A comparison of three different methodologies for evaluating Rhipicephalus (Boophilus) microplus susceptibility to topical spray compounds.

This study aimed to compare three different methodologies (Adult Immersion Tests, field trials with naturally infected animals, and a Stall Test using artificially infested cattle) to evaluate the efficacy of two topical formulations that we administered as whole body sprays (15% Cypermethrin+30% Chlorpyriphos+15% Fenthion-Colosso(®) FC 30, Ouro Fino Agronegócios; and 60% Dichlorvos+20% Chlorpyriphos-Ectofós(®), Vallée Saúde Animal Ltd.), against a susceptible strain of Rhipicephalus (Boophilus) microplus. To achieve this objective, two natural infestation trials were conducted, as well as two artificial infestation trials (Stall Tests) and two Adult Immersion Tests (AIT). The AIT results showed that both spray formulations achieved 100% efficacy against R. (B.) microplus fully engorged females. However, when observing results obtained by field trials (natural infestations) and Stall Tests, none of these topically applied compounds reached 100% efficacy or affected the reproductive capacity of the fully engorged female ticks. Additional studies must be conducted to compare these in vivo methodologies with different in vitro techniques, such as the Larval Packet Test. However, based on results obtained here, we can conclude that depending on the spray formulations used, the AIT can overestimate acaricidal efficacy and values of reproductive efficiency of such compounds against R (B.) microplus. Specifically, when dealing with spray formulations in the Stall Tests, the period of residual action can increase because these animals are sheltered from contact with environmental factors that might interfere with the efficacy of the products tested. It may be necessary to take in vivo trial results into consideration (such as field trials with naturally infested animals or Stall Tests) to standardize a specific in vitro assay, such as the Adult Immersion Test.

Toxicidade aguda do praguicida organofosforado diclorvos e da mistura com o piretróide deltametrina em Danio rerio e Hyphessobrycon bifasciatus / Acute toxicity of the organophosphorus pesticide diclorvos and the mix with the piretroid deltamethrin in Danio rerio and Hyphessobrycon bifasciatus

Praguicidas como o Diclorvos (DDVP) e a Deltametrina (DTM) são comumente usados na produção agrícola. Para avaliar a toxicidade de formulações comerciais do DDVP e da mistura deste com a DDM, foram realizados testes de toxicidade aguda em peixes da espécie Danio rerio e Hyphessobrycon bifasciatus. Para a mistura, foram utilizadas as maiores concentrações dos praguicidas testados, que não provocaram letalidade. Os resultados obtidos mostraram que, nas concentrações empregadas, o praguicida DDVP promove o efeito “tudo ou nada”. No caso da mistura, verificou-se a ocorrência de 100% de letalidade em concentrações dos praguicidas que não produziram letalidade se administradas isoladamente. Desta forma, evidenciou-se efeito sinérgico dos praguicidas, sugerindo que o emprego de misturas destes praguicidas pode representar um fator importante. Finalmente, o efeito da toxicidade apresentada pelas duas espécies foi similar, sugerindo que Hyphessobrycon bifasciatus pode ser útil no caso de avaliações ambientais nas condições nacionais.

Pesticides such as Dichlovos (DDVP) and Deltamethrin (DTM) are commonly used in agricultural production. To evaluate the toxicity of commercial formulations of DDVP, mixed or not with DTM, were realized tests for acute toxicity in fish species Danio rerio and Hyphessobrycon bifasciatus. To the mixture, we used the highest concentrations of pesticides tested, which caused no lethality. The results showed that on the concentrations used, the pesticide DDVP promotes the "all or nothing effect, i.e. 100% of animals dying or 100% survive. In the case of the mixture, the results demonstrated the occurrence of 100% lethality at concentrations of pesticides that did not produce lethal effect if administered alone, indicating a synergistic effect of the pesticide mixture. These data suggest that the use of mixtures of these pesticides may represent an important factor. Finally, the toxicity effect showed on the two species was similar, suggesting that the Hyphessobrycon bifasciatus fish may be used for environmental assessments in Brazilian conditions.

