Larval Packet Test Research Articles

In vitro and in vivo evaluation of cypermethrin, amitraz, and piperonyl butoxide mixtures for the control of resistant Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) in the Mexican tropics

A study was conducted to evaluate the efficacy of cypermethrin, amitraz, and piperonyl butoxide (PBO) mixtures, through in vitro laboratory bioassays and in vivo on-animal efficacy trials, for the control of resistant Rhipicephalus (Boophilus) microplus on cattle in the Mexican tropics. Also, to examine mechanisms of resistance to cypermethrin in this tick population, the frequency of a mutated sodium channel gene (F1550I) was determined using a PCR assay. Results of laboratory bioassays using modified larval packet tests revealed that cypermethrin toxicity was synergized by PBO (from 46.6–57.0% to 83.7–85.0% larval mortality; P<0.05). The cypermethrin and amitraz mixture showed an additive effect (from 46.6–57.0% to 56.0–74.3% larval mortality). Strong synergism was observed with the mixture of cypermethrin+amitraz+PBO and this mixture was the most effective killing resistant tick larvae in vitro (96.7–100% of larval mortality). Tick larvae surviving exposure to cypermethrin or mixtures either with amitraz and PBO in vitro showed 2.9–49.6 higher probability to present the mutated allele than those killed by acaricide treatment (P<0.05). In the in vivo trial, the mixtures containing cypermethrin+PBO (80.6–97.3%), and cypermethrin+amitraz (87.0–89.7%) were more efficacious than cypermethrin alone (76.3–80.5%). The highest level of efficacy was obtained with the mixture of cypermethrin+amitraz+PBO, which yielded >95% control that persisted for 28 days post-treatment against R. microplus infesting cattle when tested under field conditions in the Mexican tropics. Although this mixture is a potentially useful tool to combat pyrethroid resistance, a product based on an acaricide mixture like the one tested in this study has to be used rationally.

Investigation of activity of monoterpenes and phenylpropanoids against immature stages of Amblyomma cajennense and Rhipicephalus sanguineus (Acari: Ixodidae)

The objective of this study was to assess the acaricidal activity of carvacrol, thymol, eugenol, and (E)-cinnamaldehyde on unengorged larvae and nymphs of Amblyomma cajennense and Rhipicephalus sanguineus, using the modified larval packet test. Carvacrol, eugenol, and (E)-cinnamaldehyde were tested at concentrations of 2.5, 5.0, 10.0, 15.0, and 20.0 μl/ml, while thymol was tested at concentrations of 2.5, 5.0, 10.0, 15.0, and 20.0 mg/ml, in all cases with 10 repetitions per treatment. For the A. cajennense larvae, mortality rates caused by carvacrol, thymol, eugenol, and (E)-cinnamaldehyde at the lowest concentration were 45.0, 62.7, 10.2, and 81.6%, respectively, reached 100% at the concentration of 5.0 μl/ml for carvacrol and (E)-cinnamaldehyde and 5.0 mg/ml for thymol, while this mortality was observed at 15.0 μl/ml for eugenol. For the nymphs of this species, carvacrol and thymol caused 100% mortality starting at a concentration of 5.0 μl/ml and 10.0 mg/ml, respectively, while eugenol caused 100% mortality at 20.0 μl/ml and the mortality caused by (E)-cinnamaldehyde did not exceed 64%. In the tests with R. sanguineus larvae, the lowest concentration of carvacrol and (E)-cinnamaldehyde resulted in 100% mortality, while this percentage was observed starting at 10.0 μl/ml for eugenol. For nymphs, carvacrol and thymol at the smallest concentration caused 100% lethality, unlike the results for eugenol and (E)-cinnamaldehyde, where 100% mortality was only observed starting at the concentration of 10.0 μl/ml. The results obtained indicate that the tested substances have acaricidal activity on unengorged larvae and nymphs of A. cajennense and R. sanguineus.

