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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 Barre, Robert J Miller, Ronald B Davey, Andrew Y Li, Huguette Gaia, Jeanmichel Delathiere, 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, Robert J Miller, Ronald B Davey, Andrew C Chen, 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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Mode of Inheritance of Amitraz Resistance in a Brazilian Strain of the Southern Cattle Tick, Boophilus microplus (Acari: Ixodidae)*
Experimental & Applied Acarology, 2005Co-Authors: Andrew Y Li, Robert J Miller, Ronald B Davey, John E GeorgeAbstract:The southern cattle tick, Boophilus microplus (Canestrini), has developed resistance to Amitraz in several countries in recent years. A study was conducted at the USDA Cattle Fever Tick Research Laboratory in Texas to investigate the mode of inheritance of Amitraz resistance with cross-mating experiments. The Muñoz strain, a laboratory reared acaricide-susceptible reference strain, was used as the susceptible parent and the Santa Luiza strain, originating in Brazil, was used as the resistant parent. A modified Food and Agriculture Organization Larval Packet Test was used to measure the levels of susceptibility of larvae of the parental strains, F_1, backcross, F_2, and F_3 generations. Results of reciprocal crossing experiments suggested that Amitraz resistance was inherited as an incomplete recessive trait. There was a strong maternal effect on larval progeny’s susceptibility to Amitraz in both the F_1 and the subsequent generations. The values of the degree of dominance were estimated at −0.156 and −0.500 for the F_1 larvae with resistant and susceptible female parents, respectively. Results of bioassays on larval progeny of the F_1 backcrossed with the resistant parent strain and that of the F_2 generations suggested that more than one gene was responsible for Amitraz resistance in the Santa Luiza strain. Comparisons of biological parameters (engorged female weight, egg mass weight, and female-to-egg weight conversion efficiency index) indicated significant differences between different genotypes. The differences appeared to be heritable, but not related to Amitraz resistance. Results from this study may have significant implications for the management of Amitraz resistance.
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mode of inheritance of Amitraz resistance in a brazilian strain of the southern cattle tick boophilus microplus acari ixodidae
Experimental and Applied Acarology, 2005Co-Authors: Andrew Y Li, Robert J Miller, Ronald B Davey, John E GeorgeAbstract:The southern cattle tick, Boophilus microplus (Canestrini), has developed resistance to Amitraz in several countries in recent years. A study was conducted at the USDA Cattle Fever Tick Research Laboratory in Texas to investigate the mode of inheritance of Amitraz resistance with cross-mating experiments. The Munoz strain, a laboratory reared acaricide-susceptible reference strain, was used as the susceptible parent and the Santa Luiza strain, originating in Brazil, was used as the resistant parent. A modified Food and Agriculture Organization Larval Packet Test was used to measure the levels of susceptibility of larvae of the parental strains, F1, backcross, F2, and F3 generations. Results of reciprocal crossing experiments suggested that Amitraz resistance was inherited as an incomplete recessive trait. There was a strong maternal effect on larval progeny’s susceptibility to Amitraz in both the F1 and the subsequent generations. The values of the degree of dominance were estimated at −0.156 and −0.500 for the F1 larvae with resistant and susceptible female parents, respectively. Results of bioassays on larval progeny of the F1 backcrossed with the resistant parent strain and that of the F2 generations suggested that more than one gene was responsible for Amitraz resistance in the Santa Luiza strain. Comparisons of biological parameters (engorged female weight, egg mass weight, and female-to-egg weight conversion efficiency index) indicated significant differences between different genotypes. The differences appeared to be heritable, but not related to Amitraz resistance. Results from this study may have significant implications for the management of Amitraz resistance.
