The Experts below are selected from a list of 34869 Experts worldwide ranked by ideXlab platform
John E George - One of the best experts on this subject based on the ideXlab platform.
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in vitro and in vivo evaluation of deltamethrin and amitraz mixtures for the control of rhipicephalus boophilus microplus acari ixodidae in new caledonia
Veterinary Parasitology, 2008Co-Authors: Nicolas Barré, Ronald B Davey, Andrew Y Li, Huguette Gaia, Jeanmichel Delathiere, Robert J Miller, John E GeorgeAbstract:Acaricide resistance is a major problem that hinders the control of the tropical cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini), in many parts of the world where cattle production continues to suffer severe economic losses to tick infestation. Deltamethrin and amitraz have been used alone to control R. microplus in New Caledonia for the past decade, and tick populations have developed resistance to both acaricides. A study was conducted to evaluate the effectiveness of deltamethrin and amitraz mixtures, through in vitro laboratory bioassays and in vivo on-animal efficacy trials, for the control of resistant R. microplus on cattle at two dairy farms in New Caledonia. Results of laboratory bioassays using modified larval packet tests (LPT) revealed up to 16.59-fold resistance to deltamethrin, and up to 5.86-fold resistance to amitraz. Significant Synergism was observed when amitraz was used as a synergist in deltamethrin bioassays. Amitraz significantly increased deltamethrin toxicity to tick larvae, while deltamethrin was much less effective on amitraz toxicity. Synergism of amitraz by deltamethrin only occurred when the deltamethrin concentration was relatively high. Results of on animal efficacy trials of deltamethrin and amitraz alone and mixtures of both at different concentrations revealed a similar pattern of Synergism. Adding amitraz to a deltamethrin formulation led to dramatic increases of percent reduction of both immature and adult ticks. In contrast, adding deltamethrin to an amitraz formulation did not increase control efficacy. Results from this study may lead to the adoption of an acaricide mixture strategy for the control of pyrethroid-resistant R. microplus in New Caledonia and elsewhere.
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acaricide resistance and Synergism between permethrin and amitraz against susceptible and resistant strains of boophilus microplus acari ixodidae
Pest Management Science, 2007Co-Authors: Andrew Y Li, Ronald B Davey, Andrew C Chen, Robert J Miller, John E GeorgeAbstract:The control of the southern cattle tick, Boophilus microplus (Canestrini), in Mexico and many other countries relies on chemical acaricides. Boophilus microplus has developed resistance to all major classes of acaricides in recent years. To gain a better understanding of the resistance and to develop resistance management strategies that benefit both Mexican ranchers and USDA's cattle fever tick eradication program (CFTEP), the authors used larval bioassay techniques to determine levels of resistance to permethrin and amitraz and then evaluated Synergism between these two acaricides in one susceptible laboratory tick strain and four resistant strains originating from Mexico and Brazil. To examine mechanisms of resistance to permethrin in these strains, the frequency of a mutated sodium channel gene was determined using a PCR assay. The tick strains from Mexico and Brazil demonstrated 49.4- to over 672.2-fold resistance to permethrin, and up to 94.5-fold resistance to amitraz. While the San Roman strain from Mexico was the most permethrin-resistant strain, the Santa Luiza strain from Brazil was the most amitraz-resistant strain. A significant correlation was found between the permethrin resistance ratio and the allelic frequency of the sodium channel mutation. Significant Synergism between permethrin and amitraz was found when one acaricide was tested in the presence of another. Synergism ratios ranged from 1.5 to 54.9 when amitraz was tested as a synergist for permethrin. Similar Synergism ratios were obtained when permethrin was tested as a synergist for amitraz. Permethrin caused virtually no mortality in the San Roman strain, even at the highest concentration (3294 µg cm−2). Adding amitraz (11.0 µg cm−2) to permethrin led to a dramatic increase in larval mortality, even at very low concentrations of permethrin. Copyright © 2007 Society of Chemical Industry