In vitro assessment of the acaricidal activity of computer-selected analogues of carvacrol and salicylic acid on Rhipicephalus (Boophilus) microplus

Rhipicephalus (Boophilus) microplus is a tick that causes huge economic losses in cattle. The indiscriminate use of acaricides has generated resistance to most compounds present on the market. This makes further investigation on other potential acaricides necessary, the in silico assay being an alternative to the design of new compounds. In the present study a biosilico assay was performed using TOMOCOMD-CARDD (TOpological MOlecular COMputer Design-Computer-Aided Rational Drug Design) and WEKA (Waikato Environment for Knowledge Analysis) software. Two carvacrol and four salicylic acid derivatives, synthesized by conventional methods and evaluated with the larval packet test on larvae of R. (B.) microplus were selected. All evaluated compounds presented acaricidal activity; however, ethyl 2-methoxybenzoate (91.8 ± 1.7 % mortality) and ethyl 2,5-dihydroxybenzoate (89.1 ± 1.6 % mortality) showed greater activity than salicylic acid. With regard to the carvacrol analogues, carvacrol acetate (67.8 ± 2.1 % mortality) and carvacrol methyl ether (71.7 ± 1.6 % mortality) also showed greater activity than carvacrol (35.9 ± 3.2 % mortality). TOMOCOMD-CARDD and WEKA software were helpful tools in the search for alternative structures with potential acaricidal activity on R. (B.) microplus.

&amp;lt;i&amp;gt;In Vitro&amp;lt;/i&amp;gt; and &amp;lt;i&amp;gt;in Vivo&amp;lt;/i&amp;gt; Efficacy of an Experimental Compound against &amp;lt;i&amp;gt;Rhipicephalus (Boophilus) microplus&amp;lt;/i&amp;gt; Ticks

The aim of the present study was to evaluate the ixodicide efficacy of the experimental compound 712-BF-016 against Rhipicephalus (Boophilus) microplus ticks in vitro and in cattle. The in vitro efficacy was initially tested against R. Boophilus microplus larvae using the Larval Packet Test (LPT). In a 2nd study the ixodicide efficacy was tested against adult ticks using the Adult Inmersion Test (AIT). Finally, a field test with the compound was carried out using 24 steers experimentally infested with R. (Boophilus) microplus ticks which were divided into 4 groups of 6 animals each for treatment. Groups 1 and 2 received the experimental compound at concentrations of 16% and 20%, respectively, which were applied as an aspersion in a total volume of 4 liters/animal. Group 3 was equally treated but with a commercial ixodicide containing cipermethrin at a 16% concentration. Group 4 served as untreated control. The efficacy was measured on days 1, 2, 3 after treatment as the percentage of ticks present from the treated groups, relative to the ticks present in the untreated control. The results indicated a percentage mortality of 93.21% for LPT and 98.02% for AIT. The efficacy produced in cattle was 61.78%, 76.43% and 85.34% for groups 1, 2 y 3, respectively. It is concluded that there was no concordance between the results obtained in vitro with those found in cattle. Possibly the excipient used for the formulation of the experimental compound was not suitable and had some influence on the results.

Effect of new ethyl and methyl carbamates on biological parameters and reproduction of the cattle tick Rhipicephalus microplus

The effect of carbamates on engorged female Rhipicephalus microplus ticks and larvae was evaluated using the adult immersion test (AIT) and the larval packet test (LPT), respectively. Seventeen synthetic carbamates different from current commercial acaricides were synthesised at the National Autonomous University of Mexico. None of the carbamates had an effect on the percentage of females laying eggs. Six of the compounds inhibited egg laying up to 65.4% and inhibited egg hatching by up to 100% (p<0.05). Compared to untreated females, eggs produced by treated females had a dark, dry, opaque appearance and were less adherent. Carbamates LQM 934 and LQM 938 had an effect on larval mortality (p<0.05). Carbamate LQM 934 showed lethal concentrations (LC) of LC90=0.76% and LC99=0.87%, while LQM 938 showed concentrations of LC90=0.267% and LC99=0.305%. The compounds were distributed into three classes of acaricidal activity using the AIT or the LPT. These three classes were as follows: (1) compounds having no apparent effect; (2) compounds that inhibit egg laying and embryo development or (3) compounds that exhibit acaricidal activity to larval ticks.

