An investigation of the acaricidal activity of benzyl alcohol on Rhipicephalus annulatus and Rhipicephalus sanguineus and its synergistic or antagonistic interaction with commonly used acaricides.

The most economically significant ectoparasites in the tropics and subtropics are ixodid ticks, especially Rhipicephalus annulatus and Rhipicephalus sanguineus. Years of extensive use of the readily available acaricides have resulted in widespread resistance development in these ticks, as well as negative environmental consequences. Benzyl alcohol (BA) has been frequently used to treat pediculosis and scabies, and it may be an effective alternative to commonly used acaricides. The main aim of the present study was to evaluate the acaricide activity of BA and its combination with the regularly used chemical acaricides against R. annulatus and R. sanguineus. Different concentrations of BA alone and in combination with deltamethrin, cypermethrin and chlorpyrifos were tested in vitro against adult and larvae of both tick species. The results showed that BA is toxic to R. annulatus and R. sanguineus larvae, with 100% larval mortality at concentrations of ≥50 mL/L, and LC50 and LC90 attained the concentrations of 19.8 and 33.8 mL/L for R. annulatus and 18.8 and 31.8 mL/L for R. sanguineus, respectively. Furthermore, BA in combination with deltamethrin, cypermethrin and chlorpyrifos exhibited synergistic factors of 2.48, 1.26 and 1.68 against R. annulatus larvae and 1.64, 11.1 and 1.14 against R. sanguineus larvae for deltamethrin + BA, cypermethrin + BA and chlorpyrifos + BA, respectively. BA induced 100% mortality in adult R. annulatus at concentrations of ≥250 mL/L with LC50 and LC90 reached the concentrations of 111 and 154 mL/L, respectively. Additionally, BA had ovicidal activity causing complete inhibition of larval hatching at 100 mL/L. The combination of BA with deltamethrin and cypermethrin increased acetylcholinesterase inhibition, whereas the combination of BA with chlorpyrifos decreased glutathione (GSH) activity and malondialdehyde levels. In the field application, the combination of BA 50 mL/L and deltamethrin (DBA) resulted in a significant reduction in the percentage of ticks by 30.9% 28 days post-treatment when compared with groups treated with deltamethrin alone. In conclusion, BA causes mortality in laboratory and field studies alone and in combination with cypermethrin or deltamethrin. BA can be used for control of ticks of different life stages, that is, eggs and larvae, through application to the ground.

Alpha- and beta-pinene isomers act differently to control Rhipicephalus microplus (Acari: Ixodidae).

The cattle tick Rhipicephalus microplus is an ectoparasite of high importance in veterinary medicine and public health. Since synthetic chemicals used to control these ticks can select resistant strains and cause toxic effects in their hosts, there is a need to identify effective substances with fewer adverse effects. For this reason, we investigated the effects of alpha- and beta-pinene, known for their various biological effects, on the mortality and reproductive performance of R. microplus engorged female ticks. The products were diluted in a 2% Tween 80 aqueous solution. The ticks were first weighed and then immersed in the test solutions for five minutes. Then, they were dried with paper towels and fixed dorsoventrally in Petri dishes, totalling five treatment groups for each pinene and a control group treated with the solvent alone. The ticks were monitored daily for mortality, and their eggs were collected and weighed. The larval hatching rate was estimated, and the pre-oviposition and incubation periods were determined. From these data, the following parameters were calculated: egg production index, fertility rate, estimated reproduction rate, percentages of reduction in oviposition and hatching, and product efficacy. Alpha-pinene showed better results at higher concentrations, unlike beta-pinene, which was more effective at lower concentrations. The effectiveness of alpha-pinene was 74% at a concentration of 14.0 µL/mL, while beta-pinene showed 78% efficacy at 2.0 µL/mL. The results indicated for the first time different effects of two isomers in ticks, suggesting that these compounds act on R. microplus females in different ways.