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acaricide resistance and Synergism between permethrin and amitraz against susceptible and resistant strains of boophilus microplus acari ixodidae
Pest Management Science, 2007Co-Authors: Andrew C Chen, Ronald B Davey, Robert J Miller, John E GeorgeAbstract:The control of the southern cattle tick, Boophilus microplus (Canestrini), in Mexico and many other countries relies on chemical acaricides. Boophilus microplus has developed resistance to all major classes of acaricides in recent years. To gain a better understanding of the resistance and to develop resistance management strategies that benefit both Mexican ranchers and USDA's cattle fever tick eradication program (CFTEP), the authors used larval bioassay techniques to determine levels of resistance to permethrin and amitraz and then evaluated Synergism between these two acaricides in one susceptible laboratory tick strain and four resistant strains originating from Mexico and Brazil. To examine mechanisms of resistance to permethrin in these strains, the frequency of a mutated sodium channel gene was determined using a PCR assay. The tick strains from Mexico and Brazil demonstrated 49.4- to over 672.2-fold resistance to permethrin, and up to 94.5-fold resistance to amitraz. While the San Roman strain from Mexico was the most permethrin-resistant strain, the Santa Luiza strain from Brazil was the most amitraz-resistant strain. A significant correlation was found between the permethrin resistance ratio and the allelic frequency of the sodium channel mutation. Significant Synergism between permethrin and amitraz was found when one acaricide was tested in the presence of another. Synergism ratios ranged from 1.5 to 54.9 when amitraz was tested as a synergist for permethrin. Similar Synergism ratios were obtained when permethrin was tested as a synergist for amitraz. Permethrin caused virtually no mortality in the San Roman strain, even at the highest concentration (3294 microg cm(-2)). Adding amitraz (11.0 microg cm(-2)) to permethrin led to a dramatic increase in larval mortality, even at very low concentrations of permethrin.
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resistance to coumaphos and diazinon in boophilus microplus acari ixodidae and evidence for the involvement of an oxidative detoxification mechanism
Journal of Medical Entomology, 2003Co-Authors: Andrew Y Li, Ronald B Davey, Robert J Miller, John E GeorgeAbstract:The levels of resistance to two organophosphate acaricides, coumaphos and diazinon, in several Mexican strains of Boophilus microplus (Canestrini) were evaluated using the FAO larval packet test. Regression analysis of LC50 data revealed a signiÞcant cross-resistance pattern between those two acaricides. Metabolic mechanisms of resistance were investigated with synergist bioassays. Piperonyl butoxide (PBO) reduced coumaphos toxicity in susceptible strains, but synergized cou- maphos toxicity in resistant strains. There was a signiÞcant correlation between PBO Synergism ratios and the coumaphos resistance ratios. The results suggest that an enhanced cytochrome P450 mono- oxygenase (cytP450)-mediated detoxiÞcation mechanism may exist in the resistant strains, in addition to the cytP450-mediated metabolic pathway that activates coumaphos. PBO failed to synergize diazinon toxicity in resistant strains, suggesting the cytP450 involved in detoxiÞcation were speciÞc. Triphenylphosphate (TPP) synergized toxicity of both acaricides in both susceptible and resistant strains, and there was no correlation between TPP Synergism ratios and the LC50 estimates for either acaricide. Esterases may not play a major role in resistance to coumaphos and diazinon in those strains. Bioassays with diethyl maleate (DEM) revealed a signiÞcant correlation between DEM Synergism ratios and LC50 estimates for diazinon, suggesting a possible role for glutathione S-transferases in diazinon detoxiÞcation. Resistance to coumaphos in the Mexican strains of B. microplus was likely to be conferred by both acytP450-mediated detoxiÞcation mechanism described here and the mechanism of insensitive acetylcholinesterases reported elsewhere. The results of this study also underscore the potential risk of coumaphos resistance in B. microplus from Mexico to the U.S. cattle fever tick eradication program.
Erica Palesandro - One of the best experts on this subject based on the ideXlab platform.