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detection and characterization of Amitraz resistance in the southern cattle tick boophilus microplus acari ixodidae
Journal of Medical Entomology, 2004Co-Authors: Robert J Miller, Ronald B Davey, Andrew Y Li, John E GeorgeAbstract:Amitraz, a formamidine acaricide, plays an important role in the control of the southern cattle tick, Boophilus microplus (Canestrini), and other tick species that infest cattle, dogs, and wild animals. Although resistance to Amitraz in B. microplus was previously reported in several countries, the actual measurement of the level of Amitraz resistance in ticks has been difficult to determine due to the lack of a proper bioassay technique. We conducted a survey, by using a newly reported technique that was a modification of the standard Food and Agriculture Organization larval packet test, to measure the levels of resistance to Amitraz in 15 strains of B. microplus from four major cattle-producing states in Mexico. Low-order resistance (1.68- to 4.58-fold) was detected in 11 of those strains. Our laboratory selection using Amitraz on larvae of the Santa Luiza strain, which originated from Brazil, achieved a resistance ratio of 153.93 at F6, indicating the potential for high resistance to this acaricide in B. microplus. Both triphenylphosphate and piperonyl butoxide significantly synergized Amitraz toxicity in both resistant and susceptible tick strains. Diethyl maleate synergized Amitraz toxicity in one resistant strain but had no effect on the susceptible strain and had minor antagonistic effects on two other resistant strains. Target site insensitivity, instead of metabolic detoxification mechanisms, might be responsible for Amitraz resistance observed in the Santa Luiza strain and possibly in other Amitraz resistant B. microplus ticks from Mexico. The Santa Luiza strain also demonstrated high resistance to pyrethroids and moderate resistance to organophosphates. Multiple resistance shown in this strain and other B. microplus strains from Mexico poses a significant challenge to the management of B. microplus resistance to acaricides in Mexico.
Robert J Miller - One of the best experts on this subject based on the ideXlab platform.
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rotation of treatments between spinosad and Amitraz for the control of rhipicephalus boophilus microplus populations with Amitraz resistance
Veterinary Parasitology, 2010Co-Authors: N N Jonsson, Robert J Miller, D H Kemp, A Knowles, A E Ardila, R G Verrall, J T RothwellAbstract:A farmlet study was conducted over 4 years in which three treatments were applied to six groups of Holstein dairy calves. Calves in each group were infested with equal numbers of N-strain (susceptible) and Ultimo strain (Amitraz and synthetic pyrethroid resistant) tick larvae to establish self-sustaining populations with an initial, measurable level of resistance to Amitraz. Standard counts of all ticks between 4.5 and 8.0 mm diameter on one side of each animal were made each week and treatment was applied when tick numbers exceeded a threshold of 25 engorged adults per side. The three treatments were: 1, spinosad spray whenever tick numbers exceeded the threshold; 2, Amitraz spray whenever tick numbers exceeded the threshold; 3, spinosad whenever tick numbers exceeded the threshold for the first 2 months, then Amitraz for 2 months, with alternation every subsequent 2 months. Engorged adult female ticks were collected from each treatment group on 10 or 11 occasions during the study and tested using the larval packet test bioassay (LPT) for acaricide resistance. Spinosad 250 ppm provided effective control of Amitraz-resistant tick populations in the field, using a similar number of treatments as in the Amitraz and rotation groups. The initial infestations of all of the groups resulted in the establishment of populations with in vitro evidence of resistance to Amitraz using the LPT. Treatment with spinosad or with a rotation between spinosad and Amitraz every 2 months resulted in reduced levels of resistance to Amitraz according to the LPT. The animals treated with Amitraz alone showed increasing resistance to Amitraz according to the LPT each summer and autumn with a return to full or almost full susceptibility to Amitraz in early spring in all years. This pattern suggests a relative lack of fitness of Amitraz-resistant ticks that might be exploited by using an acaricide rotation strategy.