Strategic control of the cattle tick Rhipicephlaus microplus applied to rotational and silvopastoral grazing systems in subtropical areas.

This work evaluated if strategic control based on no more than three or four annual treatments is useful to control Rhipicephalus microplus infestations on cattle when it is applied to intensive rotational grazing and silvopastoral systems with high stocking rates in subtropical areas. In the intensive rotational grazing system, three annual treatments with chemical acaricides were applied on cattle in two different schemes: between spring and early summer and from late winter and late spring. Strategic control based on three treatments with chemical acaricides from late winter to late spring plus an additional fourth treatment in summer was tested in the silvopastoral system. In the intensive rotational grazing systems, the control schemes allow to reach a significant reduction in the tick load on cattle considering a time interval from spring to autumn. However, the efficacy levels were not high enough in some specific moments, namely, the tick counts of summer and autumn (there were not significant differences between treated and control groups). The scheme evaluated in the silvopastoral grazing system yielded better results than those tested for the intensive rotational system, because significant differences in tick load between treated and control groups were observed in all post-treatment counts and when the analysis was performed for the whole study period. However, values of efficacy in the count-by-count comparison were disparate, ranging from 64.1 to 99.7. Although the efficacy values obtained in the silvopastoral system were better than those of the rotational grazing systems, the total tick load on treated cattle in autumn was not low enough (mean abundance values 25.14 and 38.14). Ticks were more evenly distributed among hosts in late summer and autumn than in spring or early summer, where few hosts carry most of the ticks. Some management strategies as intensive rotational systems or silvopastoral structures can lead to a more efficient forage use, but they imply greater tick challenge than in extensive grazing systems. In these situations, the schemes of strategic control bases on three or four annual treatments should be complemented with additional tactical treatments in late summer or autumn.

Metarhizium pingshaense photolyase expression and virulence to Rhipicephalus microplus after UV-B exposure.

The current study examined the impact of ultraviolet (UV)-B radiation in Metarhizium pingshaense blastospores' photolyase expression and their virulence against Rhipicephalus microplus. Blastospores were exposed to UV under laboratory and field conditions. Ticks were treated topically with fungal suspension and exposed to UV-B in the laboratory for three consecutive days. The expression of cyclobutane pyrimidine dimmers (CPDs)-photolyase gene maphr1-2 in blastospores after UV exposure followed by white light exposure was accessed after 0, 8, 12, 24, 36, and 48 h. Average relative germination of blastospores 24 h after in vitro UV exposure was 8.4% lower than 48 h. Despite this, the relative germination of blastospores exposed to UV in the field 18 h (95.7 ± 0.3%) and 28 h (97.3 ± 0.8%) after exposure were not different (p > 0.05). Ticks treated with fungus and not exposed to UV exhibited 0% survival 10 days after the treatment, while fungus-treated ticks exposed to UV exhibited 50 ± 11.2% survival. Expression levels of maphr1-2 8, 12, and 24 h after UV-B exposure were not different from time zero. Maphr1-2 expression peak in M. pingshaense blastospores occurred 36 h after UV-B exposure, in the proposed conditions and times analyzed, suggesting repair mechanisms other than CPD-mediated-photoreactivation might be leading blastospores' germination from 0 to 24 h.

What is the optimal timing to initiate strategic control of Rhipicephalus microplus in taurine cattle in a tropical region?

Cattle tick control poses a significant challenge for livestock in tropical and subtropical regions. The objective of this study was to determine the most suitable timing to initiate a strategic tick control program and to identify the ideal number of acaricide treatments for adult taurine cattle (Bos taurus taurus) in a tropical region throughout the year. Three groups with 10 bovines each were performed: T01 (strategic treatment in late autumn/winter/late spring, every 28 days), T02 (strategic treatment to act in the "first tick generation" - early spring/summer/early autumn, every 28 days) and T03 (control). Tick counts (females 4-8 mm) were conducted every 14 days. If the tick burden in any group reached 30 or more during these counts, we applied an additional treatment. Over the course of a year, T02 required significantly fewer (p < 0.05) acaricide treatments than T01, with nine treatments for T02 and eleven for T01. Furthermore, during the tick counts, animals in T02 showed a lower tick burden compared to those in T01. Initiating the strategic tick control program in early spring, corresponding to the first tick generation, proved more effective than starting in autumn. This approach not only required fewer acaricide treatments but also resulted in a reduced tick burden. These benefits are particularly valuable in terms of animal welfare and managing acaricide resistance issues.

