Status of Rhipicephalus microplus resistance to ivermectin, fipronil and fluazuron in Mato Grosso do Sul, Brazil

Southern cattle tick resistance to pour-on and injectable acaricides has yet to be evaluated on a broader scope, and the paucity of information on the subject may hinder efforts to control this parasite. The objective of this study was to evaluate the resistance profile of ten populations of Rhipicephalus microplus to the acaricides fluazuron, fipronil and ivermectin in cattle herds in Mato Grosso do Sul, Brazil. The larval immersion test (LIT) was used to evaluate susceptibility to ivermectin and fipronil and the adult immersion test (AIT) was performed to evaluate fluazuron. Samples were randomly obtained in ten farms, and in general, we found resistance in five samples to fluazuron and in four samples to ivermectin and fipronil. Six samples showed incipient resistance to ivermectin and fipronil. Five of the ten evaluated samples showed resistance and/or incipient resistance to all the active ingredients, and the other five to two active ingredients. Among the samples classified as resistant, the average resistance ratio for ivermectin was 2.75 and 3.26 for fipronil. These results demonstrate the advanced status of resistance to the most modern chemical groups for the control of R. microplus in the state of Mato Grosso do Sul.

Biocidal potential of Eugenia pyriformis essential oil in the control of Rhipicephalus (Boophilus) microplus in the free-living cycle

ABSTRACT: Brazil has one of the largest commercial cattle herds in the world, which naturally coexist with an enormous number of parasitic species. Southern cattle tick, Rhipicephalus (Boophilus) microplus, is among these species, interfering with animal productivity and causing losses to the beef and dairy cattle sector. The use of chemical acaricides in the control of this mite has resulted in the emergence of resistant populations. In this sense, alternative control measures using plants as sources of botanical acaricides have shown to be effective. Eugenia pyriformis Cambess is a Brazilian plant with antioxidant and antimicrobial activity; however, there are no reports on its acaricidal activity in the literature. The present study aimed to evaluate the acaricidal and larvicidal potential of E. pyriformis leaf essential oil (EO) on southern cattle tick at different stages of the reproductive cycle. E. pyriformis leaves were collected and dried, and had their EO extracted by hydrodistillation (3h) using a modified Clevenger apparatus. Chemical analysis was performed by gas chromatography coupled with mass spectrometry (GC/MS), and 32 compounds belonging to the sesquiterpene class were identified: hydrocarbons (17.98%) and oxygenated forms (81.96%), with spathulenol (43.65%) and caryophyllene oxide (12.17%) as the most common. The EO was evaluated by the Adult Immersion Test at the concentrations (500.00 to 3.12mg/mL) in which the following parameters were measured: mortality of females (%), hatchability of eggs (%), and product efficiency (%). Larvae were assessed by the Larval Packet Test at concentrations ranging from 25.00 to 0.00004mg/mL. Lethal concentrations (LC) required for killing 50 and 99.9% of adult females and larvae were determined using Probit analysis. LC50 and LC99.9 of EO were 0.06 and 24.60mg/mL and 1,208.80 and 2,538mg/mL for larvae and adult females, respectively. Action of the EO in the free-living cycle of R. (B.) microplus larvae was another parameter assessed. To this end, the larvae were deposited in pots containing Brachiaria decumbens and, after migration to the leaf apex, a solution containing LC99.9 (24.60mg/mL) of the EO was sprayed. After 24h, 72.25% of the larvae had died, indicating stability of the EO when subjected to uncontrolled temperature and humidity conditions. The mechanism of action through which the EO killed the larvae and adult females was investigated by the Bioautographic Method, which showed inhibition of 3.15mg/mL of the EO on the acetylcholinesterase (AChE) enzyme. The results found in the present experiment indicate that E. pyriformis essential oil is an alternative in the control of southern cattle tick in the larval (parasitic) and free-living cycle (non-parasitic) stages under field conditions.