Activity of essential oil of Lippia triplinervis Gardner (Verbenaceae) on Rhipicephalus microplus (Acari: Ixodidae)

The objective of this work was to characterize and investigate the acaricidal activity of the essential oil of the aerial parts of Lippia triplinervis at different concentrations on unengorged larvae and engorged females of Rhipicephalus microplus. The essential oil yielded 2.21 % (w/w to dry matter) and was composed mainly of carvacrol (31.9 %), thymol (30.6 %), and p-cymene (12.3 %). Two tests were performed to assess the acaricidal activity: the modified larval packet test, with concentrations of 2.5, 5.0, 10.0, 15.0, and 20.0 mg/mL and the female immersion test, with concentrations of 10.0, 20.0, 30.0, 40.0, and 50.0 mg/mL. There were ten repetitions for each concentration, and for each test, a control group was formed in which the ticks were treated with Tween 80 (20 mg/mL). The experimental groups were kept in a climate-controlled chamber (27 ± 1 °C and RH >80 %). The mortality of the larvae was above 95 % in all the groups tested and reached 100 % as of the 5.0 mg/mL concentration, while the control group exhibited 0 % mortality. In the female immersion test, there was a significant decline (p < 0.05) in the egg mass weight, egg production index, and hatching percentage starting at the concentration of 30.0, 40.0, and 20.0 mg/mL, respectively, and the control percentage at the concentrations of 40.0 and 50.0 mg/mL were above 90 and 95 %. The L. triplinervis oil as thus an alternative source of the monoterpenes thymol, carvacrol, and p-cymene, and its toxicity on R. microplus larvae and females makes it promising possibility for control of this tick.

Chemical identification of Tagetes minuta Linnaeus (Asteraceae) essential oil and its acaricidal effect on ticks

The control of tick species that affect animal production is vital for the economic welfare of the cattle industry. This study focused on testing the acaricidal activity of the essential oil from the leaves and stems of Tagetes minuta against several Brazilian tick species, including Rhipicephalus (Boophilus) microplus, Rhipicephalus sanguineus, Amblyomma cajennense and Argas miniatus. The chemical composition of the essential oil was determined by chromatography and spectroscopy analyses, which revealed the presence of monoterpenes. The adult immersion test (AIT) and the larval packet test (LPT) were used to evaluate the efficacy of T. minuta essential oil in tick management at concentrations of 2.5, 5, 10, 20 and 40%. The results demonstrated that the T. minuta essential oil had over 95% efficacy against four species of ticks at a concentration of 20%. These results suggest that the essential oil of T. minuta could be used as an environmentally friendly acaricide.

Chemical composition and acaricidal activity of essential oil from Lippia sidoides on larvae of Dermacentor nitens (Acari: Ixodidae) and larvae and engorged females of Rhipicephalus microplus (Acari: Ixodidae)

The aim of this work was to identify the compounds and to investigate the acaricidal activity of the essential oil from the leaves of Lippia sidoides on Rhipicephalus microplus and Dermacentor nitens. The oil was obtained by hydrodistillation and analyzed by gas chromatography (GC/FID) and gas chromatography/mass spectrometry. In total, 15 compounds comprising 99.97 % of the total peak area were identified. The main constituent of the essential oil was thymol (67.60 %). The acaricidal activity was assessed by the modified larval packet test, with oil concentrations of 2.5, 5.0, 10.0, 15.0, and 20.0 μl/ml, and by the female immersion test with concentrations of 10.0, 20.0, 40.0, 60.0, and 80.0 μl/ml. The mortality of the R. microplus and D. nitens larvae was greater than 95 % starting at concentrations of 10.0 and 20.0 μl/ml, respectively. In the test with the engorged females, the L. sidoides essential oil starting at a concentration of 40.0 μl/ml caused a significant reduction (p < 0.05) in the values of the egg mass weight and egg production index. The viability of the eggs was affected in all the treated groups, with significantly lower hatching rates (p < 0.05) in relation to the control group. The control percentages at concentrations of 10.0, 20.0, and 30.0 μl/ml were 54, 57, and 72 %, and reached 100 % at the highest two concentrations (60.0 and 80.0 μl/ml). Therefore, it can be concluded that the essential oil from the leaves of L. sidoides has acaricidal activity on R. microplus and D. nitens.

