyrethroid insecticides (Mora strain) was used as control, but it did not show the mutation. However, the mutation was detected in 4 out of 10 samples of the strain Montemorelos.

Laboratory and field evaluation of Metarhizium anisopliae (Deuteromycotina: Hyphomycetes) for the control of Rhipicephalus microplus (Acari: Ixodidae) in the Mexican tropics

The aim of the present study was to evaluate the effect of Metarhizium anisopliae to control Rhipicephalus microplus under laboratory and field conditions (larvae on vegetation) in the Mexican tropics. In the laboratory study, Ma34, Ma14 and a mixture of Ma34+Ma14 strains of M. anisopliae were evaluated for their control of the adult and larval stages of R. microplus, using the adult and larval immersion test respectively. The reproductive efficiency index of engorged females was determined in the treated and control groups. In the adults, the Ma34 and MA14 strains both produced an efficacy of 100% on engorged females at 1 x 10(8), 1 x 10(7) and 1 x 10(6)conidia/ml; however, only Ma34 killed 100% at 1 x 10(6)conidia/ml dose. The mixture of both strains (Ma34+Ma14) produced an efficacy of 100% on engorged females at 1 x 10(8)conidia/ml. R. microplus engorged females treated with Ma34 and a mixture of strains Ma34 and Ma14 reduced egg oviposition by 55.5% and 39.1% respectively compared to treated controls (P<0.001). In the larval evaluation, Ma14 produced an efficacy of 45-62%; however, Ma34+Ma14 increased the efficacy reaching 90% (1 x 10(8)conidia/ml concentrations, P<0.05). In the field study, twelve 9 m(2) plots with vegetation were artificially infested with R. microplus larvae. Six plots were used as control and six as test areas. The treated plots received the Ma34+Ma14 (1 x 10(8)conidia/ml) by manual scattering at 0, 14 and 28 days post-treatment (PT). The number of larvae in the treated and control group was determined at 0, 7, 14, 21, 28 and 35 days PT by the tick drag method. This field study was carried out in two different seasons (January-March, wet, April-May, dry). In the wet season trial the efficacy of M. anisopliae to control R. microplus was 67.7% and 100% in the dry season trial .In conclusion, the mixture of Ma34 and Ma14 strains of M. anisopliae showed a high efficacy to control both larval and adult stages of R. microplus under laboratory conditions, and in field conditions these strains were efficient to control larval stages on vegetation.