Rhipicephalus Microplus Larvae Research Articles

Peptide-based immunoprotection against Rhipicephalus microplus tick

The main agents for tick control are chemical acaricides. However, when used without technical guidance, they can lead to environmental damage and the development of resistant tick strains. In this context, vaccines are alternative o be used in integrated tick management format by combining with other effective tools. We isolated RNA from ticks Rhipicephalus microplus, prepared the library, and performed next-generation sequencing; a pipeline analysis was applied to identify the hypothetical proteins having immunogenic potential and their predicted immunogenic peptides. Twelve peptides, ranging from 12 to 38 amino acid residues, containing the selected epitopes from different targets were selected and synthesized in two forms: the pure peptide; and the peptide conjugated to keyhole limpet hemocyanin (KLH) carrier. These peptides were divided into two groups of six peptides each. The antigen formulations (groups 1 and 2) were prepared with conjugated peptides containing 200 µg of each peptide per dose emulsified with Montanide ISA 61VG (SEPPIC); the control treatment had the adjuvant formulation without peptides (group 3). To evaluate the protective efficacy, 15 weaned male calves (Angus breed) aged around 6 months to one year and weighing approximately 200–250 kg were divided into three groups of five animals each; they were immunized thrice, at an interval of 28 days. After immunization, all the calves infested with 15,000 larvae of Rhipicephalus microplus. Peptide epitopes were recognized by antibodies against host-specific IgGs using indirect ELISA. The mean of the antibody level was determined for each group and compared using analysis of variance with two factors (ANOVA). F-test was used to determine the significance of differences observed between the groups. The percentage efficacy was calculated based on the number of ticks, the weight of teleoginas, and the weight and hatchability of the eggs, compared to that in the control group. The evaluation of immunoprotection indicated efficacies of 69 and 51 %, respectively in Group 1 and 2.

Current profile of phenotypic pyrethroid resistance in Rhipicephalus microplus (Acari: Ixodidae) populations sampled from Marathwada region of Maharashtra state, India.

This study examined the pattern of resistance to widely applied synthetic pyrethroids, i.e., cypermethrin and deltamethrin, against larvae of Rhipicephalus microplus ticks sampled from Marathwada region in Maharashtra, India. The study also examined the role of α- and β-esterases and glutathione-S-transferase (GST) in resistance development. All eight R. microplus isolates tested were resistant to deltamethrin (RL IV), having RR50 values from 6.88 to 131.26. LPT analysis exhibited the resistance level II deltamethrin resistance in Beed and Hingoli, III in Dharashiv, and IV in Sambhajinagar, Parbhani, Latur, Jalna, and Nanded isolates. The LIT analysis showed that Dharashiv field isolates had the lowest LC50 value of 229.09ppm against cypermethrin, while Sambhajinagar field isolates had the highest at 489.78ppm. The RR50 ranged from 1145.45 to 2448.9. Seven isolates were level I resistant to cypermethrin while the Jalna isolate was level II resistant. In larvae treated with deltamethrin and cypermethrin, the activity of α- and β-esterase enzymes increased significantly compared to control groups. The enzyme ratios in treated larvae ranged from 0.7533 to 1.7023 for α-esterase and 0.7434 to 3.2054 for β-esterase. The Hingoli isolate treated with cypermethrin exhibited the highest α-esterase activity (903.261), whereas Sambhajinagar isolate had the highest GST enzyme ratio (2.8224) after deltamethrin exposure. When exposed to cypermethrin, the Hingoli isolate showed the highest GST enzyme ratio, 2.0832. The present study provides the current resistance status in tick populations from Marathwada region indicating deltamethrin and cypermethrin to be ineffective for tick control. The results also suggest that SP compounds should be regulated in this region and alternative control strategies should be introduced.

