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Amitraz

The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform

John E George – 1st expert on this subject based on the ideXlab platform

  • 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, 2008
    Co-Authors: Nicolas Barre, Robert J Miller, Ronald B Davey, Andrew Y Li, Huguette Gaia, Jeanmichel Delathiere, John E George

    Abstract:

    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.

  • acaricide resistance and synergism between permethrin and Amitraz against susceptible and resistant strains of boophilus microplus acari ixodidae
    Pest Management Science, 2007
    Co-Authors: Andrew Y Li, Robert J Miller, Ronald B Davey, Andrew C Chen, John E George

    Abstract:

    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

  • Mode of Inheritance of Amitraz Resistance in a Brazilian Strain of the Southern Cattle Tick, Boophilus microplus (Acari: Ixodidae)*
    Experimental & Applied Acarology, 2005
    Co-Authors: Andrew Y Li, Robert J Miller, Ronald B Davey, John E George

    Abstract:

    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.

Robert J Miller – 2nd expert on this subject based on the ideXlab platform

  • rotation of treatments between spinosad and Amitraz for the control of rhipicephalus boophilus microplus populations with Amitraz resistance
    Veterinary Parasitology, 2010
    Co-Authors: N N Jonsson, Robert J Miller, D H Kemp, A Knowles, A E Ardila, R G Verrall, J T Rothwell

    Abstract:

    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.

  • 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, 2008
    Co-Authors: Nicolas Barre, Robert J Miller, Ronald B Davey, Andrew Y Li, Huguette Gaia, Jeanmichel Delathiere, John E George

    Abstract:

    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.

  • acaricide resistance and synergism between permethrin and Amitraz against susceptible and resistant strains of boophilus microplus acari ixodidae
    Pest Management Science, 2007
    Co-Authors: Andrew Y Li, Robert J Miller, Ronald B Davey, Andrew C Chen, John E George

    Abstract:

    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

Andrew Y Li – 3rd expert on this subject based on the ideXlab platform

  • 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, 2008
    Co-Authors: Nicolas Barre, Robert J Miller, Ronald B Davey, Andrew Y Li, Huguette Gaia, Jeanmichel Delathiere, John E George

    Abstract:

    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.

  • acaricide resistance and synergism between permethrin and Amitraz against susceptible and resistant strains of boophilus microplus acari ixodidae
    Pest Management Science, 2007
    Co-Authors: Andrew Y Li, Robert J Miller, Ronald B Davey, Andrew C Chen, John E George

    Abstract:

    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

  • Mode of Inheritance of Amitraz Resistance in a Brazilian Strain of the Southern Cattle Tick, Boophilus microplus (Acari: Ixodidae)*
    Experimental & Applied Acarology, 2005
    Co-Authors: Andrew Y Li, Robert J Miller, Ronald B Davey, John E George

    Abstract:

    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.