Atividade larvicida de Anacardium occidentale como alternativa ao controle de Aedes aegypti e sua toxicidade em Rattus norvegicus / Larvicidal activity of Anacardium occidentale as an alternative to control Aedes aegypti and its toxicity in Rattus norvegicus

A busca por substitutos para os inseticidas sintéticos tem estimulado muitos trabalhos científicos contemplando inclusive a utilização de óleos, extratos, ou constituintes ativos provenientes de plantas. Esta procura pode ser justificada pelo potencial inseticida associado à fácil degradação de seus constituintes, menor toxicidade ao homem e uma alternativa mais segura para o meio ambiente. Após a coleta e aquecimento dos frutos de Anacardium occidentale (Anacardiaceae) a 40°C, obteve-se um líquido da castanha de caju (LCC) que, depois de testado quanto à sua atividade larvicida, foi fracionado em coluna de sílica gel dando origem a oito frações, as quais foram codificadas como AO1 a AO8 e submetidas a ensaios larvicidas. Avaliou-se também sua toxicidade oral aguda em Rattus norvegicus. O LCC e as frações AO2 e AO3 apresentaram atividade larvicida para Aedes aegypti. As concentrações letais, CL50 e CL90 do LCC foram, respectivamente, de 6,55 e 10,98 ppm. Para AO2 e AO3, as CL50 e CL90 foram de 3,18 e 7,80 ppm, e de 3,57 e 10,47 ppm, respectivamente. Não foi observada nenhuma toxicidade do LCC e das frações para R. norvegicus. O LCC e as frações foram administrados por via oral na dose de 2000 mg/kg. Esses produtos apresentaram potencial larvicida sobre Ae. aegypti e nenhum sinal de toxicidade foi evidenciado nos parâmetros analisados.

The search for substitutes for synthetic pesticides has been the subject of many scientific publications, including considering the use of oils, extracts and active constituents from plants. This demand can be justified by the insecticide potential associated with an easy degradation of its constituents, lower toxicity to humans and, consequently, a safer alternative for the environment. After collecting and heating the Anacardium occidentale (Anacardiaceae) fruits at 40°C, they were tested to confirm their larvicidal activity. Then, it was fractionated in a silica gel column. The fractionation resulted in eight fractions, which were coded as AO1 to AO8. In this paper, the cashew nut shell liquid (CNSL) and its fractions were evaluated as to their biological activity in the third instar larvae of Aedes aegypti. The acute oral toxicity in Rattus norvegicus also was evaluated. CNSL and the AO2 and AO3 fractions presented larvicidal activity. The lethal concentrations, LC50 and LC90, of CNSL were, respectively, 6.55 and 10.98 ppm. The active fractions, AO2 and AO3, presented LC50 and LC90 of 3.18 and of 7.80 ppm, and 3.57 and 10.47 ppm, respectively. The LCC and the fractions were orally administered at a dose of 2000 mg/kg. These products showed larvicidal potential against Ae. aegypti and no sign of toxicity was evident in the parameters analyzed.

Impact of moisture on survival of Aedes aegypti eggs and ovicidal activity of Metarhizium anisopliae under laboratory conditions

The effect of relative humidity (43 percent, 75 percent, 86 percent and > 98 percent) on Aedes aegypti eggs treated with Metarhizium anisopliae or water only was tested for up to a six months exposure at 25ºC. Survival of larvae inside eggs was clearly affected by the lowest humidity (43 percent) tested, and eclosion diminished at all humidities after increasing periods of exposure. M. anisopliae showed to have a strong ovicidal activity only at humidity close to saturation. No difference of activity was found between conidia and hyphal bodies tested. This fungus affected larvae inside eggs and has potential as a control agent of this important vector in breeding sites with high moisture.