In vitro efficacy of Duddingtonia flagrans against nematodes of sheep based on in vivo calculations / Eficácia in vitro de Duddingtonia flagrans contra nematoides de ovinos com base em cálculo in vivo

Abstract Duddingtonia flagrans has been tested as an alternative parasite control, but data from in vitro experiments based on in vivo calculations describing nematophagous fungi predation in nematodes are restricted. The objective of this work was to determine the efficacy of D. flagrans against sheep nematode larvae in vitro using in vivo calculations. Fecal samples were introduced to fungi in different concentrations: 0.0/control; 0.05; 0.1; 0.2; 0.4; 0.8; 1.6; 3.2; and 6.4 g corresponding, respectively, to 583.000; 1.166.000; 2.332.000; 4.664.000; 9.328.000; 18.656.000; 37.312.000 and 74.624.000 chlamydospores/kg of body weight. The material was incubated for 14 days, before the larvae recovery (Assay 1). Assay 2 was carried out with the doses of 0.00625; 0.0125; and 0.025 g. The results showed a negative correlation between fungal concentrations and larval numbers for both assays. The fungus demonstrated an efficacy above 89% in both assays. Thus, we consider that the data from in vitro studies based on in vivo calculations may optimize the fungi quantities for field experiments.

Resumo Duddingtonia flagrans tem sido testado como uma alternativa no controle de parasitos, entretanto, trabalhos in vitro da predação de nematoides por fungos nematófagos correlacionados com cálculos baseados para testes in vivo são restritos. O objetivo deste trabalho foi determinar a eficácia in vitro de D. flagrans contra larvas de nematoides de ovinos tendo como base cálculos in vivo. Amostras fecais receberam a adição do fungo em diferentes concentrações: 0.0/controle; 0,05; 0,1; 0,2; 0,4; 0,8; 1,6; 3,2 e 6,4 gramas correspondendo, respectivamente, às seguintes dosagens: 583.000; 1.166.000; 2.332.000; 4.664.000; 9.328.000; 18.656.000; 37.312.000 e 74.624.000 clamidósporos/Kg de peso vivo animal. O material foi incubado por 14 dias, para recuperação das larvas (Ensaio 1). O Ensaio 2 foi realizado com concentrações de 0,00625; 0,0125 e 0,025 g. Foi observada correlação negativa entre a concentração fúngica e o número de larvas, nos dois ensaios. O fungo demonstrou eficácia acima de 89% em ambos os ensaios. A partir destes dados, acreditamos que ensaios in vitro baseados em cálculos in vivo podem aprimorar as dosagens para a realização de experimentos a campo.

The potassium impermeable apical membrane of insect epithelia: a target for development of safe pesticides

Columnar cell apical membranes (CCAM) in series with goblet cell apical membranes (GCAM) form an electroosmotic barrier separating the midgut lumen from epithelial cell cytoplasm. A unique K+ ATPase in GCAM generates three gradients across this barrier. A greater than 180 mV electrical gradient (lumen positive) drives amino acid uptake through voltage-dependent K+ symports. A greater than 1000-fold [H+] gradient (lumen alkaline) and a greater than 10-fold [K+] gradient (lumen concentrated) are adaptations to the high tannin and high K+ content, respectively, in dietary plant material. Agents which act on the apical membrane and disrupt the PD, H+, or K+ gradients are potential insecticides. Insect sensory epithelia and mammalian stria vascularis maintain similar PD and K+ gradients but would not be exposed to ingested anti-apical membrane insecticides. Following the demonstration by Sacchi et al. that Bacillus thuringiensis delta-endotoxin (Bt) induces specifically a K+ conductance increase in CCAM vesicles, we find that the K+ channel blocking agent, Ba2+, completely reverses Bt inhibition of the K+-carried short circuit current in the isolated midgut of Manduca sexta. Progress in characterizing the apical membrane includes finding that fluorosulfonylbenzoyladenosine binds specifically to certain GCAM polypeptides and that CCAM vesicles can be mass produced by Ca2+ or Mg2+ precipitation from Manduca sexta midgut.