Pathogenicity of Metarhizium anisopliae towards Rhipicephalus (Boophilus) microplus under laboratory and field conditions

Metarhizium anisopliae is one of the most studied agents of biological control of several arthropod plagues, including the cattle tick Rhipicephalus (Boophilus) microplus. Studies have been conducted to assess the fungal complex infection process towards its hosts. To accomplish that, mutant strains overexpressing or lacking assumed determinant genes for the process were constructed over the years. A fundamental experiment to demonstrate a particular gene or set of genes participation is the bioassay. The comparison of bioassays using wild and engineered strains is an essential tool to affirm a given gene is crucial in the process. Therefore, the in vitro bioassays should mimic the results obtained in tests under field conditions. In this study, tests under laboratory and filed conditions were done and a correlation analysis was performed in order to statistically validate in vitro bioassays. Tick egg laying, larvae hatching and host mortality were recorded in each experiment through 21 days, both under laboratory and field conditions. In all cases, M. anisopliae treatments were statistically different from the control treatments. A linear regression analysis was performed between the cases. Laboratory results showed a statistically significant correlation with the field conditions using the Pearson's Correlation Test (P < 0.01 host mortality - 0.969, tick egg laying - 0.977 and larvae hatching - 0.956). These results legitimize the in vitro bioassays and, therefore, constitute them as a valid tool for studying this fungus behavior, so they can be used to infer M. anisopliae response towards R. (Boophilus) microplus.

Acaricidal action of destruxins produced by a marine-derived Beauveria felina on the bovine tick Rhipicephalus (Boophilus) microplus

The increasing resistance of Rhipicephalus (Boophilus) microplus tick to commercial insecticides requires alternative methods for the control of this cattle plague. The enthomopathogenic fungus Beauveria feline produces destruxins in culture media, cyclic depsipeptides which display an array of biological activities. The present investigation aimed to evaluate the acaricide action of destruxins isolated from B. felina culture media on R. (B.) microplus engorged females. B. felina was grown in MF medium under 19 different growth conditions. HPLC-PDA analysis of chromatographic fractions obtained from the 19 different growth media extracts indicated the presence of destruxins in all lipophylic fractions. Such fractions were combined and subjected to separation by HPLC. Fractions containing distinct destruxins composition were tested against R. (B.) micro plus. Two fractions, composed of destruxin Ed(1) and pseudodestruxin B and/or pseudodestruxin C (fraction P1) as well as by hydroxyhomodestruxin B and/or destruxin D and/or roseotoxin C (fraction P7), displayed 30% and 28.7% acaricidal efficacy, respectively. This activity profile in such low concentration is adequate to consider destruxins as potential leading compounds to be developed for tick biological control. (C) 2012 Elsevier Inc. All rights reserved.

Sequencing a new target genome: The Boophilus microplus (Acari : Ixodidae) genome project

The southern cattle tick, Boophilus microplus (Canestrini), causes annual economic losses in the hundreds of millions of dollars to cattle producers throughout the world, and ranks as the most economically important tick from a global perspective. Control failures attributable to the development of pesticide resistance have become commonplace, and novel control technologies are needed. The availability of the genome sequence will facilitate the development of these new technologies, and we are proposing sequencing to a 4-6X draft coverage. Many existing biological resources are available to facilitate a genome sequencing project, including several inbred laboratory tick strains, a database of approximate to 45,000 expressed sequence tags compiled into a B. microplus Gene Index, a bacterial artificial chromosome (BAC) library, an established B. microplus cell line, and genomic DNA suitable for library synthesis. Collaborative projects are underway to map BACs and cDNAs to specific chromosomes and to sequence selected BAC clones. When completed, the genome sequences from the cow, B. microphis, and the B. microphis-borne pathogens Babesia bovis and Anaplasma marginale will enhance studies of host-vector-pathogen systems. Genes involved in the regeneration of amputated tick limbs and transitions through developmental stages are largely unknown. Studies of these and other interesting biological questions will be advanced by tick genome sequence data. Comparative genomics offers the prospect of new insight into many, perhaps all, aspects of the biology of ticks and the pathogens they transmit to farm animals and people. The B. microplus genome sequence will fill a major gap in comparative genomics: a sequence from the Metastriata lineage of ticks. The purpose of the article is to synergize interest in and provide rationales for sequencing the genome of B. microplus and for publicizing currently available genomic resources for this tick.