Anaplasmosis outbreaks in taurine and zebu cattle in Brazil: causes, treatments, and Anaplasma marginale genetic diversity.

This study aimed to investigate seven outbreaks of A. marginale infection in two regions of Brazil, affecting taurine, zebu, and crossbred cattle. We assessed the possible causes, treatment measures, and genetic diversity of A. marginale. These outbreaks occurred in two states (Goiás: outbreaks 1-7; Mato Grosso do Sul: outbreak 3), breeds (Holstein, Nellore, and crossbreed), age groups (beef cattle: 18-25 days old and 7-8 months; dairy cattle: 18-25 days old, 13-14 months, and cow after the first birth) and rearing systems (feedlot, pasture, pen in a wood shaving bedding system and compost bedded-pack barns). Metaphylactic or prophylactic treatments varied according to outbreak (imidocarb dipropionate: outbreaks 1-4 and 6; enrofloxacin: outbreaks 5 and 7; diminazene diaceturate: outbreak 5). In outbreaks 6 and 7, the packed cell volume was monitored. In all outbreaks, the practice of needle/syringe sharing was discontinued. For outbreaks 1-3, clinical signs and mortality (range, 4.8-13.3%) occurred 36-45 days after entry into the feedlot. In outbreak 4, A. marginale was diagnosed in 66.2% of the calves (bacteremia, 0-4.5%), with a mortality of 8.6%. Among nursing calves aged 60 days during outbreak 5, 53.8% were infected with A. marginale, with average bacteremia of 2.7% (range, 0-21.3%), and a mortality of 13.8%. In dairy heifers aged 14 months, raised in paddocks lacking vegetation cover and infested with R. microplus, then transitioned to a rotational grazing system also infested with R. microplus, the A. marginale bacteremia ranged from 3.2 to 6.7%, with a mortality of 20%. Before monitoring during outbreak 7, the mortality was 17.9%, but no further deaths were observed after monitoring initiation. In conclusion, possible causes triggering the outbreaks included primary tick infestation, needle/syringe sharing, and stress factors which may have affected the immunological statues of animals in the feedlots. Control measures performed in all outbreaks were effective. The partial msp4 gene sequences of A. marginale generated herein belonged to two haplotypes, but further research would be needed to investigate if this finding has any clinical significance.

Worldwide comparison between the potential distribution of Rhipicephalus microplus (Acari: Ixodidae) under climate change scenarios.

The cattle tick Rhipicephalus microplus (Acari: Ixodidae) has demonstrated its ability to increase its distribution raising spatially its importance as a vector for zoonotic hemotropic pathogens. In this study, a global ecological niche model of R. microplus was built in different scenarios using Representative Concentration Pathway (RCP), Socio-Economic Pathway (SSP), and a climatic dataset to determine where the species could establish itself and thus affect the variability in the presentation of the hemotropic diseases they transmit. America, Africa and Oceania showed a higher probability for the presence of R. microplus in contrast to some countries in Europe and Asia in the ecological niche for the current period (1970-2000), but with the climate change, there was an increase in the ratio between the geographic range preserved between the RCP and SSP scenarios obtaining the greatest gain in the interplay of RCP4.5-SSP245. Our results allow to determine future changes in the distribution of the cattle tick according to the increase in environmental temperature and socio-economic development influenced by human development activities and trends; this work explores the possibility of designing integral maps between the vector and specific diseases.