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PARP1 expression drives the synergistic antitumor activity of trabectedin and PARP1 inhibitors in sarcoma preclinical models
Molecular Cancer, 2017Co-Authors: Ymera Pignochino, Lorenzo D’ambrosio, Carmine Dell’aglio, Marco Basiricò, Marta Canta, Francesca Vignolo Lutati, Sandra Aliberti, Federica Capozzi, Annalisa Lorenzato, Erica PalesandroAbstract:BackgroundEnhancing the antitumor activity of the DNA-damaging drugs is an attractive strategy to improve current treatment options. Trabectedin is an isoquinoline alkylating agent with a peculiar mechanism of action. It binds to minor groove of DNA inducing single- and double-strand-breaks. These kinds of damage lead to the activation of PARP1, a first-line enzyme in DNA-damage response pathways. We hypothesized that PARP1 targeting could perpetuate trabectedin-induced DNA damage in tumor cells leading finally to cell death.MethodsWe investigated trabectedin and PARP1 inhibitor Synergism in several tumor histotypes both in vitro and in vivo (subcutaneous and orthotopic tumor xenografts in mice). We searched for key determinants of drug Synergism by comparative genomic hybridization (aCGH) and gene expression profiling (GEP) and validated their functional role.ResultsTrabectedin activated PARP1 enzyme and the combination with PARP1 inhibitors potentiated DNA damage, cell cycle arrest at G2/M checkpoint and apoptosis, if compared to single agents. Olaparib was the most active PARP1 inhibitor to combine with trabectedin and we confirmed the antitumor and antimetastatic activity of trabectedin/olaparib combination in mice models. However, we observed different degree of trabectedin/olaparib Synergism among different cell lines. Namely, in DMR leiomyosarcoma models the combination was significantly more active than single agents, while in SJSA-1 osteosarcoma models no further advantage was obtained if compared to trabectedin alone. aCGH and GEP revealed that key components of DNA-repair pathways were involved in trabectedin/olaparib Synergism. In particular, PARP1 expression dictated the degree of the Synergism. Indeed, trabectedin/olaparib Synergism was increased after PARP1 overexpression and reduced after PARP1 silencing.ConclusionsPARP1 inhibition potentiated trabectedin activity in a PARP1-dependent manner and PARP1 expression in tumor cells might be a useful predictive biomarker that deserves clinical evaluation.
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PARP1 expression drives the synergistic antitumor activity of trabectedin and PARP1 inhibitors in sarcoma preclinical models
Molecular cancer, 2017Co-Authors: Ymera Pignochino, Marco Basiricò, Marta Canta, Sandra Aliberti, Federica Capozzi, Annalisa Lorenzato, Lorenzo D'ambrosio, Carmine Dell'aglio, Francesca Vignolo Lutati, Erica PalesandroAbstract:Enhancing the antitumor activity of the DNA-damaging drugs is an attractive strategy to improve current treatment options. Trabectedin is an isoquinoline alkylating agent with a peculiar mechanism of action. It binds to minor groove of DNA inducing single- and double-strand-breaks. These kinds of damage lead to the activation of PARP1, a first-line enzyme in DNA-damage response pathways. We hypothesized that PARP1 targeting could perpetuate trabectedin-induced DNA damage in tumor cells leading finally to cell death. We investigated trabectedin and PARP1 inhibitor Synergism in several tumor histotypes both in vitro and in vivo (subcutaneous and orthotopic tumor xenografts in mice). We searched for key determinants of drug Synergism by comparative genomic hybridization (aCGH) and gene expression profiling (GEP) and validated their functional role. Trabectedin activated PARP1 enzyme and the combination with PARP1 inhibitors potentiated DNA damage, cell cycle arrest at G2/M checkpoint and apoptosis, if compared to single agents. Olaparib was the most active PARP1 inhibitor to combine with trabectedin and we confirmed the antitumor and antimetastatic activity of trabectedin/olaparib combination in mice models. However, we observed different degree of trabectedin/olaparib Synergism among different cell lines. Namely, in DMR leiomyosarcoma models the combination was significantly more active than single agents, while in SJSA-1 osteosarcoma models no further advantage was obtained if compared to trabectedin alone. aCGH and GEP revealed that key components of DNA-repair pathways were involved in trabectedin/olaparib Synergism. In particular, PARP1 expression dictated the degree of the Synergism. Indeed, trabectedin/olaparib Synergism was increased after PARP1 overexpression and reduced after PARP1 silencing. PARP1 inhibition potentiated trabectedin activity in a PARP1-dependent manner and PARP1 expression in tumor cells might be a useful predictive biomarker that deserves clinical evaluation.