Use of the Larval Tarsal Test to determine acaricide resistance in Rhipicephalus (Boophilus) microplus Brazilian field populations

Acaricide resistance of the cattle tick Rhipicephalus (Boophilus) microplus is widespread in most of the countries where this parasite is present. Bioassays are used to diagnose the level and pattern of resistance in tick populations. In the present study, we describe a detailed protocol of the Larval Tarsal Test (LTT) using simplified equipment and data on the resistance of 17 tick field populations originating from 5 Brazilian states. Nine acaricidal compounds from 5 major classes were tested: organophosphates (OP), synthetic pyrethroids (SP), macrocyclic lactones (ML), phenylpyrazols (PYZ) and amidines. For comparison, four of the tick populations were also tested with the Larval Packet Test (LPT) with one compound per class. The most common resistances were to SP, amitraz and OP, with frequencies of 94%, 88% and 82%, respectively. Resistance to PYZ was also found to be widespread (65%), suggesting a rapid development of fipronil resistance in Brazil. One case of ML resistance and 2 cases of suspected ML resistance were identified with the LTT. The LTT led to higher resistance ratios to all compounds than the LPT, reflecting its high sensitivity to detect resistance. Finally, the LTT allowed testing a larger number of compounds and doses with reduced labour in comparison to the LPT and turned out to be a reliable bioassay to detect resistance in field populations.

Tick control practices in Burkina Faso and acaricide resistance survey in Rhipicephalus (Boophilus) geigyi (Acari: Ixodidae)

Traditional systems account for 95% of the livestock produced in Burkina Faso. Tick infestation hampers livestock productivity in this area. However, little information exists on tick-control practices used by livestock farmers. We interviewed 60 stockbreeders working in traditional farming systems to obtain the first data on tick-control practices. Sixteen farmers (27%) did not use conventional practices: seven removed ticks by hand or plastered cattle with dung or engine oil; nine farmers treated cattle with crop pesticides. Forty-four farmers (73%) used mainly synthetic pyrethroids (SP; either alphacypermethrin or deltamethrin in 20 and 18 farms, respectively) and occasionally amitraz (N=6). Intervals between treatments varied significantly depending on the chemical used: most farmers using crop pesticides (100%), amitraz (100%) or alphacypermethrin (80%) adjusted tick-control to tick-burden, whereas farmers using deltamethrin tended more to follow a tick-control schedule. Perception of tick-control effectiveness significantly varied among practices: tick-control failures were more frequently reported by farmers using alphacypermethrin (55%) than by those using either other conventional acaricides (17%) or crop pesticides (0%). We investigated whether this could indicate actual development of SP-resistance in cattle ticks. First, using the larval packet test technique, we confirmed that the computation of LC50 and LC90 was repeatable and remained stable across generations of the Rhipicephalus (Boophilus) geigyi Houndé laboratory strain. We then collected from the field fully-engorged female R. geigyi to evaluate the SP-resistance relative to the Houndé reference strain. We did not detect any case of SP-resistance in the field-derived R. geigyi ticks.

Distribution patterns of three sodium channel mutations associated with pyrethroid resistance in Rhipicephalus (Boophilus) microplus populations from North and South America, South Africa and Australia