Acaricidal activity of a 2-methoxy-clovan-9-ol rich fraction from Eugenia copacabanensis (Myrtaceae) extract on Rhipicephalus microplus (Acari: Ixodidae).

Rhipicephalus microplus (Ixodidae, canestrini, 1888) is an invasive ectoparasite of cattle which causes high economic losses in emerging countries such as Brazil. Phytochemical compounds have been tested as an alternative to synthetic acaricides due to potentially lower mammalian toxicity. This study evaluated the acaricidal activity against R. microplus of the 2-methoxy-clovan-9-ol rich fraction obtained from Eugenia copacabanensis Kiaersk.leaves, a little known Myrtaceae species from the Brazilian Atlantic Forest. This fraction was obtained by maceration with methanol, partition with n-hexane and purification by normal-phase column chromatography. GC-MS, 1H and 13C NMR and IR analysis contributed to the identification of a major compound as the sesquiterpene 2-methoxy-clovan-9-ol, reported for the first time for the Myrtaceae family. The fraction was tested against R. microplus unfed larvae and engorged females and a 93% larval mortality was observed at the concentration of 50 mg mL-1. Lower concentrations of the solution tested demonstrated a significant difference in egg mass weight, hatching and control percentage. Experiments with 50.0 mg mL-1 showed significative results, with lower concentration and maximum efficacy for both assays. The IC50 values for unfed larvae and engorged females were 21.76 and 11.13 mg mL-1, respectively. These results were similar to those obtained in other studies with isolated botanical compounds and essential oils. The lower IC50 for engorged females than for unfed R. microplus larvae had also been described for other plant materials, including plants from the same Myrtaceae family. The present result suggested different mechanisms of action of the compound on the reproductive biology of engorged females, improving its effect against egg viability. These results are important for tick control, suggesting that 2-methoxy-clovan-9-ol could be a potential natural acaricidal product against both R. microplus unfed larvae and engorged females.

Analysis of the bacterial community in female Rhipicephalus microplus ticks from selected provinces in Luzon, Philippines, using next-generation sequencing.

Analysis of the tick microbiome can help understand tick-symbiont interactions and identify undiscovered pathogens, which may aid in implementing control of ticks and tick-borne diseases. The tropical cattle tick Rhipicephalus microplus is a widespread ectoparasite of cattle in the Philippines, negatively affecting animal productivity and health. This study characterized the bacterial community of R. microplus from Luzon, Philippines, through next-generation sequencing of 16s rRNA. DNA was extracted from 45 partially engorged female ticks from nine provinces. The DNA samples were pooled per province and then sequenced and analyzed using an open-source bioinformatics platform. In total, 667 operational taxonomic units (OTUs) were identified. The ticks in all nine provinces were found to have Coxiella, Corynebacterium, Staphylococcus, and Acinetobacter. Basic local alignment search tool (BLAST) analysis revealed the presence of known pathogens of cattle, such as Bartonella, Ehrlichia minasensis, and Dermatophilus congolensis. The tick samples from Laguna, Quezon, and Batangas had the most diverse bacterial species, whereas the tick samples from Ilocos Norte had the lowest diversity. Similarities in the composition of the bacterial community in ticks from provinces near each other were also observed. This is the first study on metagenomic analysis of cattle ticks in the Philippines, providing new insights that may be useful for controlling ticks and tick-borne diseases.

Transcriptional changes in the peripheral blood leukocytes from Brangus cattle before and after tick challenge with Rhipicephalus australis.