Ymera Pignochino - One of the best experts on this subject based on the ideXlab platform.
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PARP1 expression drives the synergistic antitumor activity of trabectedin and PARP1 inhibitors in sarcoma preclinical models
Molecular Cancer, 2017Co-Authors: Ymera Pignochino, Lorenzo D’ambrosio, Carmine Dell’aglio, Marco Basiricò, Marta Canta, Francesca Vignolo Lutati, Sandra Aliberti, Federica Capozzi, Annalisa Lorenzato, Erica PalesandroAbstract:BackgroundEnhancing the antitumor activity of the DNA-damaging drugs is an attractive strategy to improve current treatment options. Trabectedin is an isoquinoline alkylating agent with a peculiar mechanism of action. It binds to minor groove of DNA inducing single- and double-strand-breaks. These kinds of damage lead to the activation of PARP1, a first-line enzyme in DNA-damage response pathways. We hypothesized that PARP1 targeting could perpetuate trabectedin-induced DNA damage in tumor cells leading finally to cell death.MethodsWe investigated trabectedin and PARP1 inhibitor Synergism in several tumor histotypes both in vitro and in vivo (subcutaneous and orthotopic tumor xenografts in mice). We searched for key determinants of drug Synergism by comparative genomic hybridization (aCGH) and gene expression profiling (GEP) and validated their functional role.ResultsTrabectedin activated PARP1 enzyme and the combination with PARP1 inhibitors potentiated DNA damage, cell cycle arrest at G2/M checkpoint and apoptosis, if compared to single agents. Olaparib was the most active PARP1 inhibitor to combine with trabectedin and we confirmed the antitumor and antimetastatic activity of trabectedin/olaparib combination in mice models. However, we observed different degree of trabectedin/olaparib Synergism among different cell lines. Namely, in DMR leiomyosarcoma models the combination was significantly more active than single agents, while in SJSA-1 osteosarcoma models no further advantage was obtained if compared to trabectedin alone. aCGH and GEP revealed that key components of DNA-repair pathways were involved in trabectedin/olaparib Synergism. In particular, PARP1 expression dictated the degree of the Synergism. Indeed, trabectedin/olaparib Synergism was increased after PARP1 overexpression and reduced after PARP1 silencing.ConclusionsPARP1 inhibition potentiated trabectedin activity in a PARP1-dependent manner and PARP1 expression in tumor cells might be a useful predictive biomarker that deserves clinical evaluation.
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PARP1 expression drives the synergistic antitumor activity of trabectedin and PARP1 inhibitors in sarcoma preclinical models
Molecular cancer, 2017Co-Authors: Ymera Pignochino, Marco Basiricò, Marta Canta, Sandra Aliberti, Federica Capozzi, Annalisa Lorenzato, Lorenzo D'ambrosio, Carmine Dell'aglio, Francesca Vignolo Lutati, Erica PalesandroAbstract:Enhancing the antitumor activity of the DNA-damaging drugs is an attractive strategy to improve current treatment options. Trabectedin is an isoquinoline alkylating agent with a peculiar mechanism of action. It binds to minor groove of DNA inducing single- and double-strand-breaks. These kinds of damage lead to the activation of PARP1, a first-line enzyme in DNA-damage response pathways. We hypothesized that PARP1 targeting could perpetuate trabectedin-induced DNA damage in tumor cells leading finally to cell death. We investigated trabectedin and PARP1 inhibitor Synergism in several tumor histotypes both in vitro and in vivo (subcutaneous and orthotopic tumor xenografts in mice). We searched for key determinants of drug Synergism by comparative genomic hybridization (aCGH) and gene expression profiling (GEP) and validated their functional role. Trabectedin activated PARP1 enzyme and the combination with PARP1 inhibitors potentiated DNA damage, cell cycle arrest at G2/M checkpoint and apoptosis, if compared to single agents. Olaparib was the most active PARP1 inhibitor to combine with trabectedin and we confirmed the antitumor and antimetastatic activity of trabectedin/olaparib combination in mice models. However, we observed different degree of trabectedin/olaparib Synergism among different cell lines. Namely, in DMR leiomyosarcoma models the combination was significantly more active than single agents, while in SJSA-1 osteosarcoma models no further advantage was obtained if compared to trabectedin alone. aCGH and GEP revealed that key components of DNA-repair pathways were involved in trabectedin/olaparib Synergism. In particular, PARP1 expression dictated the degree of the Synergism. Indeed, trabectedin/olaparib Synergism was increased after PARP1 overexpression and reduced after PARP1 silencing. PARP1 inhibition potentiated trabectedin activity in a PARP1-dependent manner and PARP1 expression in tumor cells might be a useful predictive biomarker that deserves clinical evaluation.