Evaluation of Efficacy of Steinernema riobrave against Rhipicephalus microplus Larvae at Semi-Field Conditions

Evaluation of Efficacy of Steinernema riobrave against Rhipicephalus microplus Larvae at Semi-Field Conditions

Screening of volatile compounds of essential oils with acaricidal activity in Rhipicephalus microplus larvae using a new in vitro evaluation method

ABSTRACT The study assessed the acaricidal properties of 20 compounds derived from essential oils against the Rhipicephalus microplus tick, a significant menace to tropical livestock with considerable economic losses. A novel methodology was devised, involving the determination of mortality times for R. microplus larvae upon direct contact with these compounds. Mortality times were compared against a negative control (soybean oil) and two positive controls (commercial pour-on products). Tests were conducted in 48-well polyethylene plates, with around 100 larvae immersed in 200 µl of oil (at a 100% dose). The 10 compounds exhibiting the shortest mortality times were subsequently diluted in soybean oil at varying concentrations. Notably, thymol exhibited potent acaricidal activity, with the lowest effective dose (1.56%) resulting in larval mortality within 15 minutes, whereas positive controls necessitated over 66 minutes. A correlation was established between the molecular structure of the compounds and their acaricidal efficacy, indicating that cyclic compounds containing 10 carbon atoms demonstrated heightened lethality compared to acyclic counterparts. This innovative methodology enables the rapid identification of substances with substantial acaricidal potential in vitro, yielding results within minutes, in stark contrast to the traditional larval immersion test, which demands a minimum of 24 hours for conclusive outcomes.

The potential effect of Garlium GEM HCTM as a tick control agent in cattle.

As resistance to chemical acaricides increases amongst tick populations, investigations of natural remedies that have acaricidal or tick-repellent effects have become essential in the search for alternatives for sustainable tick control. Garlium GEM HC (Garlium), a natural concentrated garlic product, was supplemented in-feed to beef cattle to determine if it could assist in reducing the number of attached ticks on cattle. Two grams of Garlium was supplemented daily to eight Bonsmara steers over 43 days. A second group of eight steers served as controls. All animals were infested with a similar number of Rhipicephalus appendiculatus adults and Rhipicephalus microplus larvae. Subsequently, the number of attached engorged ticks and the hatchability of the tick eggs were determined. Blood samples were collected from the steers for whole blood analyses. The results were analysed using a twosample t-test procedure. Due to large standard deviations observed, most of the tick parameters were only numerically improved. Although not significant, the number of larvae produced by female R. appendiculatus ticks per host was reduced by 23%. Estimated number of R. microplus larvae produced from ticks harvested from Garlium supplemented cattle were reduced by 42.3% (p = 0.10). No adverse effect was observed on haematocrits or haemoglobin concentrations. Garlium reduced segmented neutrophil count in the treatment group, suggesting that the immune system was less challenged. Although not statistically significant, the effect of reducing the number of larvae produced per host for the two tick species by approximately 20% and 40% respectively, may be of economic benefit to commercial cattle farmers.

First report of acaricidal efficacy from plumbagin on larvae of Rhipicephalus microplus and Rhipicephalus sanguineus resistant to conventional acaricides

The problem of resistance to acaricides in ticks such as Rhipicephalus microplus and R. sanguineus has motivated the search for control alternatives, such as the use of extracts and secondary metabolites from plants. Plumbagin is a natural product present in plants such as Plumbago zeylanica L., Diospyros kaki, and D. anisandra, of which acaricidal activity has been reported. Therefore, the objective of this study was to evaluate in vitro the acaricidal efficacy of plumbagin on larvae of R. microplus and R. sanguineus resistant to conventional acaricides. Larvae from engorged female ticks, collected from naturally infested dairy cattle and domiciled dogs, in Yucatan, Mexico, were used. The larval packet test and the larval immersion test were performed to detect acaricide susceptibility. Both tick populations were detected as resistant to cypermethrin and amitraz. Then, the modified larval immersion test was used and plumbagin was evaluated at concentrations of 1%, 0.5%, 0.25%, and 0.125% (%w/v), obtaining a mortality of 100% in the four concentrations for both tick species. Subsequently, lower doses of plumbagin were evaluated at concentrations of 0.0625%, 0.03125%, 0.015625% and 0.0078125%, obtaining mortalities of 100 to 36.26% for R. microplus and 100%–5.33% for R. sanguineus. Using Probit analysis, lethal concentrations at 50% (LC50), 99% (LC99) and confidence intervals at 95% (CI95%) were calculated. R. microplus showed a LC50 of 0.011% (CI95%: 0.010–0.011) and LC99 of 0.019% (CI95%: 0.018–0.022). R. sanguineus presented a LC50 of 0.017% (CI95%: 0.015–0.018) and CL99 of 0.031% (CI95%: 0.027–0.036). It was concluded that plumbagin has high acaricidal efficacy against larvae of R. microplus and R. sanguineus resistant to amitraz and cypermethrin. R. microplus larvae were significantly more susceptible to LC50 and LC99 compared to R. sanguineus. This is the first report on the acaricidal efficacy of plumbagin on larvae of R. microplus and R. sanguineus resistant to conventional acaricides.