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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 Barre, Robert J Miller, Ronald B Davey, Andrew Y Li, Huguette Gaia, Jeanmichel Delathiere, 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, Robert J Miller, Ronald B Davey, Andrew C Chen, 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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Mode of Inheritance of Amitraz Resistance in a Brazilian Strain of the Southern Cattle Tick, Boophilus microplus (Acari: Ixodidae)*
Experimental & Applied Acarology, 2005Co-Authors: Andrew Y Li, Robert J Miller, Ronald B Davey, John E GeorgeAbstract:The southern cattle tick, Boophilus microplus (Canestrini), has developed resistance to Amitraz in several countries in recent years. A study was conducted at the USDA Cattle Fever Tick Research Laboratory in Texas to investigate the mode of inheritance of Amitraz resistance with cross-mating experiments. The Muñoz strain, a laboratory reared acaricide-susceptible reference strain, was used as the susceptible parent and the Santa Luiza strain, originating in Brazil, was used as the resistant parent. A modified Food and Agriculture Organization Larval Packet Test was used to measure the levels of susceptibility of larvae of the parental strains, F_1, backcross, F_2, and F_3 generations. Results of reciprocal crossing experiments suggested that Amitraz resistance was inherited as an incomplete recessive trait. There was a strong maternal effect on larval progeny’s susceptibility to Amitraz in both the F_1 and the subsequent generations. The values of the degree of dominance were estimated at −0.156 and −0.500 for the F_1 larvae with resistant and susceptible female parents, respectively. Results of bioassays on larval progeny of the F_1 backcrossed with the resistant parent strain and that of the F_2 generations suggested that more than one gene was responsible for Amitraz resistance in the Santa Luiza strain. Comparisons of biological parameters (engorged female weight, egg mass weight, and female-to-egg weight conversion efficiency index) indicated significant differences between different genotypes. The differences appeared to be heritable, but not related to Amitraz resistance. Results from this study may have significant implications for the management of Amitraz resistance.
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diagnosis of Amitraz resistance in boophilus microplus in new caledonia with the modified larval packet test
Veterinary Parasitology, 2005Co-Authors: Sophie Ducornez, Robert J Miller, Nicolas Barre, M De GarinewichatitskyAbstract:The tick Boophilus microplus represents a serious pathological constraint to livestock production in New Caledonia. Cattle ticks are controlled by chemical application of two acaricides that are currently used in New Caledonia; deltamethrin is used at 46% of the cattle production facilities and Amitraz at the remaining 54% premises where resistance to deltamethrin has been identified. In 2003, a modified Larval Packet Test (LPT) was used to conduct a survey for Amitraz resistance. Ticks were collected from 29 farms, including farms using deltamethrin (n = 8) or Amitraz (n = 21). Of eighteen different tick populations, sixteen populations were defined susceptible to Amitraz and two populations were considered Amitraz-resistant. This is the first report of populations of B. microplus being resistant to Amitraz, using the modified LPT in New Caledonia. A thorough survey of tick susceptibility to Amitraz in cattle farms of the country should be conducted to assess the presence of Amitraz-resistant populations. The emergence of Amitraz resistance so soon after its introduction has some important implications for the strategy and organisation of tick control in New Caledonia, and this paper discusses some of the urgent actions that should be undertaken.
Andrew Y Li - 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 Barre, Robert J Miller, Ronald B Davey, Andrew Y Li, Huguette Gaia, Jeanmichel Delathiere, 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, Robert J Miller, Ronald B Davey, Andrew C Chen, 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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Mode of Inheritance of Amitraz Resistance in a Brazilian Strain of the Southern Cattle Tick, Boophilus microplus (Acari: Ixodidae)*
Experimental & Applied Acarology, 2005Co-Authors: Andrew Y Li, Robert J Miller, Ronald B Davey, John E GeorgeAbstract:The southern cattle tick, Boophilus microplus (Canestrini), has developed resistance to Amitraz in several countries in recent years. A study was conducted at the USDA Cattle Fever Tick Research Laboratory in Texas to investigate the mode of inheritance of Amitraz resistance with cross-mating experiments. The Muñoz strain, a laboratory reared acaricide-susceptible reference strain, was used as the susceptible parent and the Santa Luiza strain, originating in Brazil, was used as the resistant parent. A modified Food and Agriculture Organization Larval Packet Test was used to measure the levels of susceptibility of larvae of the parental strains, F_1, backcross, F_2, and F_3 generations. Results of reciprocal crossing experiments suggested that Amitraz resistance was inherited as an incomplete recessive trait. There was a strong maternal effect on larval progeny’s susceptibility to Amitraz in both the F_1 and the subsequent generations. The values of the degree of dominance were estimated at −0.156 and −0.500 for the F_1 larvae with resistant and susceptible female parents, respectively. Results of bioassays on larval progeny of the F_1 backcrossed with the resistant parent strain and that of the F_2 generations suggested that more than one gene was responsible for Amitraz resistance in the Santa Luiza strain. Comparisons of biological parameters (engorged female weight, egg mass weight, and female-to-egg weight conversion efficiency index) indicated significant differences between different genotypes. The differences appeared to be heritable, but not related to Amitraz resistance. Results from this study may have significant implications for the management of Amitraz resistance.