Robert J Miller - One of the best experts on this subject based on the ideXlab platform.
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in vitro and in vivo evaluation of deltamethrin and amitraz mixtures for the control of rhipicephalus boophilus microplus acari ixodidae in new caledonia
Veterinary Parasitology, 2008Co-Authors: Nicolas Barré, Ronald B Davey, Andrew Y Li, Huguette Gaia, Jeanmichel Delathiere, Robert J Miller, John E GeorgeAbstract:Acaricide resistance is a major problem that hinders the control of the tropical cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini), in many parts of the world where cattle production continues to suffer severe economic losses to tick infestation. Deltamethrin and amitraz have been used alone to control R. microplus in New Caledonia for the past decade, and tick populations have developed resistance to both acaricides. A study was conducted to evaluate the effectiveness of deltamethrin and amitraz mixtures, through in vitro laboratory bioassays and in vivo on-animal efficacy trials, for the control of resistant R. microplus on cattle at two dairy farms in New Caledonia. Results of laboratory bioassays using modified larval packet tests (LPT) revealed up to 16.59-fold resistance to deltamethrin, and up to 5.86-fold resistance to amitraz. Significant Synergism was observed when amitraz was used as a synergist in deltamethrin bioassays. Amitraz significantly increased deltamethrin toxicity to tick larvae, while deltamethrin was much less effective on amitraz toxicity. Synergism of amitraz by deltamethrin only occurred when the deltamethrin concentration was relatively high. Results of on animal efficacy trials of deltamethrin and amitraz alone and mixtures of both at different concentrations revealed a similar pattern of Synergism. Adding amitraz to a deltamethrin formulation led to dramatic increases of percent reduction of both immature and adult ticks. In contrast, adding deltamethrin to an amitraz formulation did not increase control efficacy. Results from this study may lead to the adoption of an acaricide mixture strategy for the control of pyrethroid-resistant R. microplus in New Caledonia and elsewhere.
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acaricide resistance and Synergism between permethrin and amitraz against susceptible and resistant strains of boophilus microplus acari ixodidae
Pest Management Science, 2007Co-Authors: Andrew Y Li, Ronald B Davey, Andrew C Chen, Robert J Miller, John E GeorgeAbstract:The control of the southern cattle tick, Boophilus microplus (Canestrini), in Mexico and many other countries relies on chemical acaricides. Boophilus microplus has developed resistance to all major classes of acaricides in recent years. To gain a better understanding of the resistance and to develop resistance management strategies that benefit both Mexican ranchers and USDA's cattle fever tick eradication program (CFTEP), the authors used larval bioassay techniques to determine levels of resistance to permethrin and amitraz and then evaluated Synergism between these two acaricides in one susceptible laboratory tick strain and four resistant strains originating from Mexico and Brazil. To examine mechanisms of resistance to permethrin in these strains, the frequency of a mutated sodium channel gene was determined using a PCR assay. The tick strains from Mexico and Brazil demonstrated 49.4- to over 672.2-fold resistance to permethrin, and up to 94.5-fold resistance to amitraz. While the San Roman strain from Mexico was the most permethrin-resistant strain, the Santa Luiza strain from Brazil was the most amitraz-resistant strain. A significant correlation was found between the permethrin resistance ratio and the allelic frequency of the sodium channel mutation. Significant Synergism between permethrin and amitraz was found when one acaricide was tested in the presence of another. Synergism ratios ranged from 1.5 to 54.9 when amitraz was tested as a synergist for permethrin. Similar Synergism ratios were obtained when permethrin was tested as a synergist for amitraz. Permethrin caused virtually no mortality in the San Roman strain, even at the highest concentration (3294 µg cm−2). Adding amitraz (11.0 µg cm−2) to permethrin led to a dramatic increase in larval mortality, even at very low concentrations of permethrin. Copyright © 2007 Society of Chemical Industry