Vaccination of cattle with the Babesia bovis sexual-stage protein HAP2 abrogates parasite transmission by Rhipicephalus microplus ticks

The apicomplexan parasite Babesia bovis is responsible for bovine babesiosis, a poorly controlled tick-borne disease of global impact. The widely conserved gametocyte protein HAPLESS2/GCS1 (HAP2) is uniquely expressed on the surface of B. bovis sexual stage parasites and is a candidate for transmission-blocking vaccines (TBV). Here, we tested whether vaccination of calves with recombinant HAP2 (rHAP2) interferes with the transmission of B. bovis by competent ticks. Calves vaccinated with rHAP2 (n = 3), but not control animals (n = 3) developed antibodies specific to the vaccine antigen. Vaccinated and control animals were infested with Rhipicephalus microplus larvae and subsequently infected with virulent blood stage B. bovis parasites by needle inoculation, with all animals developing clinical signs of acute babesiosis. Engorged female ticks fed on the infected calves were collected for oviposition, hatching, and obtention of larvae. Transmission feeding was then conducted using pools of larvae derived from ticks fed on rHAP2-vaccinated or control calves. Recipient calves (n = 3) exposed to larvae derived from control animals, but none of the recipient calves (n = 3) challenged with larvae from ticks fed on rHAP2-vaccinated animals, developed signs of acute babesiosis within 11 days after tick infestation. Antibodies against B. bovis antigens and parasite DNA were found in all control recipient animals, but not in any of the calves exposed to larvae derived from HAP2-vaccinated animals, consistent with the absence of B. bovis infection via tick transmission. Overall, our results are consistent with the abrogation of parasite tick transmission in rHAP2-vaccinated calves, confirming this antigen as a prime TBV candidate against B. bovis.

Evaluation of Acaricidal Activity of Cinnamomum camphora (F. Lauraceae) Essential Oil Nanoemulsion Against Cattle Tick Rhipicephalus microplus

The present study aims at preparing nanoemulsions of plant essential oil Cinnamomum camphora as acaricidal agent against cattle tick Rhipicephalus microplus larvae. In the initial step, the phytochemical screening of oil was done through gas chromatography and mass spectrometry depicting major compounds as α-pinene (53.99%) and camphor (20.89%) in C. camphora oil. Different ratios of Cinnamomum camphora oil and surfactant Tween 80 (oil:surfactant- 1:0.25, 1:0.5, 1:1, 1:1.5, 1:2 and 1:2.5) were used for preparing stable nanoemulsion through ultrasonication approach. Thermodynamic stability analysis exhibited that CA3 ratio (1:1) to be the most stable which was further characterized using Dynamic light scattering study through Nano zeta sizer indicating droplet size of 101.60 nm, polydispersity index as 0.50 and zeta potential value measured as -8.59 mV. Spectral analysis through Fourier Transform Infrared spectrometry for functional group interaction and Transmission electron microscopy for morphology of nanoemulsion droplets was also done for CA3 nanoemulsion. Acaricidal activity of stable nanoemulsion was evaluated against R. microplus larvae using larval packet assay and repellency rod test with concentration ranging from 500 ppm to 20000 ppm and 500 ppm to 25000 ppm respectively. Highest concentration (20000 ppm) showed 77% mean mortality with LC₅₀ (3364.46 ppm) after 24 hour. CA3 showed promising repellent activity that ranged from 27% to 87% at various concentrations at different time intervals. These findings proved that Cinnamomum camphor essential oil nanoemulsion could be developed and used against R. microplus larvae as a safer, greener and nanoacaricide product.