Baculoviral Expression of Presumptive OP-Resistance Mutations in BmAChE1 of Rhipicephalus (Boophilus) microplus (Ixodida: Ixodidae) and Biochemical Resistance to OP Inhibition

The southern cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini), transmits bovine babesiosis and anaplasmosis, and is endemic to Mexico, Latin and South America. Rhipicephalus (B.) microplus infestations within the United States are a continuing threat to U.S. cattle producers. An importation barrier between Texas and Mexico keeps the ticks from re-entering the United States. All cattle imported into the United States are dipped in an organophosphate (OP) acaricide and hand inspected for presence of ticks. Tick resistance has developed to most available acaricides, including coumaphos, the OP used in the cattle dip vats. OP-resistance can result from one or more mutations in the gene encoding the enzyme, acetylcholinesterase (AChE), resulting in production of an altered AChE resistant to OP inhibition. Previous research reported a large number of BmAChE1 mutations associated with OP resistance. We report baculovirus expression of recombinant tick BmAChE1 (rBmAChE) enzymes containing a single resistance-associated mutation, to assess their contribution to OP inhibition resistance. Surprisingly, of the naturally occurring BmAChE1 resistance-associated mutations, only D188G resulted in markedly reduced sensitivity to OP-inhibition suggesting that OP-insensitivity in BmAChE1 may result from the D188G mutation, or may possibly result from multiple mutations, each contributing a small decrease in OP sensitivity. Furthermore, an OP-insensitivity mutation (G119S) found in mosquitoes was expressed in rBmAChE1, resulting in 500-2000-fold decreased sensitivity to OP inhibition. Recombinant BmAChE1 with the G119S mutation demonstrated the lack of any structural prohibition to broad and high-level OP-insensitivity, suggesting potential increases in tick OP-resistance that would threaten the U.S. importation barrier to ticks.

Life cycle of the southern cattle tick, Rhipicephalus (Boophilus) microplus Canestrini 1888 (Acari: Ixodidae) under laboratory conditions

The southern cattle tick, Rhipicephalus (Boophilus) microplus is one of the most important tick species affecting bovine wealth worldwide. Three uninterrupted generations of this species were observed under laboratory conditions (28±3 oC and 80±5% R.H.) using rabbit hosts. The average life cycle was determined as 65±8 days. Adult feeding period averaged 7.1±1.24 days. Pre-oviposition and oviposition periods averaged 4.1±1.3 days and 8.6±0.85 days, respectively. Pre-hatching periods averaged 21.03±2.99 days. Larval free-living and feeding to moulting periods averaged 3.5±0.75 days and 7.9±0.69 days, respectively. Nymphal feeding to moulting periods averaged 10.9±1.38 days. Weights of unfed and fed females averaged 1.26±0.29 mg and 120.32±45.6 mg, respectively and produced egg masses with average weights of 29.5±9.03 mg. Number of eggs per female averaged 1455.3±434.5 eggs with peak oviposition on the 3rd day. Average hatching rate was 83.5±2.94%, and the reproduction efficiency index averaged at 12.79±2.85. The conversion efficiency index averaged at 0.26±0.05 and the reproduction fitness index averaged at 10.68±2.4. Tick recovery rate averaged at 4.7%. A strong linear relationship was found between weights of engorged females and weights of egg masses (r = 0.83) and also between weights of engorged females and number of eggs laid (r = 0.82). This work aims to describe temporal and quantitative biological facts of R. (B.) microplus life cycles. Few studies have discussed R. (B.) microplus biology in quantitative terms, and these data can be useful in designing control plans or in epidemiological studies under laboratory conditions.

Genome Sequence ofCoxiella-Like Endosymbiont Strain CLE-RmD, a Bacterial Agent in the Cattle Tick (Rhipicephalus microplus) Deutsch Strain

ABSTRACTWe report a partial genome sequence for theCoxiella-like endosymbiont strain CLE-RmD, assembled from metagenomics data obtained from the southern cattle tick (Rhipicephalus microplus) Deutsch strain.