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acaricide resistance and Synergism between permethrin and amitraz against susceptible and resistant strains of boophilus microplus acari ixodidae
Pest Management Science, 2007Co-Authors: Andrew C Chen, Ronald B Davey, Robert J Miller, John E GeorgeAbstract:The control of the southern cattle tick, Boophilus microplus (Canestrini), in Mexico and many other countries relies on chemical acaricides. Boophilus microplus has developed resistance to all major classes of acaricides in recent years. To gain a better understanding of the resistance and to develop resistance management strategies that benefit both Mexican ranchers and USDA's cattle fever tick eradication program (CFTEP), the authors used larval bioassay techniques to determine levels of resistance to permethrin and amitraz and then evaluated Synergism between these two acaricides in one susceptible laboratory tick strain and four resistant strains originating from Mexico and Brazil. To examine mechanisms of resistance to permethrin in these strains, the frequency of a mutated sodium channel gene was determined using a PCR assay. The tick strains from Mexico and Brazil demonstrated 49.4- to over 672.2-fold resistance to permethrin, and up to 94.5-fold resistance to amitraz. While the San Roman strain from Mexico was the most permethrin-resistant strain, the Santa Luiza strain from Brazil was the most amitraz-resistant strain. A significant correlation was found between the permethrin resistance ratio and the allelic frequency of the sodium channel mutation. Significant Synergism between permethrin and amitraz was found when one acaricide was tested in the presence of another. Synergism ratios ranged from 1.5 to 54.9 when amitraz was tested as a synergist for permethrin. Similar Synergism ratios were obtained when permethrin was tested as a synergist for amitraz. Permethrin caused virtually no mortality in the San Roman strain, even at the highest concentration (3294 microg cm(-2)). Adding amitraz (11.0 microg cm(-2)) to permethrin led to a dramatic increase in larval mortality, even at very low concentrations of permethrin.
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resistance to coumaphos and diazinon in boophilus microplus acari ixodidae and evidence for the involvement of an oxidative detoxification mechanism
Journal of Medical Entomology, 2003Co-Authors: Andrew Y Li, Ronald B Davey, Robert J Miller, John E GeorgeAbstract:The levels of resistance to two organophosphate acaricides, coumaphos and diazinon, in several Mexican strains of Boophilus microplus (Canestrini) were evaluated using the FAO larval packet test. Regression analysis of LC50 data revealed a signiÞcant cross-resistance pattern between those two acaricides. Metabolic mechanisms of resistance were investigated with synergist bioassays. Piperonyl butoxide (PBO) reduced coumaphos toxicity in susceptible strains, but synergized cou- maphos toxicity in resistant strains. There was a signiÞcant correlation between PBO Synergism ratios and the coumaphos resistance ratios. The results suggest that an enhanced cytochrome P450 mono- oxygenase (cytP450)-mediated detoxiÞcation mechanism may exist in the resistant strains, in addition to the cytP450-mediated metabolic pathway that activates coumaphos. PBO failed to synergize diazinon toxicity in resistant strains, suggesting the cytP450 involved in detoxiÞcation were speciÞc. Triphenylphosphate (TPP) synergized toxicity of both acaricides in both susceptible and resistant strains, and there was no correlation between TPP Synergism ratios and the LC50 estimates for either acaricide. Esterases may not play a major role in resistance to coumaphos and diazinon in those strains. Bioassays with diethyl maleate (DEM) revealed a signiÞcant correlation between DEM Synergism ratios and LC50 estimates for diazinon, suggesting a possible role for glutathione S-transferases in diazinon detoxiÞcation. Resistance to coumaphos in the Mexican strains of B. microplus was likely to be conferred by both acytP450-mediated detoxiÞcation mechanism described here and the mechanism of insensitive acetylcholinesterases reported elsewhere. The results of this study also underscore the potential risk of coumaphos resistance in B. microplus from Mexico to the U.S. cattle fever tick eradication program.