Potential of Tetradenia riparia leaf essential oil and its fractions in controlling Aedes aegypti and Rhipicephalus microplus larvae

Tetradenia riparia (Hochst.) Codd (Lamiaceae) is a shrub, commonly known as ginger bush or false myrrh, and several studies have shown that T. riparia exhibits a variety of biological properties. This study aimed to determine the chemical composition of T. riparia essential oil and its fractions, investigate their anticholinesterase activity, and assess their larvicidal activity against the cattle tick Rhipicephalus microplus and the mosquito Aedes aegypti. Eleven essential oil fractions were obtained by fractionation and analyzed by gas chromatography/mass spectrometry. Larvicidal activity against R. microplus and third-instar A. aegypti was assessed using a larval packet test and a larval immersion test, respectively. Anticholinesterase activity was determined by a bioautographic method. Forty-nine compounds were identified in the essential oil, of which the major classes were oxygenated sesquiterpenes (45.95%) and sesquiterpene hydrocarbons (35.20%) and the major components were isospathulenol (17.40%), β-caryophyllene (15.61%), 14-hydroxy-9-epi-caryophyllene (10.07%), 14-hydroxy-α-muurolene (8.32%), and 9β,13β-epoxy-7-abietene (5.53%). Bioassays showed that T. riparia essential oil (LC50 = 1.56 µg/mL) and FR3 (LC50 = 0.30 µg/mL) were the most active against R. microplus and A. aegypti larvae, respectively. The essential oil and FR1, FR2, and FR3 exhibited acetylcholinesterase inhibitory activity. These results indicate that T. riparia essential oil and its fractions hold promise in the development of novel, environmentally safe agents for the control of R. microplus and A. aegypti larvae.

Seasonal and Circadian Evaluation of the Pectis brevipedunculata Essential Oil and Its Acaricidal Activity against Rhipicephalus microplus (Acari: Ixodidae)

Pectis brevipedunculata is native species and widely available in dry and semi-arid ecosystems showing high biotechnological potential. The objective of this study was to evaluate the circadian and seasonal chemical variation of the essential oil (EO) of P. brevipedunculata, as well as its acaricide effect on Rhipicephalus microplus larvae. Aerial parts were collected and submitted to the hydrodistillation process, and the chemical composition was determined by gas chromatography mass spectrometry (GC-MS). For the assays with R. microplus, the larval immersion test was performed. The main constituents were citral (75% of the EO), followed by α-pinene and limonene. In the seasonality analysis, the highest yields were in the months of April (2.08%) and August (2.05%), while in the study of circadian rhythm, the percentage was 2.0% at 6 p.m. in the rainy season, and 1.2%, dry season at 6 p.m. Concerning acaricidal activity (50% lethal concentration (LC50)), the April (1.17 mg mL-1), March (1.28 mg mL-1), June (1.37 mg mL-1), and October (1.27 mg mL-1) oils obtained were the most active and assays performed with circadian rhythm revealed in the rain season (April) at 6 p.m. and dry season (September) at 12 a.m. LC50 values of 1.75 and 1.75 mg mL-1, respectively. Additionally, this EO is selective to non-target organisms, i.e., ladybeetles and lacewing.

Evaluation of the susceptibility to fipronil of Rhipicephalus microplus larvae from egg masses incubated at different times of oviposition.

The objective of this work was to evaluate the susceptibility of R. microplus larvae from different oviposition times to fipronil. The LPT was performed in sextuplicate, at concentrations of 18.75, 37.5, 75, 150 and 300 µg.mL-1. The LC50 found for the egg masses incubated with +7, +14 and +21 days were respectively 105.87, 110.71 and 121.22 µg.mL-1. The larvae originating from egg masses from the same group of engorged females, incubated on different days, presented similar mortality rates compared to the evaluated fipronil concentrations, facilitating the maintenance of laboratory colonies of this tick species.

Allium sativum extract against free-living larvae of Rhipicephalus microplus: a potential environmental biocontrol.