Resistance to synthetic pyrethroids (SP) in the cattle tick Rhipicephalus (Boophilus) microplus is widespread throughout its distribution area. Three single nucleotide substitutions identified in Domains II and III of the sodium channel gene of R. (B.) microplus are known to be associated with target site pyrethroid resistance. We developed a multiplex PCR using allele-specific primers to amplify wild type or mutated genotypes of the three mutations simultaneously. This assay was used to screen tick samples originating from Brazil, Argentina, Mexico, South Africa and Australia whose phenotype to flumethrin and cypermethrin had been determined by the use of the Larval Tarsal test (LTT) or the Larval Packet Test (LPT). These mutations were found to have distinct geographical distributions and result in different resistance phenotypes. The L64I Domain II mutation conferring resistance to several SP compounds was found in all the Brazilian, Argentinean and Australian populations and in one South African population, with frequencies between 38% and 100% in flumethrin and cypermethrin resistant populations. In contrast, this mutation was not found in samples from Mexico, while the Domain III mutation was found exclusively in this country. The G72V Domain II flumethrin-specific mutation was found in a single Australian population, with a very low resistant allele frequency (3%). The homozygous resistant RR genotype of the L64I Domain II mutation correlated significantly with the survival rates at the discriminating doses of flumethrin and cypermethrin. This survey shows the widespread distribution of the L64I Domain II mutation and provides evidence of its geographic separation from the Domain III mutation.

ABC transporters as a multidrug detoxification mechanism in Rhipicephalus (Boophilus) microplus

ATP-binding cassette (ABC) transporters are responsible for pumping drugs across membranes and are an important drug detoxification mechanism. Since ABC transporters act on a wide spectrum of chemical compounds, they have been associated with multidrug resistance phenotype in various parasites and cancer cells. Here, we document the presence of a Rhipicephalus (Boophilus) microplus tick population (Jaguar) resistant to four acaricide classes (organophosphates (OP), synthetic pyrethroids (SP), amitraz and macrocyclic lactones (ML)) and reveal that the cattle tick has a multidrug detoxification mechanism based on ABC transporter proteins. Acaricide toxicity was assessed using the larval packet test (LPT), and mortality data were subjected to probit analysis using a susceptible strain (POA) as reference. Larvae were pre-exposed to sub-lethal doses of the ABC-transporter inhibitors, cyclosporin A (CsA) and MK571, and subsequently treated with ivermectin, abamectin, moxidectin, chlorpyriphos, cypermethrin, or amitraz in LPT. Results show that lethal concentrations 50 % (LC(50)) of ivermectin, abamectin, moxidectin (MLs), and chlorpyriphos (OP) were significantly reduced in larvae exposed to CsA and MK571 inhibitors in the Jaguar resistant population, but LC(50) did not change in POA susceptible strain larvae. LC(50) of cypermetrin (SP) and amitraz remained unchanged in inhibitor-exposed larvae, compared to larvae from Jaguar and POA strains not exposed to inhibitor. These results suggest that ABC transporter proteins can protect ticks against a wide range of acaricides and have an important implication in drug resistance development as a multidrug detoxification mechanism.

Spectroscopic evaluation of thymol dissolved by different methods and influence on acaricidal activity against larvae of Rhipicephalus microplus (Acari: Ixodidae)

The acaricidal activity of three thymol formulations was investigated at five concentrations (1.25, 2.5, 5.0, 7.5, and 10.0 mg/ml) on Rhipicephalus microplus larvae, and the behavior of its solubility in these formulations was analyzed. The thymol was dissolved in distilled water plus 1 % dimethylsulfoxide as adjuvant under two heating regimes (water bath in formulation 1 and hot plate in formulation 2) as well as without heating in 50 % ethanol and 50 % water (v/v). The acaricidal activity was assessed by the modified larval packet test, and the solubilization behavior was investigated by ultraviolet-visible spectroscopy, based on the Beer-Lambert law. With formulations 1 and 2, the mortality was greater than 95 % starting at the thymol concentrations of 5.0 and 7.5 mg/ml, respectively, while with formulation 3, this mortality level was reached starting at a concentration of 2.5 mg/ml, showing that the addition of ethanol in the solution enhanced the acaricidal action of thymol. This result was supported by the LC 90 values, which were 3.3, 2.4, and 1.6 mg/ml of thymol for formulations 1, 2, and 3, respectively. This result is related to the better solubility of thymol in the hydroethanolic formulation, since the spectroscopic analysis revealed that the thymol dissolved more completely in this formulation. This fact was evident once the R (2) obtained from the linear regression analysis of the relation absorbance × concentration of the formulations 1, 2, and 3 approached the optimal value (R (2) = 1) in the following sequence: 1, 2, and 3 (0.717, 0.901, and 0.968, respectively).