BACKGROUND: Disease emergence and production loss caused by cattle tick infestations have focused attention on genetic selection strategies to breed beef cattle with increased tick resistance. However, the mechanisms behind host responses to tick infestation have not been fully characterised. Hence, this study examined gene expression profiles of peripheral blood leukocytes from tick-naive Brangus steers (Bos taurus x Bos indicus) at 0, 3, and 12 weeks following artificial tick challenge experiments with Rhipicephalus australis larvae. The aim of the study was to investigate the effect of tick infestation on host leukocyte response to explore genes associated with the expression of high and low host resistance to ticks. RESULTS: Animals with high (HR, n = 5) and low (LR, n = 5) host resistance were identified after repeated tick challenge. A total of 3644 unique differentially expressed genes (FDR < 0.05) were identified in the comparison of tick-exposed (both HR and LR) and tick-naive steers for the 3-week and 12-week infestation period. Enrichment analyses showed genes were involved in leukocyte chemotaxis, coagulation, and inflammatory response. The IL-17 signalling, and cytokine-cytokine interactions pathways appeared to be relevant in protection and immunopathology to tick challenge. Comparison of HR and LR phenotypes at timepoints of weeks 0, 3, and 12 showed there were 69, 8, and 4 differentially expressed genes, respectively. Most of these genes were related to immune, tissue remodelling, and angiogenesis functions, suggesting this is relevant in the development of resistance or susceptibility to tick challenge. CONCLUSIONS: This study showed the effect of tick infestation on Brangus cattle with variable phenotypes of host resistance to R. australis ticks. Steers responded to infestation by expressing leukocyte genes related to chemotaxis, cytokine secretion, and inflammatory response. The altered expression of genes from the bovine MHC complex in highly resistant animals at pre- and post- infestation stages also supports the relevance of this genomic region for disease resilience. Overall, this study offers a resource of leukocyte gene expression data on matched tick-naive and tick-infested steers relevant for the improvement of tick resistance in composite cattle.

Molecular targets for the development of new acaricides against Rhipicephalus microplus: a review.

The cattle tick Rhipicephalus microplus is an ectoparasite with high economic importance to bovine culture, mainly in tropical and subtropical regions. The resistance of the tick from the commercial acaricides has hindered its control, thus motivating the search for new strategies. The purpose of this study was to perform a critical review about the main molecular targets of R. microplus that are useful for the discovery of new acaricides. Bibliographic search was conducted in the databases PubMed, ScienceDirect and CAB Direct, using the following descriptors: 'Rhipicephalus microplus', 'Boophilus microplus', 'molecular targets' and 'action', published between 2010 and 2021. Out of the 212 publications identified, 17 articles were selected for study inclusion. This review described 14 molecular targets and among these 4 are targets from commercial acaricides. Most of them are enzymes to catalyse important reactions to tick survival, related to energetic metabolism, mechanisms of biotransformation and neurotransmission. The data will be helpful in the development of new more effective and selective acaricides.

Effect of the formulation with fipronil and fluazuron on the reproductive biology and ovaries histopathology of Rhipicephalus microplus engorged females.

This study aimed to evaluate the effects of a commercial formulation containing fipronil and fluazuron on the reproductive biology and the morphology of ovaries from Rhipicephalus microplus engorged females. To carry out the study, three calves were artificially infested every 3 days with approximately 5000 larvae. On day 0, the animals were treated with a commercial formulation containing fipronil (1.25 mg/kg) + fluazuron (2.5 mg/kg). Before the application of the acaricide, engorged females of R. microplus were collected to constitute the control group (10 for biology analyses and 20 for histology analyses). After applying the commercial formulation, naturally detached engorged females were recovered on days + 5, + 10, and + 20 (10 engorged females/day) to evaluate their reproductive biology, and on days + 4, + 12, and + 20 (20 engorged females/day) for histological evaluation of the ovaries. Females from the treated groups produced smaller amounts of eggs, exhibiting lower viability when compared to eggs from the control group (p < 0.05). The ovaries of females from all treated groups (+ 4, + 12, and + 20) showed morphological changes, including: cytoplasmic disorganization, cytoplasmic degradation, irregular shape of the oocyte and germinal vesicle, reduction and vacuolization of yolk granules and oocyte disruption. Oocytes were observed in smaller numbers in all stages of development (I, II, III, IV, and V) and greater numbers of indeterminate oocytes were verified in the ovaries of the treated groups when compared to the control group. Therefore, results showed that the commercial formulation containing fipronil and fluazuron affected the reproductive biology, caused morphological changes in the ovaries, and reduced the number of oocytes in R. microplus engorged females.