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mode of inheritance of Amitraz resistance in a brazilian strain of the southern cattle tick boophilus microplus acari ixodidae
Experimental and Applied Acarology, 2005Co-Authors: Andrew Y Li, Robert J Miller, Ronald B Davey, John E GeorgeAbstract:The southern cattle tick, Boophilus microplus (Canestrini), has developed resistance to Amitraz in several countries in recent years. A study was conducted at the USDA Cattle Fever Tick Research Laboratory in Texas to investigate the mode of inheritance of Amitraz resistance with cross-mating experiments. The Munoz strain, a laboratory reared acaricide-susceptible reference strain, was used as the susceptible parent and the Santa Luiza strain, originating in Brazil, was used as the resistant parent. A modified Food and Agriculture Organization Larval Packet Test was used to measure the levels of susceptibility of larvae of the parental strains, F1, backcross, F2, and F3 generations. Results of reciprocal crossing experiments suggested that Amitraz resistance was inherited as an incomplete recessive trait. There was a strong maternal effect on larval progeny’s susceptibility to Amitraz in both the F1 and the subsequent generations. The values of the degree of dominance were estimated at −0.156 and −0.500 for the F1 larvae with resistant and susceptible female parents, respectively. Results of bioassays on larval progeny of the F1 backcrossed with the resistant parent strain and that of the F2 generations suggested that more than one gene was responsible for Amitraz resistance in the Santa Luiza strain. Comparisons of biological parameters (engorged female weight, egg mass weight, and female-to-egg weight conversion efficiency index) indicated significant differences between different genotypes. The differences appeared to be heritable, but not related to Amitraz resistance. Results from this study may have significant implications for the management of Amitraz resistance.
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detection and characterization of Amitraz resistance in the southern cattle tick boophilus microplus acari ixodidae
Journal of Medical Entomology, 2004Co-Authors: Robert J Miller, Ronald B Davey, Andrew Y Li, John E GeorgeAbstract:Amitraz, a formamidine acaricide, plays an important role in the control of the southern cattle tick, Boophilus microplus (Canestrini), and other tick species that infest cattle, dogs, and wild animals. Although resistance to Amitraz in B. microplus was previously reported in several countries, the actual measurement of the level of Amitraz resistance in ticks has been difficult to determine due to the lack of a proper bioassay technique. We conducted a survey, by using a newly reported technique that was a modification of the standard Food and Agriculture Organization larval packet test, to measure the levels of resistance to Amitraz in 15 strains of B. microplus from four major cattle-producing states in Mexico. Low-order resistance (1.68- to 4.58-fold) was detected in 11 of those strains. Our laboratory selection using Amitraz on larvae of the Santa Luiza strain, which originated from Brazil, achieved a resistance ratio of 153.93 at F6, indicating the potential for high resistance to this acaricide in B. microplus. Both triphenylphosphate and piperonyl butoxide significantly synergized Amitraz toxicity in both resistant and susceptible tick strains. Diethyl maleate synergized Amitraz toxicity in one resistant strain but had no effect on the susceptible strain and had minor antagonistic effects on two other resistant strains. Target site insensitivity, instead of metabolic detoxification mechanisms, might be responsible for Amitraz resistance observed in the Santa Luiza strain and possibly in other Amitraz resistant B. microplus ticks from Mexico. The Santa Luiza strain also demonstrated high resistance to pyrethroids and moderate resistance to organophosphates. Multiple resistance shown in this strain and other B. microplus strains from Mexico poses a significant challenge to the management of B. microplus resistance to acaricides in Mexico.