Acaricide resistance status in Indian isolates of Hyalomma anatolicum

The multi host tick, Hyalomma anatolicum, is the commonest Hyalomma species in India and cattle serves as the main host of this species. A study to evaluate the acaricide resistance of H. anatolicum to deltamethrin, cypermethrin and diazinon was conducted in 20 areas located in three agro climatic regions known to have abundance of the species. Results obtained by the "larval packet test" (LPT) showed a low grade resistance (level-I, RF <5) in the tick species to both deltamethrin and cypermethrin in 10 areas and higher grade resistance (level-II, RF <25) to deltamethrin in one area, where intensive use of synthetic pyrethroids are practiced for tick control. Low grade resistance to diazinon (level I) was recorded in six areas where organophosphates compounds are extensively used for agricultural practices allowing increased exposure of the moulting instars of the ticks to these chemicals. Biochemical analysis of the samples suggested involvement of esterase and alterations of acetylcholinesterase in the resistance mechanisms.

Acaricidal activity of eugenol on Rhipicephalus microplus (Acari: Ixodidae) and Dermacentor nitens (Acari: Ixodidae) larvae

The aim of this study was to evaluate the acaricidal activity of eugenol, with different solubilizations and concentrations, on Rhipicephalus microplus and Dermacentor nitens larvae and to determine the lethal time. The study consisted of four experiments, and the mortality was assessed using the larval packet test with adaptations. The mortality observed in the first experiment was 100 % for all the groups treated with eugenol solubilized in different solvents. In the second, the hydroethanolic formulation of eugenol was used, and the mortality rates for R. microplus and D. nitens was 100 % starting from the concentration of 5.0 μl/ml. In the third experiment, the mortality was 100 % for larvae of both R. microplus and D. nitens after 1 h of contact. And in the fourth experiment, the mortality was above 90 % and statistically similar (p > 0.05) for the four methods the test evaluated.

Acaricidal activity of the essential oils from three Lamiaceae plant species on Rhipicephalus turanicus Pom. (Acari: Ixodidae)

Acaricidal effects of three Labiatae essential oils extracted from ariel parts of Thymus sipyleus Boiss. subsp. sipyleus, Mentha longifolia L., and Dorystoechas hastata Boiss. & Heldr. ex Bentham on 10-day-old Rhipicephalus turanicus Pom. (Acari: Ixodidae) larvae were evaluated by using the larval packet test bioassay. Serial dilutions of the three essential oils were tested from a starting concentration of 1-0.1% (1.0, 0.5, 0.25, and 0.1% w/v). Results showed that all essential oils had very similar activity, producing complete mortality (100%) in all tested concentrations on 10-day-old R. turanicus tick larvae.

Survey of pyrethroid and organophosphate resistance in Brazilian field populations of Rhipicephalus (Boophilus) microplus: Detection of C190A mutation in domain II of the para-type sodium channel gene

The cattle tick Rhipicephalus (Boophilus) microplus causes expressive damage to livestock in Brazil and other countries. Its control is becoming more difficult due to the development of resistance in populations. Early detection of resistance can help in developing effective control strategies. This study evaluated the susceptibility of R. microplus to cypermethrin and chlorpyriphos and was the first attempt to identify the mechanism of resistance (target site insensitivity) in cattle tick populations from Minas Gerais state (Southeastern Brazil). Engorged female ticks were collected from 10 ranches within the state of Minas Gerais, and susceptibility was evaluated with the larval packet test (LPT) using technical grade cypermethrin and chlorpyriphos. It was possible to analyze LPT results of seven populations. Target site insensitivity was investigated in all 10 isolates by using molecular approaches for detection of the T2134A substitution within the domain III S6 segment and the C190A in the domain II S4-5 linker from the para-type sodium channel gene. LPT showed that all seven populations were resistant to cypermethrin with resistance ratio (RR) ranging from 16.0 to 25.0 and 85.7% were resistant to chlorpyriphos (RR=2.2–15.6). Although the T2134A mutation was not detected, the C190A mutation was highly prevalent, being present in 82–100% of the alleles sampled in field populations. A significant correlation was found between the LC50 values for cypermethrin and the frequency of the C190A mutation suggesting that it might be responsible for the phenotypic resistance detected.