The infestation of Rhipicephalus microplus (Acari: Ixodidae) (Canestrini, 1887) represents a significant health problem for cattle. Up until today, no consistent control has been recommended for the free-living larval stage of R. microplus. The objective of the present study was to determine the larvicidal effect of an Allium sativum (garlic) aqueous extract against R. microplus using the larval package test, LPT. Tick larvae were obtained from adult female ticks from naturally infected animals, and 200 larvae were exposed to each A. sativum extract concentration (5, 7, 10, 16, 25, and 50%). All garlic groups received the extract in three different volumes (2, 5, and 7ml) to determine the levels of humidity that would affect the free-living stage. Larvae from the control group were treated with distilled water and the positive control used cypermethrin in a 5-ml volume. Live and dead larvae were determined after 24h of exposure. There was a significant statistical difference (P=0.041) at 5% between 2 and 5ml and between 7 and 10% of the extract using 2ml (P=0.034). There was a significant larvicidal activity of 100% mortality for the 16, 25, and 50% concentrations for all volumes. We observed a clear concentration-dependent effect for the extracts with a correlation coefficient of R2>0.92. The lethal concentration of 50% (LC50) was 13.6, 9.8, and 7.6% for the 2, 5, and 7ml. The present A. sativum solutions may be considered a viable biofriendly alternative to reduce the number of the free-living larval stage of R. microplus on pasture and the consequent reduction of cattle infestation due to its high larval mortality.

Coxiella Endosymbiont of Rhipicephalus microplus Modulates Tick Physiology With a Major Impact in Blood Feeding Capacity.

In the past decade, metagenomics studies exploring tick microbiota have revealed widespread interactions between bacteria and arthropods, including symbiotic interactions. Functional studies showed that obligate endosymbionts contribute to tick biology, affecting reproductive fitness and molting. Understanding the molecular basis of the interaction between ticks and their mutualist endosymbionts may help to develop control methods based on microbiome manipulation. Previously, we showed that Rhipicephalus microplus larvae with reduced levels of Coxiella endosymbiont of R. microplus (CERM) were arrested at the metanymph life stage (partially engorged nymph) and did not molt into adults. In this study, we performed a transcriptomic differential analysis of the R. microplus metanymph in the presence and absence of its mutualist endosymbiont. The lack of CERM resulted in an altered expression profile of transcripts from several functional categories. Gene products such as DA-P36, protease inhibitors, metalloproteases, and evasins, which are involved in blood feeding capacity, were underexpressed in CERM-free metanymphs. Disregulation in genes related to extracellular matrix remodeling was also observed in the absence of the symbiont. Taken together, the observed alterations in gene expression may explain the blockage of development at the metanymph stage and reveal a novel physiological aspect of the symbiont-tick-vertebrate host interaction.

Acaricidal activity of the essential oil from Senecio cannabifolius and its constituents eucalyptol and camphor on engorged females and larvae of Rhipicephalus microplus (Acari: Ixodidae).

The objective of this experiment was to evaluate the acaricidal activity of Senecio cannabifolius essential oil, and two of its constituents, eucalyptol and camphor. Efficacy against females and larvae of Rhipicephalus (Boophilus) microplus was assessed by the adult immersion test (AIT) and the larval immersion test (LIT). The oil was analyzed by gas chromatography-flame ionization detection (GC-FID) and GC-mass spectrometry (MS) and in total 68 components were identified representing 99.2% of the essential oil. AIT revealed that the oil, eucalyptol, and camphor at the highest concentration presented efficacy of 68.9, 57.1, and 71.9%, respectively. LIT revealed that the essential oil and camphor achieved 100% mortality at concentration of 1.6% wt/vol, whereas eucalyptol showed moderate inhibitory activity. Biochemical assays indicated that the essential oil and camphor can reduce significantly overall detoxification enzyme activities in engorged females and larvae at high concentration (≥ 0.4% wt/vol), whereas the inhibitory effect of eucalyptol is weaker than that of the oil and camphor. Taken together our results indicated that the S. cannabifolius essential oil and its isolated constituent had potential for the development of a new and safe acaricide for the control of R. microplus ticks.