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 Barre, Robert J Miller, Ronald B Davey, Andrew Y Li, Huguette Gaia, Jeanmichel Delathiere, 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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mutations in a putative octopamine receptor gene in Amitraz resistant cattle ticks
Veterinary Parasitology, 2007Co-Authors: Andrew C Chen, Haiqi He, Ronald B DaveyAbstract:The mode of action of Amitraz is thought to be its toxic effects on a receptor for a neuromodulator, octopamine. Resistance could arise from modifications of this receptor so that it would not be affected by Amitraz. A putative octopamine receptor cDNA was cloned and sequenced from a cattle tick in Australia. However, when the sequence was compared between Australian strains of Amitraz-susceptible and resistant ticks, no differences were detected. We have sequenced this putative octopamine receptor gene in tick strains from America. The American ticks have a sequence almost identical to that of the Australian ticks with no deletions or additions in the open reading frame. In a Brazilian strain and a Mexican strain that are very resistant to Amitraz, there are two nucleotide substitutions that result in amino acids different from all the susceptible strains. Discovery of these mutations only in Amitraz-resistant ticks provides the first evidence for the possibility of an altered pesticide target site as a mechanism of Amitraz resistance in ticks.
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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, Robert J Miller, Ronald B Davey, Andrew C Chen, 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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Mode of Inheritance of Amitraz Resistance in a Brazilian Strain of the Southern Cattle Tick, Boophilus microplus (Acari: Ixodidae)*
Experimental & Applied Acarology, 2005Co-Authors: Andrew Y Li, Robert J Miller, Ronald B Davey, John E GeorgeAbstract:The southern cattle tick, Boophilus microplus (Canestrini), has developed resistance to Amitraz in several countries in recent years. A study was conducted at the USDA Cattle Fever Tick Research Laboratory in Texas to investigate the mode of inheritance of Amitraz resistance with cross-mating experiments. The Muñoz strain, a laboratory reared acaricide-susceptible reference strain, was used as the susceptible parent and the Santa Luiza strain, originating in Brazil, was used as the resistant parent. A modified Food and Agriculture Organization Larval Packet Test was used to measure the levels of susceptibility of larvae of the parental strains, F_1, backcross, F_2, and F_3 generations. Results of reciprocal crossing experiments suggested that Amitraz resistance was inherited as an incomplete recessive trait. There was a strong maternal effect on larval progeny’s susceptibility to Amitraz in both the F_1 and the subsequent generations. The values of the degree of dominance were estimated at −0.156 and −0.500 for the F_1 larvae with resistant and susceptible female parents, respectively. Results of bioassays on larval progeny of the F_1 backcrossed with the resistant parent strain and that of the F_2 generations suggested that more than one gene was responsible for Amitraz resistance in the Santa Luiza strain. Comparisons of biological parameters (engorged female weight, egg mass weight, and female-to-egg weight conversion efficiency index) indicated significant differences between different genotypes. The differences appeared to be heritable, but not related to Amitraz resistance. Results from this study may have significant implications for the management of Amitraz resistance.
