Antonio Thadeu Medeiros de Barros

Reassessment of the potential economic impact of cattle parasites in Brazil

The profitability of livestock activities can be diminished significantly by the effects of parasites. Economic losses caused by cattle parasites in Brazil were estimated on an annual basis, considering the total number of animals at risk and the potential detrimental effects of parasitism on cattle productivity. Estimates in U.S. dollars (USD) were based on reported yield losses among untreated animals and reflected some of the effects of parasitic diseases. Relevant parasites that affect cattle productivity in Brazil, and their economic impact in USD billions include: gastrointestinal nematodes -

Horn fly (Diptera: Muscidae) resistance to organophosphate insecticides

7.11; cattle tick (Rhipicephalus (Boophilus) microplus) -

Seasonality and relative abundance of Tabanidae (Diptera) captured on horses in the Pantanal, Brazil

3.24; horn fly (Haematobia irritans) -

Suscetibilidade de Rhipicephalus (Boophilus) microplus a carrapaticidas em Mato Grosso do Sul, Brasil

2.56; cattle grub (Dermatobia hominis) -

Evaluation of a yearly insecticidal ear tag rotation for control of pyrethroid-resistant horn flies (Diptera: Muscidae)

0.38; New World screwworm fly (Cochliomyia hominivorax) -

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

0.34; and stable fly (Stomoxys calcitrans) -

Seroprevalence and risk factors for cattle anaplasmosis, babesiosis, and trypanosomiasis in a Brazilian semiarid region

0.34. The combined annual economic loss due to internal and external parasites of cattle in Brazil considered here was estimated to be at least USD 13.96 billion. These findings are discussed in the context of methodologies and research that are required in order to improve the accuracy of these economic impact assessments. This information needs to be taken into consideration when developing sustainable policies for mitigating the impact of parasitism on the profitability of Brazilian cattle producers.

Insecticide susceptibility of horn flies, Haematobia irritans (Diptera: Muscidae), in the State of Mato Grosso do Sul, Brazil

Insecticidal ear tags impregnated with organophosphate (OP) insecticides were used each year from 1989 to 1998 at Rosepine, LA. Weekly fly counts were conducted to evaluate control efficacy of the treatments, and bioassays were conducted at least twice per year to measure fly susceptibility to OP and pyrethroid insecticides. Between 1989 and 1992, the efficacy of 20% diazinon-impregnated ear tags was reduced from >20 to just 1 week of control. A high risk of control failure was observed when a resistance frequency of approximately 5% was measured in pre-season bioassays. Resistance to diazinon, fenthion, ethion, pirimiphos-methyl, and tetrachlorvinphos was observed. Esterase activity toward alpha-naphthyl acetate was significantly higher in flies collected at Rosepine in 1997 than in flies from a laboratory colony and from a susceptible field population.

Susceptibility to diazinon in populations of the horn fly, Haematobia irritans (Diptera: Muscidae), in Central Brazil.

Once a month, from June 1992 to May 1993, collections of tabanids on horse were conducted in the Nhecolândia, Pantanal State of Mato Grosso do Sul, Brazil. Tabanid catches using hand nets were conducted from sunrise to sunset at grassland and cerradão (dense savanna) habitats. A total of 3,442 tabanids from 21 species,12 genera, and 3 subfamilies were collected. Although species abundance varied seasonally depending on habitat, no habitat specificity was observed for the most abundant species. In the grassland, 1,625 (47.2%) tabanids belonging to 19 species were collected, while 1,817 (52.8%) tabanids from 17 species were caught in the cerradão. The number of tabanid species varied from 7 during winter (July/August) to 15 in the spring (October). Tabanus importunus (56%) was the most abundant species, followed by T. occidentalis (8.2%), and T. claripennis (8.1%). The tabanid peak, in October, coincided with the beginning of the rainy season. The population peak of most species, including those with higher vector potential, suggests that the rainy season can be considered as the period of potentially higher risk of mechanical transmission of pathogens by tabanids to horses in the region.

Surtos por Stomoxys calcitrans em gado de corte no Mato Grosso do Sul

The cattle tick, Rhipicephalus (Boophilus) microplus, is one of the most important ectoparasites of bovines, requiring adoption of control measures mainly in Bos taurus herds and its crossbreeds. Its control has becoming increasingly difficult due to selection of resistant populations by commercial products. This study aimed to know the status of cattle tick resistance to acaricides in the state of Mato Grosso do Sul. From October 2003 to October 2006 acaricide bioassays were conducted on cattle ticks from eleven of the most important livestock regions of the state. Adult immersion tests using regular commercial products according to label recommendations were followed by the evaluation of biological parameters. Twelve acaricide products containing one or more of seven active ingredients, from three chemical classes: amidine (amitraz), synthetic pyrethroid (cypermethrin), and organophosphates (chlorfenvinphos, chlorpyriphos, diazinon, dichlorvos, and ethion) were tested. Low tick susceptibility was observed in all ranches, with several populations showing virtually no susceptibility to one or more products. Despite the great variation of susceptibility shown by the populations to each acaricide, a gradient of efficacy of these products was observed. Regardless of the acaricide class, the average efficacy of products containing a single active ingredient (19.94%-64.27%) was generally lower than that showed by the mixtures, pyrethroid-organophosphate (46.38%-82.68%) and between organophosphates (85.28%-97.68%). The mixture containing pyrethroid + OF + synergist + repellent (cypermethrin + chlorpyrifos + citronellal + piperonyl butoxide) showed 100% efficacy, although it was tested in a smaller number of populations. Although comparisons with a susceptible strain have not been made, the low efficacy showed by the several different products tested, strongly suggests that tick resistance is widespread in the state. For this reason, it is recommended the routine peruse of susceptibility tests before selection and use of acaricide products for tick control.