The productivity effects of cattle tick (Boophilus microplus) infestation on cattle, with particular reference to Bos indicus cattle and their crosses

In response to uncertainty among cattle producers in Australia regarding the need to treat Bos indices and B. indicus crossbreeds, the scientific literature relating to the productivity effects of Boophilus microplus on cattle of all breeds was reviewed. Estimates of the mean effect of each engorging tick (damage coefficient, d) were made from a simple analysis of the reported data. On average, each engorging female tick is responsible for the loss of 1.37 +/- 0.25 g bodyweight in B. taunts cattle. The comparable value for B. taurus x B. indicus cattle is 1.18 +/- 0.21 g/engorging tick. These values were not statistically significantly different, indicating that if a threshold approach to tick control were taken, then the threshold number of standard ticks would be the same regardless of cattle genotype. No studies provided useable estimates of the effect of tick infestation on pure B. indices cattle. An economic threshold for treatment, below which acaricide application is not beneficial, can be predicted, using known values for the cost of acaricide application and the price of beef. However, the application of a threshold approach to control has not been embraced by government advisers and runs contrary to the accepted principals of strategic control programs. (C) 2006 Elsevier B.V. All rights reserved.

Efeito acaricida in vitro de extratos vegetais de plantas do Bioma Pampa sobre larvas de Rhipicephalus (Boophilus) microplus (Acari: Ixodidae).

Os antiparasitários ainda são a principal forma de controle do carrapato em todo o mundo. Entretanto, seu uso como única forma de controle e a falta de assistência técnica a produtores sobre sua aplicação correta tem levado desenvolvimento da resistência dos parasitas e aumento do risco de ocorrência de resíduos químicos na carne e no leite.

Efeito acaricida in vivo do extrato aquoso de Daphnopsis racemosa e de Natur N sobre larvas e ninfas de Rhipicephalus (Boophilus) microplus.

As limitações atuais do controle químico parasitário e a riqueza e grande diversidade da flora brasileira têm estimulado a pesquisa com extratos de plantas na busca por novas formas de controle.

Estudo do nível de infecção por Babesia bovis e Babesia bigemina em bovinos da raça canchim naturalmente infestados com o carrapato Rhipicephalus (Boophilus) microplus.

Entre as principais causas de perdas produtivas em bovinos criados nos trópicos está a infestação pelo carrapato Rhipicephalus (Boophilus) microplus e, consequentemente, dos hemoparasitas transmitidos por ele. A resistência dos zebuínos e de animais cruzados com raças taurinas à infestação por esse ácaro é amplamente conhecida. Entretanto, no que se refere à suscetibilidade às babesioses bovinas, existem evidências de que o grupo genético também pode interferir na resistência, seguindo o mesmo padrão observado para o carrapato vetor, com os taurinos apresentando maior sensibilidade. Assim, este estudo teve por objetivo avaliar a parasitemia por Babesia bovis e Babesia bigemina em 50 novilhas da raça Canchim ( Charolês + Zebu) naturalmente infestadas pelo R. (B.) microplus nas quatro estações do ano durante 24 meses, além de caracterizar o perfil de citocinas que podem estar associados ao fenótipo de resistência e suscetibilidade aos hemoparasitas do gênero Babesia spp. Foram realizadas contagens de fêmeas adultas de carrapatos com tamanho igual ou superior a 4,5 mm de diâmetro, presentes no lado esquerdo de cada bovino. As amostras de DNA extraídas foram submetidas à amplificação por meio da Reação em Cadeia da Polimerase Quantitativa em Tempo Real (qPCR), utilizando iniciadores que flanqueiam fragmentos dos genes mitocondriais do citocromo b (mt-cyt B), específicos para B. bovis e B. bigemina. O RNA extraído do sangue, foi usado para sintetizar o DNA complementar (cDNA) para análise de expressão dos genes do IFN- , TNF- , IL-10 e IL-12B por meio da quantificação relativa (RTqPCR). Foram observadas diferenças significativas (P<0,05) entre os meses das avaliações para a contagem de carrapatos. Entretanto, não houve efeito significativo (P>0,05) nas colheitas realizadas entre novembro de 2013 a janeiro de 2014 e entre os meses janeiro e fevereiro de 2015. A frequência da parasitemia no rebanho foi de 98%. Dentre as amostras de DNA que puderam ser quantificadas pela qPCR, 98% e 95,4% foram positivas para B. bovis e B. bigemina, respectivamente. Com relação ao número de cópias (NC) dos fragmentos dos genes mt-cyt B específicos para B. bovis e B. bigemina foram observados efeitos significativos (P<0,05) para ambas as espécies e interação das mesmas com as colheitas realizadas nas diferentes estações do ano. A análise do nível de expressão de mRNA do IFN- , TNF- e IL-12B revelou que houve um efeito siginificativo (P<0,05) da interação entre animais dos extremos de resistência/suscetibilidade e estações do ano, exceto para IL-10. Conclui-se que, a qPCR apresenta alta sensibilidade e especificidade para o diagnóstico das babesioses bovinas em amostras de sangue e que a oscilação na carga parasitária nas diferentes estações do ano pode estar associada com o perfil de expressão de citocinas apresentada.