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

A cross sectional study was conducted to assess the prevalence of synthetic pyrethroids (SP) resistance in Rhipicephalus (Boophilus) microplus in India. Twenty-seven areas located in six agro-climatic regions were selected for the collection of engorged ticks using two stage stratified sampling procedure.Adult immersion test (AIT) and larval packet test (LPT) were optimized using laboratory reared susceptible line of R.(B.) microplus (IVRI-I) for determination of 95% lethal concentration (LC95) of deltamethrin (29.6ppm in AIT and 35.5ppm in LPT) and cypermethrin (349.1ppm in AIT and 350.7ppm in LPT). The AIT with a discriminating dose (2× LC95) was used to detect deltamethrin and cypermethrin resistance in the field isolates of R.(B.) microplus.On the basis of the data generated on three variables viz., mortality, egg masses and reproductive index, the resistance level was categorized as I, II, III and IV. The overall prevalence of SP-resistant R.(B.) microplus among the sampled farms was 66.6% (18/27). Out of these 18 areas, resistance to deltamethrin at level I was detected in 08 areas (resistance factor=2.0–4.9), at level II in 09 areas (RF=5.2–11.8), at level III in 01 area (RF=34.9) and at level IV in 01 area (RF=95.7). The resistance to cypermethrin was detected in 16 areas and level of resistance was detected at level I in 10 areas (RF=2.06–4.64) and at level II in 06 areas (RF=5.13–9.88). The middle-gangetic and trans-gangetic plains revealed higher density of resistant ticks where intensive cross bred cattle population are reared and the SP compounds are commonly used. The data generated on acaricide resistant status in ticks will help in formulating tick control strategy for the country.

Toxicity of solvents and surfactants to Amblyomma cajennense (Fabricius, 1787) (Acari: Ixodidae) and Dermacentor nitens (Neumann, 1897) (Acari: Ixodidae) larvae

The objective of this work was to verify the sensitivity of Amblyomma cajennense and Dermacentor nitens larvae to the solvents ethanol, methanol, acetone, xylol and dimethyl sulfoxide (DMSO) and the surfactant Tween 80. The first four solvents were tested at analytical purity while the DMSO and surfactant Tween 80 were tested at a concentration of 1%. The substances tested at analytical purity that caused high mortality were also tested at concentrations of 50%, 25% and 1%. The larval packet test was used, with 10 repetitions for each treatment. A control group was also formed with the same number of repetitions, in which the larvae were only exposed to distilled water. In the first experiment, only xylol was highly toxic at the concentrations tested, causing mortality above 90% for larvae of both species. In the second experiment, xylol at 1% and at 25% showed low toxicity to the A. cajennense and D. nitens larvae, respectively, since the percentage mortality was statistically similar to that of the control group (p>0.05).

Study of acariasis in cattle and ticks resistance against cypermethrin in Al-Najaf province

The present study was carried out at September 2010 to evaluated tick infestation of cattle in Al-Najaf province with diagnosis of cypermethrin resistance by using FAO larval packet test and modified larval packet test. The result showed that the infestation rate of acariasis was 54.34%. The identification of ticks revealed that 55.06% of collected ticks were Hayaloma spp., while the percentage of Boophilus spp. and Rhipicephalus spp. Were 31.86% and 13.08% respectively. According to site of infestation, the highest percentage was recorded in udder 45%, followed by perineal region 25%, head –neck 18% and others 7%. The LPT results showed there was no significant variation (P≤0.01) between the mortality rates of Boophilus (96.42%) and Hyaloma (96.72%) at recommended dose. In other hand, the MLPT method showed that the mortality rate of Boophilus larvae at recommended and double recommended doses were 94.82% and 98.04% respectively, while all the Hyaloma larvae were killed at the recommended dose.