Resistance of the cattle tick Rhipicephalus (Boophilus) microplus to fluazuron in Argentina.

The aim of this work is to report the presence of resistance to fluazuron in a population of Rhipicephalus microplus in Argentina. The evidence was obtained from field and in vitro trials. In the field trial, cattle infested with ticks was treated with two commercial formulations of fluazuron. The in vitro trial (adult immersion test, AIT) was performed by using technical grade fluazuron. In the field trial, there were no significant differences between the treated and control groups between days 2 and 34 post-treatment. The only exceptions (treated group I in day 14 post-treatment, treated group II in days 23 and 29 post-treatment) had a significantly lower tick load than the untreated group, but the efficacy was not higher than 70%. Viable engorged females were collected on both groups of treated bovines in all counts, and the production of viable larvae was not precluded with the application of the two commercial formulations of fluazuron evaluated in this study. The results obtained with the in vitro assay (AIT) also indicate that the R. microplus population tested in this work has a higher level of resistance to fluazuron than another susceptible field strain. The integrated analysis of the field and in vitro trials clearly reveals the emergence of resistance to fluazuron in a R. microplus population from Argentina. This diagnosis of resistance does not imply that the fluazuron has lost its functionality at a regional scale, but it highlights the need to establish control strategies that minimize the use of this drug in order to preserve its functionality as an acaricide.

Phenotypic and Target-Directed Screening Yields New Acaricidal Alternatives for the Control of Ticks.

Rhipicephalus microplus, the "common cattle tick", is the most important ectoparasite in livestock worldwide due to the economic and health losses it produces. This tick is a vector for pathogens of several tick-borne diseases. In Latin American countries, damages reach approximately USD 500 million annually due to tick infections, as well as tick-borne diseases. Currently, resistant populations for every chemical group of acaricides have been reported, posing a serious problem for tick control. This study aims to find new alternatives for controlling resistant ticks with compounds derived from small synthetic organic molecules and natural origins. Using BME26 embryonic cells, we performed phenotypic screening of 44 natural extracts from 10 Mexican plants used in traditional medicine, and 33 compounds selected from our chemical collection. We found 10 extracts and 13 compounds that inhibited cell growth by 50% at 50 µg/mL and 100 µM, respectively; the dose-response profile of two of them was characterized, and these compounds were assayed in vitro against different life stages of Rhipicephalus microplus. We also performed a target-directed screening of the activity of triosephosphate isomerase, using 86 compounds selected from our chemical collection. In this collection, we found the most potent and selective inhibitor of tick triosephosphate isomerase reported until now. Two other compounds had a potent acaricidal effect in vitro using adults and larvae when compared with other acaricides such as ivermectin and Amitraz. Those compounds were also selective to the ticks compared with the cytotoxicity in mammalian cells like macrophages or bovine spermatozoids. They also had a good toxicological profile, resulting in promising acaricidal compounds for tick control in cattle raising.

Cross-resistance between macrocyclic lactones in populations of Rhipicephalus microplus in Brazil's semiarid region.

Rhipicephalus microplus, also known as the cattle tick, is the parasite with the greatest impact on cattle in Brazil. The most common method for controlling this tick is the application of synthetic chemical acaricides, especially ivermectin, which belongs to the group of macrocyclic lactones (MLs). However, because ivermectin is widely used, there is concern about the development of cross-resistance within this chemical class. Thus, engorged females were collected from farms with a history of resistance to ivermectin, which was the only one among the MLs that was used as an endectocide drug. Using larval immersion tests (LIT), bioassays were performed with ivermectin, moxidectin and eprinomectin on populations of R. microplus from the semiarid region of the states of Paraíba and Ceará, Brazil. Epidemiological questionnaires were applied to collect information about tick control management. All the evaluated populations showed cross-resistance between ivermectin and moxidectin, but only one population showed cross-resistance between ivermectin and eprinomectin. Weekly or monthly administration of injectable 1% ivermectin on farms was reported. It was concluded that the frequent use of ivermectin may lead to the development of cross-resistance to moxidectin. For eprinomectin, despite the structural similarity, cross-resistance was not observed in three tick populations.