Ronald B Davey - One of the best experts on this subject based on the ideXlab platform.
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in vitro and in vivo evaluation of deltamethrin and amitraz mixtures for the control of rhipicephalus boophilus microplus acari ixodidae in new caledonia
Veterinary Parasitology, 2008Co-Authors: Nicolas Barré, Ronald B Davey, Andrew Y Li, Huguette Gaia, Jeanmichel Delathiere, Robert J Miller, John E GeorgeAbstract:Acaricide resistance is a major problem that hinders the control of the tropical cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini), in many parts of the world where cattle production continues to suffer severe economic losses to tick infestation. Deltamethrin and amitraz have been used alone to control R. microplus in New Caledonia for the past decade, and tick populations have developed resistance to both acaricides. A study was conducted to evaluate the effectiveness of deltamethrin and amitraz mixtures, through in vitro laboratory bioassays and in vivo on-animal efficacy trials, for the control of resistant R. microplus on cattle at two dairy farms in New Caledonia. Results of laboratory bioassays using modified larval packet tests (LPT) revealed up to 16.59-fold resistance to deltamethrin, and up to 5.86-fold resistance to amitraz. Significant Synergism was observed when amitraz was used as a synergist in deltamethrin bioassays. Amitraz significantly increased deltamethrin toxicity to tick larvae, while deltamethrin was much less effective on amitraz toxicity. Synergism of amitraz by deltamethrin only occurred when the deltamethrin concentration was relatively high. Results of on animal efficacy trials of deltamethrin and amitraz alone and mixtures of both at different concentrations revealed a similar pattern of Synergism. Adding amitraz to a deltamethrin formulation led to dramatic increases of percent reduction of both immature and adult ticks. In contrast, adding deltamethrin to an amitraz formulation did not increase control efficacy. Results from this study may lead to the adoption of an acaricide mixture strategy for the control of pyrethroid-resistant R. microplus in New Caledonia and elsewhere.
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acaricide resistance and Synergism between permethrin and amitraz against susceptible and resistant strains of boophilus microplus acari ixodidae
Pest Management Science, 2007Co-Authors: Andrew Y Li, Ronald B Davey, Andrew C Chen, Robert J Miller, John E GeorgeAbstract:The control of the southern cattle tick, Boophilus microplus (Canestrini), in Mexico and many other countries relies on chemical acaricides. Boophilus microplus has developed resistance to all major classes of acaricides in recent years. To gain a better understanding of the resistance and to develop resistance management strategies that benefit both Mexican ranchers and USDA's cattle fever tick eradication program (CFTEP), the authors used larval bioassay techniques to determine levels of resistance to permethrin and amitraz and then evaluated Synergism between these two acaricides in one susceptible laboratory tick strain and four resistant strains originating from Mexico and Brazil. To examine mechanisms of resistance to permethrin in these strains, the frequency of a mutated sodium channel gene was determined using a PCR assay. The tick strains from Mexico and Brazil demonstrated 49.4- to over 672.2-fold resistance to permethrin, and up to 94.5-fold resistance to amitraz. While the San Roman strain from Mexico was the most permethrin-resistant strain, the Santa Luiza strain from Brazil was the most amitraz-resistant strain. A significant correlation was found between the permethrin resistance ratio and the allelic frequency of the sodium channel mutation. Significant Synergism between permethrin and amitraz was found when one acaricide was tested in the presence of another. Synergism ratios ranged from 1.5 to 54.9 when amitraz was tested as a synergist for permethrin. Similar Synergism ratios were obtained when permethrin was tested as a synergist for amitraz. Permethrin caused virtually no mortality in the San Roman strain, even at the highest concentration (3294 µg cm−2). Adding amitraz (11.0 µg cm−2) to permethrin led to a dramatic increase in larval mortality, even at very low concentrations of permethrin. Copyright © 2007 Society of Chemical Industry