Toxicidade aguda do praguicida organofosforado diclorvos e da mistura com o piretróide deltametrina em Danio rerio e Hyphessobrycon bifasciatus / Acute toxicity of the organophosphorus pesticide diclorvos and the mix with the piretroid deltamethrin in Danio rerio and Hyphessobrycon bifasciatus

Praguicidas como o Diclorvos (DDVP) e a Deltametrina (DTM) são comumente usados na produção agrícola. Para avaliar a toxicidade de formulações comerciais do DDVP e da mistura deste com a DDM, foram realizados testes de toxicidade aguda em peixes da espécie Danio rerio e Hyphessobrycon bifasciatus. Para a mistura, foram utilizadas as maiores concentrações dos praguicidas testados, que não provocaram letalidade. Os resultados obtidos mostraram que, nas concentrações empregadas, o praguicida DDVP promove o efeito “tudo ou nada”. No caso da mistura, verificou-se a ocorrência de 100% de letalidade em concentrações dos praguicidas que não produziram letalidade se administradas isoladamente. Desta forma, evidenciou-se efeito sinérgico dos praguicidas, sugerindo que o emprego de misturas destes praguicidas pode representar um fator importante. Finalmente, o efeito da toxicidade apresentada pelas duas espécies foi similar, sugerindo que Hyphessobrycon bifasciatus pode ser útil no caso de avaliações ambientais nas condições nacionais.(AU)

Pesticides such as Dichlovos (DDVP) and Deltamethrin (DTM) are commonly used in agricultural production. To evaluate the toxicity of commercial formulations of DDVP, mixed or not with DTM, were realized tests for acute toxicity in fish species Danio rerio and Hyphessobrycon bifasciatus. To the mixture, we used the highest concentrations of pesticides tested, which caused no lethality. The results showed that on the concentrations used, the pesticide DDVP promotes the "all or nothing effect, i.e. 100% of animals dying or 100% survive. In the case of the mixture, the results demonstrated the occurrence of 100% lethality at concentrations of pesticides that did not produce lethal effect if administered alone, indicating a synergistic effect of the pesticide mixture. These data suggest that the use of mixtures of these pesticides may represent an important factor. Finally, the toxicity effect showed on the two species was similar, suggesting that the Hyphessobrycon bifasciatus fish may be used for environmental assessments in Brazilian conditions.(AU)

Effect of short-term exposure to dichlorvos on synaptic plasticity of rat hippocampal slices: involvement of acylpeptide hydrolase and alpha(7) nicotinic receptors.

Dichlorvos is the active molecule of the pro-drug metrifonate used to revert the cognitive deficits associated with Alzheimer's disease. A few years ago it was reported that dichlorvos inhibits the enzyme acylpeptide hydrolase at lower doses than those necessary to inhibit acetylcholinesterase to the same extent. Therefore, the aim of our investigation was to test the hypothesis that dichlorvos can enhance synaptic efficacy through a mechanism that involves acylpeptide hydrolase instead of acetylcholinesterase inhibition. We used long-term potentiation induced in rat hippocampal slices as a model of synaptic plasticity. Our results indicate that short-term exposures (20 min) to 50 microM dichlorvos enhance long-term potentiation in about 200% compared to the control condition. This effect is correlated with approximately 60% inhibition of acylpeptide hydrolase activity, whereas acetylcholinesterase activity remains unaffected. Paired-pulse facilitation and inhibition experiments indicate that dichlorvos does not have any presynaptic effect in the CA3-->CA1 pathway nor affect gabaergic interneurons. Interestingly, the application of 100 nM methyllicaconitine, an alpha(7) nicotinic receptor antagonist, blocked the enhancing effect of dichlorvos on long-term potentiation. These results indicate that under the exposure conditions described above, dichlorvos enhances long-term potentiation through a postsynaptic mechanism that involves (a) the inhibition of the enzyme acylpeptide hydrolase and (b) the modulation of alpha(7) nicotinic receptors.