Combination of synthetic acaricides with (E)-cinnamaldehyde to control Rhipicephalus microplus.

This work had the objectives to (1) evaluate the susceptibility of various Rhipicephalus microplus populations to commercial acaricides, and (2) select commercial acaricides (50-80% effective) and evaluate the effects of binary combinations of the phenylpropanoid (E)-cinnamaldehyde with selected commercial acaricides to control R. microplus under laboratory and field conditions. Using adult immersion tests with 116 populations and 14 commercial acaricides, products showing 50-80% effectiveness (percent control) with the lowest number of active ingredients were selected. Acaricides containing amitraz or chlorfenvinphos were tested in combination with (E)-cinnamaldehyde on a field population (strain CM). We found that (E)-cinnamaldehyde enhanced the activity of both commercial acaricides against R. microplus larvae; however, the enhancement was more accentuated when using amitraz. Experiments combining (E)-cinnamaldehyde + amitraz on unfed larvae and engorged females from another population (strain Gyn) were performed, verifying (E)-cinnamaldehyde enhanced the activity of amitraz. In the field experiment, the application of (E)-cinnamaldehyde appeared toxic to the tick hosts (cattle). We concluded that (E)-cinnamaldehyde enhanced the activity of amitraz against unfed larvae and engorged females of R. microplus; however, in the field test this phenylpropanoid caused intoxication in the cattle. Studies searching for new combinations of compounds from essential oils with amitraz deserve attention, as well as studies to develop formulations using amitraz + (E)-cinnamaldehyde that will be efficient and will not have toxic effects in cattle.

Inorganic pellets containing microsclerotia of Metarhizium anisopliae: a new technological platform for the biological control of the cattle tick Rhipicephalus microplus.

This study was sought to devise pellets containing inorganic materials and microsclerotia of Metarhizium anisopliae strain IP 119 for biological control of Rhipicephalus microplus, the most economically important tick in Brazilian cattle industry. In addition, we evaluated the storage stability of the pellets, their tolerance to ultraviolet radiation (UV-B), and efficacy against ticks under laboratory conditions. Fungal microsclerotia were produced by liquid culture fermentation and mixed with pre-selected inorganic matrices: vermiculite powder, diatomaceous earth, and colloidal silicon dioxide (78:20:2, w/w/w). The microsclerotial pellets were then prepared by a two-stage process involving extrusion and spheronization. Pellet size averaged 525.53 ± 7.74 µm, with a sphericity index of 0.72 ± 0.01, while biomass constituents did not affect the wet mass properties. Conidial production from microsclerotial pellets upon rehydration ranged from 1.85 × 109 to 1.97 × 109 conidia g-1 with conidial viability ≥ 93%. Conidial production from pellets stored at 4 °C was invariable for up to 21 days. Unformulated microsclerotia and microsclerotial pellets were extremely tolerant to UV-B compared with aerial conidia. Engorged tick females exposed to conidia from sporulated pellets applied to soil samples and upon optimal rehydration exhibited shorter oviposition time length, shorter life span, and reduced number of hatched larvae. In summary, microsclerotial pellets of M. anisopliae IP 119 effectively suppressed R. microplus and showed outstanding UV-B tolerance in laboratory tests. Prospectively, this formulation prototype is promising for targeting the non-parasitic stage of this tick on outdoor pasture fields and may offer a novel mycoacaricide for its sustainable management. KEY POINTS: • Pellets with microsclerotia and inorganic materials are innovative for tick control. • Metarhizium microsclerotia show superior UV-B tolerance in relation to conidia. • Pellets of Metarhizium microsclerotia produce infective conidia against ticks.