In Vitro Effect of Volatile Substances from Eucalyptus Oils on Rhipicephalus microplus

Volatile oils have been extensively investigated as an alternative for tick control. This study evaluated the in vitro effects of volatile compounds emanated by Corymbia citriodora (Hook.) K.D.Hill & L.A.S.Johnson and Eucalyptus globulus Labill., Myrtaceae, volatile oils and their major compounds, citronellal and 1,8-cineole, respectively, at doses of 10, 20, 40, 60, 80 and 100 mg/g, on Rhipicephalus microplus larvae and engorged females. The effects of these volatile oils were compared with those of commercial acaricides. In bioassays with engorged females, percentages of oviposition inhibition (OI %) and efficacy of the product (EP %) were determined, as well as tick larval mortality. The larval tests with citronellal presented high mortalities (> 80%) for all analysed doses, except 10 mg/g, while those for 1,8-cineole at the lowest dose (10 and 20 mg/g) produced the highest mortality (> 85%). In general, the volatile compounds released by these oils resulted in larval mortality and inhibition of the reproductive parameters in the engorged females, with efficacies over 80%.

Repellency effect of Pilocarpus spicatus A. St.-Hil essential oil and nanoemulsion against Rhipicephalus microplus larvae

Rhipicephalus microplus, the cattle tick, is a major cause of economic losses in bovine production. Due to the widespread acaricidal resistance to commercially available products, as well as their toxicity and environmental impact, alternative control methods are required. Nanoformulations produced from plant extracts as bioactive substances are very promising as innovative acaricidal agents. Thus, the aim of this study was to evaluate the in vitro repellent activity of Pilocarpus spicatus essential oil and its nanoemulsion against R. microplus, using larval repellent test (RT). The essential oil was extracted by hydrodistillation, using a Clevenger-type apparatus. The nanoemulsion was prepared with 5% essential oil, 5% tween 80, and 90% water, using the phase inversion method (50 mg/mL). Limonene was the major component (46.8%) of the essential oil, as determined by gas chromatography-mass spectrometry (GC/MS) and confirmed by flame ionization detection (GC/FID). According to the RT results, the essential oil had a repellent activity greater than 69%, from concentrations of 3.12 mg/mL (69.81 ± 10%) to 50 mg/mL (98.10 ± 0.6%), whereas the nanoemulsion at 50 mg/mL presented repellent activities of 97.14 ± 1.37% and 97.89 ± 0.52% 6 and 10 h after treatment, respectively. These values regarding to total repellency were very close to those calculated for mortality corrected by Abbott's formula. The phase inversion method preserved the chemical and physical characteristics of the essential oil since both reached an equal repellent effect at the same concentration. Therefore, P. spicatus essential oil and nanoemulsion had excellent repellent activities against R. microplus larvae, demonstrating its potential for future use as an alternative for tick control.

Activation of the ambusher tick Rhipicephalus microplus (Acari: Ixodidae) exposed to different stimuli.

The present study aimed to evaluate the behaviour of larvae of Rhipicephalus microplus exposed to different stimuli. A Y-olfactometer was positioned vertically and R. microplus larvae were exposed to environmental air, CO2 alone, N,N-diethyl-3-methylbenzamide (DEET) alone, and CO2 combined with the repellents DEET and (E)-2-octenal. Tests were also conducted with the olfactometer positioned horizontally; in this case, however, only CO2 was tested. In all tests conducted with the Y-olfactometer positioned vertically, CO2 activated R. microplus larvae even in the presence of DEET and (E)-2-octenal, although activation was lower when these repellents were used. In the absence of CO2 , larval behaviour against DEET was similar to that of the larvae in the control group. In the tests performed with the olfactometer positioned horizontally, the larvae had no significant response to the presence of CO2 . The larvae were not attracted to or repelled by any compound tested in either the vertical or horizontal position of the olfactometer. The lack of horizontal displacement, attraction or repellence may have been a result of the ambush behaviour of this tick species. However, when larvae were exposed to stimuli and the olfactometer was positioned vertically, the interference of attractant and repellent stimuli in larval behaviour was assessed.