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mode of inheritance of Amitraz resistance in a brazilian strain of the southern cattle tick boophilus microplus acari ixodidae
Experimental and Applied Acarology, 2005Co-Authors: Andrew Y Li, Robert J Miller, Ronald B Davey, John E GeorgeAbstract:The southern cattle tick, Boophilus microplus (Canestrini), has developed resistance to Amitraz in several countries in recent years. A study was conducted at the USDA Cattle Fever Tick Research Laboratory in Texas to investigate the mode of inheritance of Amitraz resistance with cross-mating experiments. The Munoz strain, a laboratory reared acaricide-susceptible reference strain, was used as the susceptible parent and the Santa Luiza strain, originating in Brazil, was used as the resistant parent. A modified Food and Agriculture Organization Larval Packet Test was used to measure the levels of susceptibility of larvae of the parental strains, F1, backcross, F2, and F3 generations. Results of reciprocal crossing experiments suggested that Amitraz resistance was inherited as an incomplete recessive trait. There was a strong maternal effect on larval progeny’s susceptibility to Amitraz in both the F1 and the subsequent generations. The values of the degree of dominance were estimated at −0.156 and −0.500 for the F1 larvae with resistant and susceptible female parents, respectively. Results of bioassays on larval progeny of the F1 backcrossed with the resistant parent strain and that of the F2 generations suggested that more than one gene was responsible for Amitraz resistance in the Santa Luiza strain. Comparisons of biological parameters (engorged female weight, egg mass weight, and female-to-egg weight conversion efficiency index) indicated significant differences between different genotypes. The differences appeared to be heritable, but not related to Amitraz resistance. Results from this study may have significant implications for the management of Amitraz resistance.
Rodrigo Rosariocruz - One of the best experts on this subject based on the ideXlab platform.
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development of Amitraz resistance in field populations of boophilus microplus acari ixodidae undergoing typical Amitraz exposure in the mexican tropics
Veterinary Parasitology, 2008Co-Authors: J A Rosadoaguilar, R I Rodriguezvivas, H Fragososanchez, Z Garciavazquez, A Ortiznajera, Rodrigo RosariocruzAbstract:Abstract The purpose of this study was to determine the effect of Amitraz selection pressure on the development of resistance in field populations of Boophilus microplus in the Mexican tropics. Three farms (FA 1 , FA 2 and FA 3 ) in Yucatan, Mexico, were selected in this study. Amitraz was applied as a whole body sprays to all cattle on each farm for tick control once monthly for 15 months. From each farm, 20–30 B. microplus engorged females were collected every 3 months. The modified larval immersion test was used to test susceptibility of B. microplus to Amitraz. Larvae were exposed to serial dilutions of Amitraz. Probit analysis was used to determine lethal dose at 50% mortality and associated 95% confidence limits. The resistance factors found in the three farms during the 15 months of Amitraz selection pressure were FA 1 (1, 2, 4, 4 and 13), FA 2 (1, 6, 23, 21 and 22) and FA 3 (2, 13, 2, 6 and 6). It is concluded that Amitraz selection pressure on field populations of B. microplus increased the resistance level in all populations studied in the Mexican tropics.
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prevalence and potential risk factors for Amitraz resistance in boophilus microplus ticks in cattle farms in the state of yucatan mexico
Preventive Veterinary Medicine, 2006Co-Authors: R I Rodriguezvivas, F Rodriguezarevalo, Miguel Angel Alonsodiaz, H Fragososanchez, V M Santamaria, Rodrigo RosariocruzAbstract:Abstract Southern cattle tick, Boophilus microplus , control in the Mexican tropics is based on the application by spray, dip or pour-on of acaricides. In Mexico the first report of ticks resistant to Amitraz was reported in 2002. Amitraz resistance affecting the cattle industry of Yucatan State, Mexico, has not been investigated. A cross-sectional study was carried out in order to investigate the possible association between management risk factors and the prevalence of B. microplus ticks resistant to Amitraz in Yucatan, Mexico. Ninety-eight cattle farms were randomly selected and a sample of 20–30 engorged B. microplus females was collected from at least 10 cattle from each farm. Collected ticks were taken to the laboratory where the larval progeny were obtained. The modified larval immersion test was used to detect ticks resistant to Amitraz. A discriminating dose of 0.0002% Amitraz was used. A questionnaire was applied on each collaborating farm. For the statistical analysis a 2 × 2 contingency table was used to identify potential risk factors. The prevalence of farms with B. microplus resistant to Amitraz was 19.40%. However, even though tick resistance to Amitraz is a present problem there was no evidence that it was associated with the risk factors analyzed in this survey.