Integrated control of the cattle tick, Rhipicephalus australis (Acari: Ixodidae), in New Caledonia through the Pasture and Cattle Management method.

Development of the Pasture and Cattle Management (PCM) method is a priority to control the cattle tick, Rhipicephalus australis, in New Caledonia. The PCM method provides the foundation for sustainable integrated tick control because approximately 95% of cattle ticks in infested pastures are off the host in the non-parasitic life stages, and the practice of treating cattle intensely with chemical acaricides is a risk for the emergence of resistance to these active ingredients in commercial acaricidal products available for veterinary use. Here, we report the findings of an assessment survey to document the utility of the PCM method. Analyses of questionnaire data provided by 21 beef cattle producers describing their management of 37 herds informed how to (1) assess the ability of PCM to reduce acaricide use and (2) prioritize best practices and define recommendations to breeders promoting efficient tick control with minimum acaricide use. Boosted regression tree analysis showed a significant (p = 0.002) reduction of ≈33% in the number of acaricide treatments from 7.9 to 5.3 per year by using PCM. Of the 24 factors identified as potentially affecting acaricide use, six factors accounted for ≈86% of the variability in number of acaricide treatments applied annually. The six most influential factors involved farm characteristics as well as pasture and herd management recommendations. These results demonstrated the usefulness of PCM for integrated control of R. australis infestations while reducing acaricide use to improve cattle production in New Caledonia.

Determination of resistance status to amitraz in the cattle tick Rhipicephalus (Boophilus) microplus from Luzon, Philippines, through bioassay and molecular analysis.

Tick infestations and tick-borne diseases are among the leading causes of economic losses in the cattle industry worldwide. Amitraz is one of the most commonly used chemical acaricides against the cattle tick Rhipicephalus (Boophilus) microplus. Resistance to amitraz has been reported in many countries but not in the Philippines. This study aimed to determine whether cattle ticks from provinces in northern and southern Luzon, Philippines, are resistant to amitraz. Engorged or nearly engorged female ticks were collected from 21 farms and allowed to lay eggs to produce larvae. Larval packet test (LPT) was performed using three concentrations of amitraz, as well as a negative control (diluent). Reverse-transcription polymerase chain reaction (RT-PCR) was also performed to amplify a fragment of the octopamine/tyramine receptor gene and was subjected to sequence analysis by multiple nucleotide and amino acid sequence alignments together with reference strain, amitraz-susceptible strain, and amitraz-resistant strain reported in other countries. LPT results suggest the absence of resistance in all of the tested populations. Interestingly, analysis of the octopamine/tyramine receptor amino acid sequence revealed four out of 14 larval pools having substitutions similar to that of the reported amitraz-resistant strains. Although no apparent resistance was observed in this study, prudent use of amitraz should be practiced as the development of resistance is still likely to occur in the future.

Acaricidal efficacy and chemical study of hexane extracts of the leaves of Neoglaziovia variegata (Bromeliaceae) against the tick Rhipicephalus microplus.

The frequent use of acaricides against the tick Rhipicephalus microplus increases the risk of development of resistance. Recent studies have revealed that Neoglaziovia variegata, an indigenous plant species known in Brazil as 'caroá', has a deleterious effect against R. microplus. In the current study, extracts of N. variegata were studied for their possible acaricidal properties. A hexane extract of N. variegata leaves was fractionated in a chromatography column and the fractions were tested in adult tick immersion tests in triplicate using three concentrations (5, 10 and 25 mg/ml). All the fractions had harmful effects on the ticks. However, three fractions were more efficaceous. Phytochemical analysis indicated that stigmast-5-en-3-ol and stigmastanol were most abundant; they might be responsible for the acaricidal effects, making them potentially useful as alternative agents to control the tick R. microplus.