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acaricide resistance and Synergism between permethrin and amitraz against susceptible and resistant strains of boophilus microplus acari ixodidae
Pest Management Science, 2007Co-Authors: Andrew C Chen, Ronald B Davey, Robert J Miller, John E GeorgeAbstract:The control of the southern cattle tick, Boophilus microplus (Canestrini), in Mexico and many other countries relies on chemical acaricides. Boophilus microplus has developed resistance to all major classes of acaricides in recent years. To gain a better understanding of the resistance and to develop resistance management strategies that benefit both Mexican ranchers and USDA's cattle fever tick eradication program (CFTEP), the authors used larval bioassay techniques to determine levels of resistance to permethrin and amitraz and then evaluated Synergism between these two acaricides in one susceptible laboratory tick strain and four resistant strains originating from Mexico and Brazil. To examine mechanisms of resistance to permethrin in these strains, the frequency of a mutated sodium channel gene was determined using a PCR assay. The tick strains from Mexico and Brazil demonstrated 49.4- to over 672.2-fold resistance to permethrin, and up to 94.5-fold resistance to amitraz. While the San Roman strain from Mexico was the most permethrin-resistant strain, the Santa Luiza strain from Brazil was the most amitraz-resistant strain. A significant correlation was found between the permethrin resistance ratio and the allelic frequency of the sodium channel mutation. Significant Synergism between permethrin and amitraz was found when one acaricide was tested in the presence of another. Synergism ratios ranged from 1.5 to 54.9 when amitraz was tested as a synergist for permethrin. Similar Synergism ratios were obtained when permethrin was tested as a synergist for amitraz. Permethrin caused virtually no mortality in the San Roman strain, even at the highest concentration (3294 microg cm(-2)). Adding amitraz (11.0 microg cm(-2)) to permethrin led to a dramatic increase in larval mortality, even at very low concentrations of permethrin.
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resistance to coumaphos and diazinon in boophilus microplus acari ixodidae and evidence for the involvement of an oxidative detoxification mechanism
Journal of Medical Entomology, 2003Co-Authors: Andrew Y Li, Ronald B Davey, Robert J Miller, John E GeorgeAbstract:The levels of resistance to two organophosphate acaricides, coumaphos and diazinon, in several Mexican strains of Boophilus microplus (Canestrini) were evaluated using the FAO larval packet test. Regression analysis of LC50 data revealed a signiÞcant cross-resistance pattern between those two acaricides. Metabolic mechanisms of resistance were investigated with synergist bioassays. Piperonyl butoxide (PBO) reduced coumaphos toxicity in susceptible strains, but synergized cou- maphos toxicity in resistant strains. There was a signiÞcant correlation between PBO Synergism ratios and the coumaphos resistance ratios. The results suggest that an enhanced cytochrome P450 mono- oxygenase (cytP450)-mediated detoxiÞcation mechanism may exist in the resistant strains, in addition to the cytP450-mediated metabolic pathway that activates coumaphos. PBO failed to synergize diazinon toxicity in resistant strains, suggesting the cytP450 involved in detoxiÞcation were speciÞc. Triphenylphosphate (TPP) synergized toxicity of both acaricides in both susceptible and resistant strains, and there was no correlation between TPP Synergism ratios and the LC50 estimates for either acaricide. Esterases may not play a major role in resistance to coumaphos and diazinon in those strains. Bioassays with diethyl maleate (DEM) revealed a signiÞcant correlation between DEM Synergism ratios and LC50 estimates for diazinon, suggesting a possible role for glutathione S-transferases in diazinon detoxiÞcation. Resistance to coumaphos in the Mexican strains of B. microplus was likely to be conferred by both acytP450-mediated detoxiÞcation mechanism described here and the mechanism of insensitive acetylcholinesterases reported elsewhere. The results of this study also underscore the potential risk of coumaphos resistance in B. microplus from Mexico to the U.S. cattle fever tick eradication program.