Effect of entomopathogenic native fungi from paddock soils against Rhipicephalus microplus larvae with different toxicological behaviors to acaricides

The objectives of this study are to: (1) evaluate the in vitro acaricidal effect of 54 Metarhizium anisopliae strains, six Beauveria bassiana strains and one Purpureocilium lilacinum strain, against the larvae of two populations of Rhipicephalus microplus (multi-resistant and susceptible to chemical acaricides); and (2) determine the lethal concentrations required to eliminate the 50% (LC50) and 99% (LC99) of larvae through the use of entomopathogenic fungi (EF) with high acaricidal effects. The mortality percentage was evaluated by larval immersion tests at a dose of 1 × 108 conidia/mL for each fungal strain. For calculating LC50 and LC99, four doses (1 × 108, 1 × 107, 1 × 106 and 1 × 105) were used. Nine strains of M. anisopliae and the P. lilacinum strain showed a high mortality percentage in the R. microplus larvae of both populations. The best strains that showed the lowest values of LC50 and LC99 for tick elimination were MaV50 and PlV01. In conclusion, several strains of entomopathogenic fungi showed a high acaricidal effect against the R. microplus larvae of both populations, suggesting that these fungi might be a promissory adjuvant in the control of R. microplus, including those who are resistant. Finally, the discovery of a P. lilacinum strain with a high acaricidal effect is also reported.

Resistance to the tick Rhipicephalus microplus and Babesia bovis infection levels in beef heifers raised in an endemic area of Sao Paulo state, Brazil

Repeatability coefficients (r) for tick resistance and Babesia bovis infection levels and the correlation (ρ) between these traits were estimated in beef heifers, using artificial infestations and short intervals between measurements. Forty heifers, including 20 Bos taurus taurus (Caracu) and 20 Bos taurus indicus (Nelore) animals, were submitted to three artificial infestations with Rhipicephalus microplus larvae at intervals of 14 days. The number of standard female was counted from the 19th through the 23rd day after each infestation, considering only the left side of each animal. Blood samples were collected on Days 0, 6, 20, 34 and 48 after the first infestation. The number of copies of B. bovis DNA (CN) was estimated from blood samples through the quantitative PCR technique to evaluate the level of infection in the animals. Total tick count (TTC), the percentage of return (PRij) and CN were analysed using the MIXED procedure of the SAS program. The r of the variables were estimated by intraclass correlation between measures of the same animal, with the variance component of the animal being divided by the phenotypic variance (residual + animal), using models with a CS structure matrix. Additionally, ρ among variables were estimated using the CORR procedure. The following results were obtained for Caracu and Nelore animals, respectively: 1.83 ± 0.37 and 0.63 ± 0.40 for TTC, 1.10 ± 0.23 and 0.47 ± 0.23 for PRij, and 2.29 ± 0.64 and 2.32 ± 0.58 for CN. The r was moderate for TTC (0.62) and PRij (0.53) and low for CN (0.10). The ρ between TTC and CN obtained in the same measurement day was not significant in either breed (P > 0.05; –0.07 for Caracu and 0.19 for Nelore). Results showed both breeds were able to develop resistance against B. bovis; however, Nelore exhibited higher tick resistance. The r obtained for CN and the weak association with tick resistance indicate that it is not possible to recommend the use of CN as a trait to predict tick resistance in these two breeds.

QPCR estimates of Babesia bovis and Babesia bigemina infection levels in beef cattle and Rhipicephalus microplus larvae.

Babesia spp. are tick-transmitted intraerythrocytic apicomplexan parasites that infect wild and domestic animals. Babesia bovis and B. bigemina are endemic and responsible for enormous economic losses to the livestock industry in most of the Brazilian territory, wherein the tick Rhipicephalus microplus is the unique vector. Better understanding of epidemiology and parasite-host interactions may improve the tools for disease control and genetic management for selection of resistant animals. This study aimed to detect, quantify and measure the correlation between B. bigemina and B. bovis infection levels in bovine blood and into tick, by absolute quantification of hemoparasite DNA using qPCR. Blood bovine samples and larvae pools from 10 engorged R. microplus females were collected from each Canchim heifers (5/8 Charolais + 3/8 zebu, n = 36). All evaluated samples were positive for both Babesia species tested. Correlations of B. bovis and B. bigemina levels between cattle and tick host were 0.58 and 0.66, respectively. These high positive correlation coefficients indicate that parasitemia load in the bovine may be dependent on or may determine the parasitemia load in the ticks.